A comparison of commonly used QT correction formulae: the effect of heart rate on the QTc of normal ECGs

Children and Adolescent Patients with Variants in the ATP1A3 -encoded Sodium-Potassium ATPase Alpha-3 Subunit Demonstrate an Impaired QT Response to Bradycardia and Predisposition to Sinus Node Dysfunction

Background

Alternating hemiplegia of childhood (AHC) is a rare disorder with both neurologic and cardiac manifestations. The ATP1A3-D801N variant is associated with a pathologically short QT interval and risk of ventricular arrhythmia following bradycardia; however, the mechanism of this remains unknown. We investigated the relationship between heart rate (HR), QT, and QTc, hypothesizing that individuals with ATP1A3-D801N have abnormal, impaired shortening of QT and QTc at lower HR leading to arrhythmia predisposition.

Methods

We performed a retrospective observational study of individuals who underwent clinical evaluation, Holter monitoring, and genetic testing for AHC at Duke University Hospitals. We also compiled a group of healthy individuals as a control cohort. A larger, worldwide cohort of individuals with ATP1A3 -related phenotypes was compiled to investigate sinus node dysfunction. Linear regression analysis was then performed.

Results

The cohort consisted of 44 individuals with ATP1A3 -related phenotypes with 81 Holter recordings (52.27% female; mean age at first Holter 8.04 years, range 0.58 - 33 years), compared to 36 healthy individuals with 57 Holter recordings (52.78% female; mean age at first Holter 9.84 years, range 0.08 - 38 years). Individuals with ATP1A3-D801N had reduced prolongation of QT at lower HR, manifest as a significantly lower slope for HR vs QT compared to healthy (P<0.0001). This resulted in a significantly higher slope of the relationship for HR vs QTc compared to healthy (P<0.0001). Individuals with ATP1A3 -related phenotypes and baseline QTc <350 milliseconds (ms) had increased shortening of QT and QTc at lower HR compared to those with normal QTc (P=0.003; P=0.001). Among worldwide cases, 3 out of 131 individuals with ATP1A3 -related phenotypes required device implantation and/or had sinus pauses >4 seconds.

Conclusions

Individuals with the ATP1A3-D801N variant exhibit paradoxical shortening of QT and QTc at lower HR, which contributes to an increased risk of arrhythmias during bradycardia. This is exacerbated by an underlying risk of sinus node dysfunction.

Clinical Perspective

What is Known:Individuals with ATP1A3-D801N have a short baseline QTc.Two individuals with AHC experienced ventricular fibrillation following bradycardia.What the Study Adds:The QT and QTc shorten to a greater extent at lower heart rate in individuals with ATP1A3-D801N than in healthy individuals. Individuals with ATP1A3 -related phenotypes and QTc <350ms show greater impairment of QT and QTc dynamics than those with normal QTc. There is low prevalence of device implantation and significant sinus pauses in individuals with ATP1A3 -related phenotypes, with a relatively greater prevalence in those with ATP1A3-D801N.

Amiodarone Therapy: Updated Practical Insights

Amiodarone, a bi-iodinated benzofuran derivative, is among the most commonly used antiarrhythmic drugs due to its high level of effectiveness. Though initially categorized as a class III agent, amiodarone exhibits antiarrhythmic properties across all four classes of antiarrhythmic drugs. Amiodarone is highly effective in maintaining sinus rhythm in patients with paroxysmal atrial fibrillation while also playing a crucial role in preventing a range of ventricular arrhythmias. Amiodarone has a complex pharmacokinetic profile, characterized by a large volume of distribution and a long half-life, which can range from several weeks to months, resulting in prolonged effects even after discontinuation. Side effects may include thyroid dysfunction, pulmonary fibrosis, and hepatic injury, necessitating regular follow-ups. Additionally, amiodarone interacts with several drugs, including anticoagulants, which must be managed to prevent adverse effects. Therefore, a deep understanding of both oral and intravenous formulations, as well as proper dosage adjustments, is essential. The aim of this paper is to provide a comprehensive and updated review on amiodarone's indications, contraindications, recommended dosages, drug interactions, side effects, and monitoring protocols.

Prevalence, Outcomes, and Predictors of Prolonged Corrected QT Interval in Hydroxychloroquine-Naïve Hospitalized COVID-19 Patients

The studies regarding prevalence, outcomes, and predictors of prolonged corrected QT (QTc) among COVID-19 patients not on QTc-prolonging medication are not available in the literature. In this retrospective cohort study, the QTc of 295 hospital-admitted COVID-19 patients was analyzed and its association with in-hospital mortality was determined. The QTc was prolonged in 14.6% (43/295) of the study population. Prolonged QTc was seen in patients with older age (P = 0.018), coronary artery disease (P = 0.001), congestive heart failure (P = 0.042), elevated N-terminal-pro-B-type natriuretic peptide (NT-ProBNP) (P < 0.0001), and on remdesivir (P = 0.046). No episode of torsades de pointes arrhythmia or any arrhythmic death was observed among patients with prolonged QTc. The mortality was significantly high in patients with prolonged QTc (P = 0.003). The multivariate logistic regression analysis showed coronary artery disease (odds ratio (OR): 4.153, 95% CI 1.37-14.86; P = 0.013), and NT-ProBNP (ng/L) (OR: 1.000, 95% CI 1.000-1.000; P = 0.007) as predictors of prolonged QTc. The prolonged QTc was associated with the worst in-hospital survival (p by log-rank 0.001). A significant independent association was observed between prolonged QTc and in-hospital mortality in multivariate cox-regression analysis (adjusted hazard ratio: 3.861; (95% CI 1.719-6.523), P < 0.0001). QTc was found to be a marker of underlying comorbidities among COVID-19 patients. Prolonged QTc in hospitalized COVID-19 patients was independently associated with in-hospital mortality.

Validation of a Demography-Based Adaptive QTc Formula using Pediatric and Adult Datasets Acquired from Humans and Guinea Pigs

Introduction

A variety of QT rate-correction (QTc) formulae have been utilized for both clinical and research purposes. However, these formulae are not universally effective, likely due to significant influences of demographic diversity on the QT-HR relationship. To address this limitation, we proposed an adaptive QTc (QTcAd) formula that adjusts to subject demographics (i.e., age). Further, we compared the efficacy and accuracy of the QTcAd formula to other widely used alternatives.

Method

Using age as a demographic parameter, we tested the QTcAd formula across diverse age groups with different heart rates (HR) in both humans and guinea pigs. Utilizing retrospective human (n=1360) and guinea pig electrocardiogram (ECG) data from in-vivo (n=55) and ex-vivo (n=66) settings, we evaluated the formula's effectiveness. Linear regression fit parameters of HR-QTc (slope and R²) were utilized for performance assessment. To evaluate the accuracy of the predicted QTc, we acquired epicardial electrical and optical voltage data from Langendorff-perfused guinea pig hearts.

Results

In both human subjects and guinea pigs, the QTcAd formula consistently outperformed other formulae across all age groups. For instance, in a 20-year-old human group (n=300), the QTcAd formula successfully nullified the inverse HR-QT relationship (R²=5.1E-09, slope=-3.5E-05), while the Bazett formula (QTcB) failed to achieve comparable effectiveness (R²= 0.20, slope=0.91). Moreover, the QTcAd formula exhibited better accuracy than the age-specific Benatar formula (QTcBe), which overcorrected QTc (1-week human QT: 263.8±14.8 ms, QTcAd: 263.8±7.3 ms, p=0.62; QTcBe: 422.5±7.3 ms, p<0.0001). The optically measured pseudo-QT interval (143±22.5 ms, n=44) was better approximated by QTcAd (180.6±17.0 ms) compared to all other formulae. Furthermore, we demonstrated that the QTcAd formula was not inferior to individual-specific QTc formulae.

Conclusion

The demography-based QTcAd formula showed superior performance across human and guinea pig age groups, which may enhance the efficacy of QTc for cardiovascular disease diagnosis, risk stratification, and drug safety testing.

What is known

Corrected QT (QTc) is a well-known ECG biomarker for cardiovascular disease risk stratification and drug safety testing. Various QT rate-correction formulae have been developed, but these formulae do not perform consistently across diverse datasets (e.g., sex, age, disease, species).

What the study adds

We introduce a novel QTc formula (QTcAd) that adapts to demographic variability, as the parameters can be modified based on the characteristics of the study population. The formula (QTcAd = QT + (|m|*(HR-HR mean )) - includes the absolute slope (m) of the linear regression of QT and heart rate (HR) and the mean HR of the population (HR mean ) as population characteristics parametersˍUsing datasets from both pediatric and adult human subjects and an animal model, we demonstrate that the QTcAd formula is more effective at eliminating the QT-HR inverse relationship, as compared to other commonly used correction formulae.

Comparison of corrected QT (QTc) interval of electrocardiogram calculated from various formulas

QT interval in an electrocardiogram (ECG) is interpreted after correction (QTc) by various formulas. This study aimed to compare the QTcs calculated by nine formulas. Sinus rhythm ECG reports of 1140 anonymous subjects showed uncorrected QT interval of 388.49 ± 42.74 ms. The QTc calculated by Bazett (443.96 ± 57.58 ms), Fridericia (424.37 ± 50.1 ms), Dmitrienko (433.59 ± 53.37 ms), Framingham (422.59 ± 45.55 ms), Schlamowitz (433.89 ± 48.05 ms), Hodges (421.6 ± 46.4 ms), Ashman (434.33 ± 54.05 ms), Rautaharju (427.75 ± 47.4 ms), and Sarma (429.22 ± 48.67 ms) showed a significant difference F (8, 10251) = 22.78 p < 0.0001. Hence, ECG should contain the formula for proper reporting and ease of interpretation by clinicians.

Electrocardiographic Abnormalities in Nigerian Hypertensives With Echocardiographic Left Ventricular Hypertrophy

Introduction To enhance the diagnosis of anatomic left ventricular hypertrophy (LVH) using electrocardiography (ECG), we aimed to identify common ECG amplitude and non-amplitude abnormalities in Nigerian patients with hypertensive echocardiographic LVH. Method The study included 1,765 patients with essential hypertension aged 18 years and older from the Federal Medical Centre Abuja Hypertension Registry (FMCAHR). Participants underwent echocardiography and ECG following the American College of Cardiology and the American Society of Echocardiography guidelines. Results The prevalence of overall ECG LVH amplitude criteria (43.8%) and individual criteria of Cornell voltage (27.1%), Sokolow-Lyon voltage (23.2%), and Gubner-Ungerleider (13.9%) were higher than non-amplitude ECG abnormalities among patients with echocardiographic LVH. The sensitivity and specificity of LVH criteria were 43.8% and 79.5% for overall ECG LVH, 23.2% and 87.2% for Sokolow-Lyon voltage, 27.1% and 93.3% for Cornell voltage, and 13.9% and 95.4% for Gubner-Ungerleider criteria, respectively. After multivariable adjustment, non-amplitude ECG changes, including prolonged corrected QT (QTc) (odds ratio (OR): 1.68, 95% confidence interval (CI): 1.06-2.66), left ventricular (LV) strain pattern (OR: 1.83, CI: 1.23-2.72), left axis deviation (OR: 1.56, CI: 1.09-2.24), poor R wave progression (OR: 2.36, CI: 1.40-3.97), premature ventricular contractions (OR: 1.80, CI: 1.10-2.91), premature atrial contractions (OR: 2.06, CI: 1.10-3.87), atrial fibrillation (OR: 2.40, CI: 1.20-4.82), and left atrial abnormality (OR: 8.43, CI: 2.95-24.05), were associated with echocardiographic LVH (p < 0.05). Conclusion In our cohort of hypertensive patients, ECG LVH amplitude criteria were the most frequently observed abnormalities associated with echocardiographic LVH. Our findings suggest that despite the low sensitivity, ECG LVH amplitude criteria may remain valuable in diagnosing echocardiographic LVH.

The effect of an anti-malarial herbal remedy, Maytenus senegalensis, on electrocardiograms of healthy Tanzanian volunteers

BACKGROUND

The emergence of resistance to artemisinin-based combination therapy necessitates the search for new, more potent antiplasmodial compounds, including herbal remedies. The whole extract of Maytenus senegalensis has been scientifically investigated for potential biological activities both in vitro and in vivo, demonstrating strong antimalarial activity. However, there is a lack of data on the electrocardiographic effects of M. senegalensis in humans, which is a crucial aspect in the investigation of malaria treatment. Assessing the electrocardiographic effects of M. senegalensis is essential, as many anti-malarial drugs can inadvertently prolong the QT interval on electrocardiograms. Therefore, the study's objective was to evaluate the electrocardiographic effects of M. senegalensis in healthy adult volunteers.

METHODS

This study is a secondary analysis of an open-label single-arm dose escalation. Twelve healthy eligible Tanzanian males, aged 18 to 45, were enrolled in four study dose groups. A single 12-lead electrocardiogram (ECG) was performed at baseline and on days 3, 7, 14, 28, and 56.

RESULTS

No QTcF adverse events occurred with any drug dose. Only one volunteer who received the highest dose (800 mg) of M. senegalensis experienced a moderate transient change (△QTcF > 30 ms; specifically, the value was 37 ms) from baseline on day 28. There was no difference in maximum QTcF and maximum △QTcF between volunteers in all four study dose groups.

CONCLUSIONS

A four-day regimen of 800 mg every 8 h of M. senegalensis did not impact the electrocardiographic parameters in healthy volunteers. This study suggests that M. senegalensis could be a valuable addition to malaria treatment, providing a safer alternative and potentially aiding in the battle against artemisinin-resistant malaria. The results of this study support both the traditional use and the modern therapeutic potential of M. senegalensis. They also set the stage for future research involving larger and more diverse populations to explore the safety profile of M. senegalensis in different demographic groups. This is especially important considering the potential use of M. senegalensis as a therapeutic agent and its widespread utilization as traditional medicine. Trial registration ClinicalTrials.gov, NCT04944966. Registered 30 June 2021-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04944966?term=kamaka&draw=2&rank=1.

Characteristics, predictors and outcomes of new-onset QT prolongation in sepsis: a multicenter retrospective study

BACKGROUND

Sepsis-induced myocardial injury is a serious complication of sepsis. QT prolongation is a proarrhythmic state which reflects myocardial injury in a group of heterogeneous disorders. However, the study on the clinical value of QT prolongation in sepsis is limited.

METHODS

We aimed to investigate the clinical characteristics and predictors of new-onset QT prolongation in sepsis and its impact on the outcome in a multicenter retrospective cohort study. Electrocardiographic and clinical data were collected from patients with sepsis from the wards and intensive care units of four centers after exclusion of QT-influencing medications and electrolyte abnormalities. Clinical outcomes were compared between patients with and without QT prolongation (QTc > 450 ms). Multivariate analysis was performed to ascertain whether QT prolongation was an independent predictor for 30-day mortality. The factors predicting QT prolongation in sepsis were also analyzed.

RESULTS

New-onset QT prolongation occurred in 235/1024 (22.9%) patients. The majority demonstrated similar pattern as type 1 long QT syndrome. Patients with QT prolongation had a higher 30-day in-hospital mortality (P < 0.001), which was also associated with increased tachyarrhythmias including paroxysmal atrial fibrillation or tachycardia (P < 0.001) and ventricular arrhythmia (P < 0.001) during hospitalization. QT prolongation independently predicted 30-day mortality (P = 0.044) after multivariate analysis. History of coronary artery disease (P = 0.001), septic shock (P = 0.008), acute respiratory (P < 0.001), heart (P = 0.021) and renal dysfunction (P = 0.013) were independent predictors of QT prolongation in sepsis.

CONCLUSIONS

New-onset QT prolongation in sepsis was associated with increased mortality as well as atrial and ventricular arrhythmias, which was predicted by disease severity and organ dysfunction.

Prevalence of Increased QTc Dispersion Among Hypertensive Patients and Its Correlation to Clinical Risk Factors: A Hospital-Based Case-Control Study

Background In Ghana and other sub-Saharan African countries, hypertension (HTN) prevalence is rapidly increasing. Hypertensive left ventricular hypertrophy (LVH) is associated with excess fibrous tissue deposition throughout the myocardium. This could lead to ventricular arrhythmias and sudden cardiac death. Increased corrected QT dispersion (QTcd) can cause ventricular repolarization and be used to identify patients at risk of ventricular tachyarrhythmia. The measurement of increased QTcd among hypertensive patients is a simple screening tool to stratify patients at cardiovascular risk. Methods A case-control hospital-based study was conducted on 200 consecutive hypertensive patients. Age- and sex-matched control groups of 200 normotensive individuals who gave informed consent were also recruited. The baseline clinical and demographic characteristics of participants were acquired using structured questionnaires. A physical examination and a resting 12-lead ECG were performed. Increased QTcd and LVH were determined. Results The mean age of hypertensive patients was 50.99±6.73 and 48.19±7.17 for the controls (p-value 0.63). The study population was predominantly female (1:2.4 male:female ratio). Higher mean values for QTcd and LVH (Sokolow-Lyon) were observed among hypertensive patients compared to controls. The prevalence of increased QTcd was 45.0% among hypertensive patients compared to 16.5% in controls (χ2 =38.14, p-value <0.0000001, odds ratio = 4.14). Conclusion Increased QTcd is prevalent among hypertensive Ghanaians. Its measurement can be an effective non-invasive screening tool to risk-stratify hypertensive patients.

Genetic risk factors for drug-induced long QT syndrome: findings from a large real-world case-control study

Aim: Drug-induced long QT syndrome (diLQTS), an adverse effect of many drugs, can lead to sudden cardiac death. Candidate genetic variants in cardiac ion channels have been associated with diLQTS, but several limitations of previous studies hamper clinical utility. Materials & methods: Thus, the purpose of this study was to assess the associations of KCNE1-D85N, KCNE2-I57T and SCN5A-G615E with diLQTS in a large observational case-control study (6,083 self-reported white patients treated with 27 different high-risk QT-prolonging medications; 12.0% with diLQTS). Results: KCNE1-D85N significantly associated with diLQTS (adjusted odds ratio: 2.24 [95% CI: 1.35-3.58]; p = 0.001). Given low minor allele frequencies, the study had insufficient power to analyze KCNE2-I57T and SCN5A-G615E. Conclusion: KCNE1-D85N is a risk factor for diLQTS that should be considered in future clinical practice guidelines.

ANOCA patients with and without coronary vasomotor dysfunction present with limited electrocardiographic remodeling

Background

Coronary vasomotor dysfunction (CVDys) comprises coronary vasospasm (CVS) and/or coronary microvascular dysfunction (CMD) and is highly prevalent in patients with angina and non-obstructive coronary artery disease (ANOCA). Invasive coronary function testing (CFT) to diagnose CVDys is becoming more common, enabling pathophysiologic research of CVDys. This study aims to explore the electrophysiological characteristics of ANOCA patients with CVDys.

Methods

We collected pre-procedural 12-lead electrocardiograms of ANOCA patients with CVS (n = 35), CMD (n = 24), CVS/CMD (n = 26) and patients without CVDys (CFT-, n = 23) who participated in the NL-CFT registry and underwent CFT. Heart axis and conduction times were compared between patients with CVS, CMD or CVS/CMD and patients without CVDys.

Results

Heart axis, heart rate, PQ interval and QRS duration were comparable between the groups. A small prolongation of the QT-interval corrected with Bazett (QTcB) and Fridericia (QTcF) was observed in patients with CVDys compared to patients without CVDys (CVS vs CFT-: QTcB = 422 ± 18 vs 414 ± 18 ms (p = 0.14), QTcF = 410 ± 14 vs 406 ± 12 ms (p = 0.21); CMD vs CFT-: QTcB = 426 ± 17 vs 414 ± 18 ms (p = 0.03), QTcF = 413 ± 11 vs 406 ± 12 ms (p = 0.04); CVS/CMD vs CFT-: QTcB = 424 ± 17 vs 414 ± 18 ms (p = 0.05), QTcF = 414 ± 14 vs 406 ± 12 ms (p = 0.04)).

Conclusions

Pre-procedural 12-lead electrocardiograms were comparable between patients with and without CVDys undergoing CFT except for a slightly longer QTc interval in patients with CVDys compared to patients without CVDys, suggesting limited cardiac remodeling in patients with CVDys.

Comparison of the effects of propofol and alfaxalone on the electrocardiogram of dogs, with particular reference to QT interval

Cardiac electrical activity is often altered by administration of anesthetic drugs. While the effects of propofol in this regard have previously been described in dogs, to date, there are no reports of the effect of alfaxalone. This study investigated the impact of both propofol and alfaxalone on the ECG of 60 dogs, after premedication with acepromazine and methadone. Heart rate increased significantly in both groups. The PR and QRS intervals were significantly increased following propofol while with alfaxalone the QRS duration was significantly increased and ST segment depression was observed. The QT and JT interval were significantly shorter following induction with alfaxalone, but, when corrected (c) for heart rate, QTc and JTc in both groups were significantly greater following induction. When comparing the magnitude of change between groups, the change in RR interval was greater in the alfaxalone group. The change in both QT and JT intervals were significantly greater following alfaxalone, but when QTc and JTc intervals were compared, there were no significant differences between the two drugs. The similarly increased QTc produced by both drugs may suggest comparable proarrhythmic effects.

Electromechanical Window and Spontaneous Ventricular Tachyarrhythmias in Takotsubo Syndrome

QT interval prolongation is common in patients hospitalized with Takotsubo syndrome (TTS), however, only a minority experience ventricular tachyarrhythmias. Our aim was to characterize the electromechanical window (EMW) in patients with TTS and to evaluate its association with ventricular tachyarrhythmias. We preformed aretrospective analysis of 84 patients hospitalized with TTS in the Tel-Aviv Medical Center between 2013 and 2022. All patients underwent a comprehensive echocardiographic evaluation and the EMW was calculated by subtracting the QT interval from the QRS onset to the aortic valve closure obtained from a continuous-wave Doppler for the same beat. Of the 84 patients with TTS, 74 (88%) were female and the mean age was 70 ± 11 years. The mean left ventricular ejection fraction was 42 ± 8%. The EMW was negative in 81 patients (96%), and the mean EMW was -69 ± 50 ms. Ventricular tachyarrhythmias occurred in 7 patients (8%). The EMW of patients who experienced ventricular tachyarrhythmias was more negative than patients who did not (-133 ± 23 ms vs -63 ± 48 ms, p = 0.001). In the univariate analysis, EMW and QT were associated with ventricular tachyarrhythmias (univariate odds ratio [OR]EMW 1.03, 95% confidence interval [CI] 1.01 to 1.05, p = 0.003 and univariate ORQTc 1.02, 95% CI 1.01 to 1.03, p = 0.02); however, only EMW remained significant in the multivariate analysis (OREMW 1.03 95% CI 1.03 to 1.05, p = 0.023). EMW was more effective than corrected QT interval in identifying patients who had ventricular tachyarrhythmias (AUCEMW: 0.89, 95% CI 0.82 to 0.97 vs AUCQTc 0.77, 95% CI 0.61 to 0.93, p = 0.02), and a cut-off value of -108 ms was predictive of ventricular tachyarrhythmias with a sensitivity of 86% and a specificity of 79%. In conclusion, EMW is negative in patients with TTS and is associated with increased risk for ventricular tachyarrhythmias. The role of EMW in the risk stratification of patients with TTS warrants further investigation.

An increase in intercellular crosstalk and electrotonic coupling between cardiomyocytes and nonmyocytes reshapes the electrical conduction in the metabolic heart characterized by short QT intervals in ECGs

Cardiac conduction abnormalities are disorders in metabolic syndrome (MetS), however, their mechanisms are unknown. Although ventricular arrhythmia reflects the changes in QT-interval of electrocardiograms associated with the changes in cardiomyocyte action potential durations (APDs), recent studies emphasize role of intercellular crosstalk between cardiomyocytes and nonmyocytes via passive (electrotonic)-conduction. Therefore, considering the possible increase in intercellular interactions of nonmyocytes with cardiomyocytes, we hypothesized an early-cardiac-remodeling characterized by short QT-interval via contributions and modulations of changes by nonmyocytes to the ventricular APs in an early-stage MetS hearts. Following the feeding of 8-week-old rats with a high-sucrose diet (32%; MetS rats) and validation of insulin resistance, there was a significant increase in heart rate and changes in the electrical characteristics of the hearts, especially a shortening in action potential (AP) duration of the papillary muscles. The patch-clamp analysis of ventricular cardiomyocytes showed an increase in the Na+ -channel currents while there were decreases in  l-type Ca2+ -channel (LTCC) currents with unchanged K+ -channel currents. There was an increase in the phosphorylated form of connexin 43 (pCx43), mostly with lateral localization on sarcolemma, while its unphosphorylated form (Cx43) exhibited a high degree of localization within intercalated discs. A high-level positively-stained α-SMA and CD68 cells were prominently localized and distributed in interfibrillar spaces of the heart, implying the possible contributions of myofibroblasts and macrophages to both shortened APDs and abnormal electrical conduction in MetS hearts. Our data propose a previously unrecognized pathway for SQT induction in the heart. This pathway includes not only the contribution of short ventricular-APDs via ionic mechanisms but also increasing contributions of the electrotonic-cardiomyocyte depolarization, spontaneous electrical activity-associated fast heterogeneous impulse conduction in the heart via increased interactions and relocations between cardiomyocytes and nonmyocytes, which may be an explanation for the development of an SQT in early-cardiac-remodeling.

Prognostic value of ECG monitor findings in COVID-19

AIMS

COVID-19 can cause severe illness and multiorgan dysfunction. Acute myocardial damage has been detected in a significant portion of patients with COVID-19; therefore, several studies have reported that electrocardiographic findings could be used to evaluate the severalty of COVID-19. However, performing standard ECG for each patient hospitalised with COVID-19 can increase the level of exposure to COVID-19 among medical staff. Therefore, this study aimed to investigate the prognostic value of continuous electrocardiographic monitor findings in patients with COVID-19.

METHODS

Among 1612 consecutive patients with COVID-19 who were admitted to our hospital between August 2021 and May 2022, we identified 96 (76±4 years) patients who underwent electrocardiographic monitor during hospitalisation. All electrocardiographic monitors were analysed by two independent cardiologists blinded to the clinical data of the patients. The endpoint was defined as the occurrence of all-cause mortality related to COVID-19. The event data were retrospectively gathered from the patients' medical records. A multivariate Cox model was used to assess whether these electrocardiographic monitor findings and clinical data were associated with in-hospital mortality.

RESULTS

During a mean hospitalisation period of 22.8±3.2 days, in-hospital mortality occurred in 17 (18%) patients. Atrial fibrillation (HR: 3.95, 95% CI: 1.39 to 11.21) and lung disease complications (HR: 2.91, 95% CI: 1.06 to 7.98) were significant prognostic factors for death in multivariate analysis. Compared with the non-complicated lung disease and non-atrial fibrillation group, the risk of mortality was significantly higher in the lung disease complication and atrial fibrillation group in the multivariate Cox proportional model (HR: 8.37, 95% CI: 1.69 to 41.30, p=0.009).

CONCLUSIONS

The simple method of ECG monitor could adequately detect atrial fibrillation. This study demonstrated that atrial fibrillation complicated with lung disease, could have potential prognostic value among patients with COVID-19.

Agreement of Computerized QT and QTc Interval Measurements Between Both Bedside and Expert Nurses Using Electronic Calipers

BACKGROUND

In hospitalized patients, QT/QTc (heart rate corrected) prolongation on the electrocardiogram (ECG) increases the risk of torsade de pointes. Manual measurements are time-consuming and often inaccurate. Some bedside monitors automatically and continuously measure QT/QTc; however, the agreement between computerized versus nurse-measured values has not been evaluated.

OBJECTIVE

The aim of this study was to examine the agreement between computerized QT/QTc and bedside and expert nurses who used electronic calipers.

METHODS

This was a prospective observational study in 3 intensive care units. Up to 2 QT/QTc measurements (milliseconds) per patient were collected. Bland-Altman test was used to analyze measurement agreement.

RESULTS

A total of 54 QT/QTc measurements from 34 patients admitted to the ICU were included. The mean difference (bias) for QT comparisons was as follows: computerized versus expert nurses, -11.04 ± 4.45 milliseconds (95% confidence interval [CI], -2.3 to -19.8; P = .016), and computerized versus bedside nurses, -13.72 ± 6.70 (95% CI, -0.70 to -26.8; P = .044). The mean bias for QTc comparisons was as follows: computerized versus expert nurses, -12.46 ± 5.80 (95% CI, -1.1 to -23.8; P = .035), and computerized versus bedside nurses, -18.49 ± 7.90 (95% CI, -3.0 to -33.9; P = .022).

CONCLUSION

Computerized QT/QTc measurements calculated by bedside monitor software and measurements performed by nurses were in close agreement; statistically significant differences were found, but differences were less than 20 milliseconds (on-half of a small box), indicating no clinical significance. Computerized measurements may be a suitable alternative to nurse-measured QT/QTc. This could reduce inaccuracies and nurse burden while increasing adherence to practice recommendations. Further research comparing computerized QT/QTc from bedside monitoring to standard 12-lead electrocardiogram in a larger sample, including non-ICU patients, is needed.

Atrial fibrillation and QT corrected. What is the best formula to use?

BACKGROUND

QT interval varies with the heart rate (HR), so a correction in QT calculation is needed (QTc). Atrial fibrillation (AF) is associated with elevated HR and beat-to-beat variation.

AIM

To find best correlation between QTc in atrial fibrillation (AF) versus restored sinus rhytm (SR) after electrical cardioversion (ECV) (primary end point) and to determine which correction formula and method are the best to determine QTc in AF (secondary end point).

METHODS

During a 3-month period, we considered patients who underwent 12-lead ECG recording and received an AF diagnosis with indication for ECV. Exclusion criteria were as follows: QRS duration >120 ms, therapy with QT-prolonging drugs, a rate control strategy and a nonelectrical cardioversion. The QT interval was corrected using Bazzett's, Framingham, Fridericia and Hodges formulas during the last ECG during AF and the first one immediately after ECV. QTc mean was calculated as mQTc (average of 10 QTc calculated beat per beat) and as QTcM (QTc calculated from the average of 10 raw QT and RR for each beat).

RESULTS

Fifty consecutive patients were enrolled in the study. Bazett's formula showed a significant change in mean QTc value between the two rhythms (421.5 ± 33.9 vs. 446.1 ± 31.9; p < 0.001 for mQTc and 420.9 ± 34.1 vs. 441.8 ± 30.9; p = 0.003 for QTcM). On the contrary, in patients with SR, QTc assessed by the Framingham, Fridericia, and Hodges formulas was similar to that in AF. Furthermore, good correlations between mQTc and QTcM are present for each formula, even in AF or SR.

CONCLUSIONS

During AF, Bazzett's formula, seems to be the most imprecise in QTc estimation.

Effect of antipsychotic use by patients with schizophrenia on deceleration capacity and its relation to the corrected QT interval

OBJECTIVE

Schizophrenia patients treated with antipsychotics are at higher risk of sudden cardiac death. Decreased deceleration capacity (DC) of the heart rate is an accurate predictor of cardiac mortality. We evaluated the risk of sudden cardiac death due to antipsychotic use by assessing DC and examining the association between DC and the corrected QT interval (QTc) in schizophrenia patients.

METHODS

We measured the DC and QTc of 138 schizophrenia patients. We then compared the DC of 86 age- and sex-matched healthy controls with that of 86 schizophrenia patients. We investigated the correlation of DC of approximately 138 schizophrenia patients with prescribed doses of antipsychotics using linear regression analysis. We compared the DC of schizophrenia patients with and without prolonged QT intervals.

RESULTS

We found DC significantly differed between schizophrenia patients on antipsychotic medication and healthy controls. Additionally, DC was negatively correlated with antipsychotic use, especially chlorpromazine, zotepine, olanzapine and clozapine, in a dose-dependent manner. There was no significant association between DC and the QTc.

CONCLUSION

Assessing DC could facilitate monitoring and identification of increased risk of cardiac mortality in patients with schizophrenia that take antipsychotics. Assessing both DC and the QTc may enhance the accuracy of predicting sudden cardiac death.

Temporal change in repolarization parameters after surgical correction of valvular heart diseases

BACKGROUND

Ventricular tachyarrhythmia is a potentially fatal outcome of cardiac surgery. Abrupt changes in the hemodynamics after surgical correction of valvular heart disease (VHD) can lead to alterations in ventricular repolarization. We compared the difference between temporal changes in repolarization parameters after correction of left-sided VHD.

METHODS

We retrospectively analyzed the electrograms of patients who underwent surgical correction of isolated VHD between 2006 and 2015 at Asan Medical Center, including mitral stenosis (MS), mitral regurgitation (MR), aortic stenosis (AS), and aortic regurgitation (AR). Ventricular repolarization parameters were measured at pre-specified time intervals after index surgery using a custom-made ECG analysis program. We compared repolarization parameters, including QT and corrected QT intervals, T peak-to-end interval, and corrected T peak-to-end interval.

RESULTS

Analysis of 8265 ECGs from 2110 patients (266 MS, 1059 MR, 421 AS, and 364 AR) was performed. Patients with AS were characterized by older age and more comorbidities than other VHDs. The corrected QT interval showed a peak value immediately after surgery and decreased thereafter in the AS groups. However, a gradual increase over 1 month after surgery in AR, MS, and MR groups was observed. The corrected T peak-to-end interval increased in the MS and MR groups and was unchanged in the AS and AR groups.

CONCLUSIONS

The repolarization parameters of surgery changed dynamically after left-sided valvular surgery. Understanding differential temporal change of repolarization parameters according to the type of VHD would help clinicians avoid fatal arrhythmias related to the repolarization changes.

Analysis of the effect of cortisone on the QT interval

BACKGROUND

Cardiac death caused by malignant arrhythmias is very prevalent. Prolongation of the QT interval is a relevant aspect in arrhythmia mechanisms. Prior studies have revealed that the QTc interval could be shortened by cortisone. Moreover, in an animal model of long QT syndrome, cortisone treatment shortens the ventricular action potential duration. The present study investigated the effect of methylprednisolone (MPS) on the QTc interval in cardiovascularly healthy humans.

METHODS

Patients who had just been diagnosed with multiple sclerosis receiving MPS therapy were analysed prospectively. Demographic data, laboratory values, anti-arrhythmic medication and baseline and follow-up ECGs were extracted from the patients' medical records.

RESULTS

Seventy-eight patients were included. The mean ± standard deviation age was 47 ± 15 years. The values of the electrolytes were normal. All patients were treated with MPS for 3 or 5 days. The heart rate increased at the beginning of MPS therapy and decreased during the subsequent period. ECG measurements showed that the QTc interval was prolonged at the beginning of MPS therapy and shortened over the course of treatment. The longest QTc intervals were obtained by calculation with Bazett's formula.

CONCLUSIONS

In humans, cortisone shortens the QTc interval over time. The analysis indicates a cumulative effect of cortisone that lasts longer. The results of our pilot study reveal that cortisone might be added to therapeutic strategies in patients with long QT syndromes. Further clinical studies have to be carried out to analyze potential clinical options.

The influence of different glucose tolerance on QTc interval: a population-based study

BACKGROUND

Corrected QT (QTc) interval has been reported to be associated with type 2 diabetes. This study aimed to explore the relationship between different glucose tolerance and QTc intervals among middle-aged and older Chinese individuals.

METHODS

We conducted a cross-sectional analysis that included 9898 subjects (3194 men and 6704 women) in a Chinese population. Glucose tolerance was studied during the oral glucose tolerance test (OGTT). Insulin, blood pressure, hemoglobin A1c (HbA1c), serum lipids, hepatic transaminases and waist-to-hip ratio were assessed. The QTc interval was derived from ECG recordings, and the subjects were stratified based on different glucose tolerance.

RESULTS

QTc interval levels were increased significantly in the subjects with abnormal glucose metabolism compared with the normal glucose regulation group. Multiple regression analyses showed that the QTc interval was significantly associated with fasting plasma glucose, 2-h OGTT plasma glucose and HbA1c. The odds ratio of prolonged QTc was 1.396 for impaired glucose regulation (IFG)/impaired fasting glucose (IGT) (95% CI 0.126-1.730), and 1.342 for type 2 diabetes (95% CI 0.142-1.577) after all potential confounders were adjusted.

CONCLUSIONS

Impaired glucose tolerance (IGR) and diabetes are associated with prolonged QTc intervals among middle-aged and older Chinese individuals. Abnormal glucose regulation can be used to monitor the QTc interval in the population.

Common ECG Changes and Prognostic Importance of ECG Findings in Covid-19 Patients Presenting to the Emergency Department

Aim: It is known that cardiac involvement may occur in patients with COVID-19 infection. And one of the best diagnostic tools of cardiac involvement is the ECG. The aim of this study is to investigate the common ECG findings in COVID-19 infection and the effect of these findings on the prognosis. Material and Method: 215 patients who applied to our emergency department between 04.06.2022 and 04.08.2022 and met the criteria for inclusion in the study were included in this study. All patient results and ECG images were accessed from the hospital data recording system. The results were used for statistical analysis. Results: Of 215 patients, 118 were female and 97 were male, and the mean age was 58±21 years. Of these patients, 52 were hospitalized in the service and 17 were hospitalized in intensive care units, and 146 patients were discharged from the emergency department. The most common ECG finding was ST-T wave change. It was observed that there was a correlation between the detection of VT in the ECG and the intensive care unit admission. It was observed that the ECG findings of the patients had no effect on the prognosis. Conclusion: All ECG findings can be seen in patients admitted to the emergency department with COVID-19 infection. The most common ECG finding is ST-T wave change. In addition, long QTc, sinus tachycardia and AF are also common. However, no correlation was found between ECG findings and disease prognosis.

Accurate QT correction method from transfer entropy

Background

The QT interval in the electrocardiogram (ECG) is a fundamental risk measure for arrhythmic adverse cardiac events. However, the QT interval depends on the heart rate and must be corrected accordingly. The present QT correction (QTc) methods are either simple models leading to under- or overcorrection, or impractical in requiring long-term empirical data. In general, there is no consensus on the best QTc method.

Objective

We introduce a model-free QTc method-AccuQT-that computes QTc by minimizing the information transfer from R-R to QT intervals. The objective is to establish and validate a QTc method that provides superior stability and reliability without models or empirical data.

Methods

We tested AccuQT against the most commonly used QT correction methods by using long-term ECG recordings of more than 200 healthy subjects from PhysioNet and THEW databases.

Results

AccuQT overperforms the previously reported correction methods: the proportion of false-positives is reduced from 16% (Bazett) to 3% (AccuQT) for the PhysioNet data. In particular, the QTc variance is significantly reduced and thus the RR-QT stability is increased.

Conclusion

AccuQT has significant potential to become the QTc method of choice in clinical studies and drug development. The method can be implemented in any device recording R-R and QT intervals.

Cardiotoxicity drug screening based on whole-panel intracellular recording

Unintended binding of small-molecule drugs to ion channels affects electrophysiological properties of cardiomyocytes and potentially leads to arrhythmia and heart failure. The waveforms of intracellular action potentials reflect the coordinated activities of cardiac ion channels and serve as a reliable means for assessing drug toxicity, but the implementation is limited by the low throughput of patch clamp for intracellular recording measurements. In the last decade, several new technologies are being developed to address this challenge. We recently developed the nanocrown electrode array (NcEA) technology that allows robust, parallel, and long-duration recording of intracellular action potentials (iAPs). Here, we demonstrate that NcEAs allow comparison of iAP waveforms before and after drug treatment from the same cell. This self-referencing comparison not only shows distinct drug effects of sodium, potassium, and calcium blockers, but also reveals subtle differences among three subclasses of sodium channel blockers with sub-millisecond accuracy. Furthermore, self-referencing comparison unveils heterogeneous drug responses among different cells. In our study, whole-panel simultaneous intracellular recording can be reliably achieved with ∼94% success rate. The average duration of intracellular recording is ∼30 min and some last longer than 2 h. With its high reliability, long recording duration, and easy-to-use nature, NcEA would be useful for iAP-based preclinical drug screening.

Homocysteine Levels and Clinical Outcomes in Schizophrenia—A Pilot Randomized Controlled Trial

Background:

There is an increasing need for proactive and individualized responses to various diseases in today’s progressive health-care fraternity. Accordingly, the approach to schizophrenia patients encompasses novel developments in the area of personalized medicine. Antipsychotic drugs in clinical practice necessitate biomarkers for the prediction of treatment outcomes and monitoring to ensure an appropriate choice of duration of chronic therapies. Hence, we studied the relation between homocysteine levels in peripheral blood and the effectiveness as well as the safety of haloperidol and olanzapine in schizophrenia treatment.

Materials and Methods:

A prospective randomized parallel-group open-label interventional clinical trial was conducted on 40 mild to moderate schizophrenia patients. To compare the efficacy of olanzapine and haloperidol Brief Psychiatric Rating Scale (BPRS) score was used. Homocysteine levels of peripheral blood and Abnormal Involuntary Movement Scale scores were evaluated.

Results:

BPRS score improved in both groups on day 14 and day 28. But significantly more with olanzapine ( P value =.001). The olanzapine group showed a higher reduction (13.91±0.47 to 9.74±0.5) in homocysteine levels than the haloperidol group. Also, the BPRS scores negatively correlated ( r = –0.66) to homocysteine levels.

Conclusion:

Therefore, our study shows that peripheral blood homocysteine levels can be used to predict and assess the treatment outcome in schizophrenia patients. Biomarker driven approach in schizophrenia will allow the patients to be treated promptly with the right drug. In this light, personalized treatment holds great potential in the future.

Clozapine Blood Concentration Predicts Corrected QT-Interval Prolongation in Patients With Psychoses

BACKGROUND

Corrected QT-interval (QTc) prolongation (QTP) is a rare but fatal adverse effect of antipsychotics. Clozapine is the only antipsychotic recommended for treatment of resistant schizophrenia; however, clozapine has been reported to cause QTP. We sought factors predictive of QTP in patients who had antipsychotic polypharmacy involving clozapine. We explored whether the clozapine blood concentration might predict QTP.

METHODS

We included 133 patients with schizophrenia spectrum disorder who had antipsychotic polypharmacy involving clozapine. We used the χ2 and nonparametric tests to compare clozapine therapeutic drug monitoring (TDM) values and QTc-prolonged person (QTPP) status. Multivariate regression and mediator models were used to identify risk factors for QTPP status and QTP.

RESULTS

In total, 111 patients were prescribed clozapine. The QTPP rates were 31.3% (20) for men and 23.2% (16) for women. Compared with the non-QTPP group, the QTPP group exhibited significantly higher daily dose of all antipsychotics including clozapine, a higher clozapine dose, and elevated clozapine and norclozapine TDM values. Furthermore, such patients were prescribed a greater number of antipsychotics. Multivariate logistic regression revealed that only the clozapine TDM value could be predictive factor for QTPP status (P = 0.018). A clozapine TDM value above the therapeutic range (>600 mg/dL) was associated with a high risk of QTPP status (adjusted odds ratio, 6.5; 95% confidence interval, 1.7-25.2; P = 0.006). The mediator model revealed that the clozapine TDM values completely mediated the association between the clozapine dose and the QTc interval.

CONCLUSIONS

The clozapine blood concentration reliably predicts QTP in patients with clozapine use.

Frequency of QTc Interval Prolongation in Children and Adults with Williams Syndrome

QTc prolongation (≥ 460 ms), according to Bazett formula (QTcB), has been identified to be increased in Williams syndrome (WS) and suggested as a potential cause of increased risk of sudden cardiac death. The Bazett formula tends to overestimate QTc in higher heart rates. We performed a retrospective chart review of WS patients with ≥ 1 electrocardiogram (EKG) with sinus rhythm, no evidence of bundle branch blocks, and measurable intervals. A total of 280 EKGs from 147 patients with WS were analyzed and 123 EKGs from 123 controls. The QTc was calculated using Bazett formula. The average QTcB for individuals with WS and controls was 444 ± 24 ms and 417 ± 26 ms, respectively (p < 0.001). In our WS cohort 34.4% had at least 1 EKG with a QTcB ≥ 460 ms. The mean heart rate (HR) from patients with WS was significantly higher than controls (96 bpm vs 76 bpm, p < 0.001). Linear regression showed that HR contributed 27% to QTcB prolongation in the patients with WS. Patients with WS have a mean QTcB in the normal range but higher than controls, and a higher than expected frequency of QTc ≥ 460 ms compared to the general population. HR is also higher in WS and contributes modestly to the WS QTcB prolongation. Future studies are needed to assess if these findings contribute risk to sudden cardiac death but in the interim we recommend routine EKG testing, especially when starting QTc prolonging medications.

Importance of Formula-Specific Centile Thresholds for Evaluation of Heart Rate-Corrected QT Prolongation in Williams Syndrome

Patients with Williams syndrome (WS) have a 25- to 100-fold higher risk of sudden death and prolonged heart rate-corrected QT (QTc). A recent study using the Fridericia formula for QT correction suggested that prolongation is principally an issue of heart rate. We used multiple published heart rate correction formulas to reevaluate the prevalence of QTc prolongation in our original dataset from our 2010 study at the Children's Hospital of Philadelphia. The ninety-eighth centile for QTc and corrected JT Interval (JTc) of the control population for each formula were used to set the threshold for prolongation. Prevalence comparison was done with Fisher's exact test. Predictors of longer QTc/JTc were assessed using linear regression models adjusting for age, gender, and heart rate. Adjusted odds of QTc/JTc prolongation were evaluated with conditional logistic regression models matched based on age and heart rate. There were 482 electrocardiograms from 188 patients with WS and 1,522 from normal controls. Patients with WS were younger, with higher heart rates and shorter RR and QRS intervals. WS was associated with longer QTc/JTc compared with controls. There were higher odds of prolonged QTc/JTc in patients with WS than controls using both Bazett and Fridericia formulas. In conclusion, this study confirms the higher prevalence of QTc prolongation in WS compared with controls and highlights the importance of setting appropriate formula-specific upper thresholds for QTc prolongation for accurate diagnosis.

Electrocardiography and heart rate variability in Göttingen Minipigs: Impact of diurnal variation, lead placement, repeatability and streptozotocin-induced diabetes

BACKGROUND

The Göttingen Minipig is widely used in preclinical research and safety pharmacology, but standardisation of porcine electrocardiography (ECG) is lacking. The aim of this study was to investigate diurnal effects, change over time and choice of lead on ECG morphology and heart rate variability (HRV) in healthy and streptozotocin (STZ) induced diabetic Göttingen Minipigs.

METHODS

Diabetes was experimentally induced using STZ in 11 Göttingen Minipigs (DIA). Seven controls (CON) were included. 24-h ECG was recorded at baseline and four months. Morphological parameters (QRS and T wave duration, P- and T-wave amplitude, PR and QT (Bazett's (QTcb) or Fridericia (QTcf) correction) intervals and ST segment), presence of cardiac arrhythmias, heart rate (HR) and HRV (time and frequency domain) were analysed.

RESULTS

Four months after induction, DIA had decreased P-wave amplitude (P < 0.0001) and T-wave duration (P = 0.017), compared to CON. QTcb was lower in DIA, but not in CON. Both groups had decreased HR (P < 0.0001) and QRS duration (lead II, P = 0.04) and length of PR-segment increased (lead I and II, P < 0.01) while selected HRV parameters also increased (all P < 0.01). Time of day influenced HR, QRS duration, PR segment, ST segment, T- and P-wave amplitude and some parameters of HRV. Inter- and intra-observer variability of morphological measurements was low (<6%).

CONCLUSION

ECG parameters were influenced by time setting, diurnal variation and lead. Some ECG and HRV changes were found in diabetic minipigs four months after STZ induction. The findings underline the need for standardisation of ECG and HRV in Göttingen Minipigs.

Analysis of athlete QT intervals by age: Fridericia and Hodges heart rate corrections outperform Bazett for athlete ECG screening

BACKGROUND

Cardiac screening of elite athletes including a 12‑lead electrocardiogram (ECG) is recommended by numerous international bodies. Current athlete ECG interpretation guidelines recommend the Bazett method to correct the QT interval (QTc).

OBJECTIVE

This study sought to investigate normative QTc changes by age using athlete screening ECGs and different QT correction methods in a population of elite cricketers.

METHODS

Initial cardiac screening ECGs from an existing database of elite Australian cricketers aged 14-35 years were examined. Average QT interval, QTcB (corrected QT-Bazett), QTcF (Fridericia), QTcH (Hodges), and heart rate (HR) were analyzed by age and sex.

RESULTS

A total of 1310 athletes (66% male, 34% female) were included with mean age 19.1 years and mean heart rate 66.9 bpm (range 38-121 bpm). With increasing age, HR decreased and absolute QT increased. The pattern of QTc change with age differed depending on the method of correction: Bazett correction (QTcB) demonstrated a "dish-shaped" or broad U-shaped appearance; while Fridericia and Hodges corrections showed a linear increase in QTc from young to older age. The Bazett method had a stronger correlation of HR with QTc (R² = 0.32) than either Fridericia (R² = 0.0007) or Hodges (R² = 0.009) methods.

CONCLUSIONS

The Bazett method is not the most accurate QT correction in athletes, especially during adolescence. In elite cricketers, QTcB revealed a drop in QTc from adolescence to early adulthood due to mis-correction of the QT interval. The Fridericia method has the smoothest correction of HR and least QT variation by age and may be preferred for athlete screening.

Associations between electrocardiogram and carotid ultrasound parameters: a healthy chinese group study

Background: Electrocardiogram (ECG) and carotid ultrasound (CUS) are important tools for the diagnosis and prediction of cardiovascular disease (CVD). This study aimed to investigate the associations between ECG and CUS parameters and explore the feasibility of assessing carotid health with ECG.

Methods: This cross-sectional cohort study enrolled 319 healthy Chinese subjects. Standard 12-lead ECG parameters (including the ST-segment amplitude [STA]), CUS parameters (intima-media thickness [IMT] and blood flow resistance index [RI]), and CVD risk factors (including sex, age, and systolic blood pressure [SBP]) were collected for analysis. Participants were divided into the high-level RI group (average RI ≥ 0.76, n = 171) and the normal RI group (average RI < 0.76, n = 148). Linear and stepwise multivariable regression models were performed to explore the associations between ECG and CUS parameters.

Results: Statistically significant differences in sex, age, SBP, STA and other ECG parameters were observed in the normal and the high-level RI group. The STA in lead V₃ yielded stronger significant correlations (r = 0.27–0.42, p < 0.001) with RI than STA in other leads, while ECG parameters yielded weak correlations with IMT (|r| ≤ 0.20, p < 0.05). STA in lead V₂ or V₃, sex, age, and SBP had independent contributions (p < 0.01) to predicting RI in the stepwise multivariable models, although the models for IMT had only CVD risk factors (age, body mass index, and triglyceride) as independent variables. The prediction model for RI in the left proximal common carotid artery (CCA) had higher adjusted R² (adjusted R² = 0.31) than the model for RI in the left middle CCA (adjusted R² = 0.29) and the model for RI in the right proximal CCA (adjusted R² = 0.20).

Conclusion: In a cohort of healthy Chinese individuals, the STA was associated with the RI of CCA, which indicated that ECG could be utilized to assess carotid health. The utilization of ECG might contribute to a rapid screening of carotid health with convenient operations.

[Corrected QT interval and GRACE score relationship in patients with non-ST segment elevation myocardial infarction]

Background

The Global Registry of Acute Coronary Events (GRACE) prediction model stratifies patients with non-ST-segment elevation myocardial infarction (NSTEMI). Corrected QT interval (QTc) is not considered in this model.

Objective

To evaluate the relationship between the QTc interval and the GRACE score in patients with NSTEMI.

Materials and methods

An observational, retrospective study was carried between 2016 and 2019. We included patients with diagnosis of NSTEMI, QTc intervals were calculated with Bazett's formula, and they were classified into 2 groups: a normal QTc interval (<440 ms) and prolonged (≥440 ms). According to the GRACE score they were classified in three ranges: low risk (≤109 points), intermedium (110 - 139 points) and high (≥140 points), we determined if there were a correlation between QTc interval and the GRACE score.

Results

A total of 940 patients with a diagnosis of NSTEMI were admitted in our institution, 634 met the inclusion criteria, there were 390 patients with normal QTc interval and 244 with a prolonged QTc interval. Patients with prolonged QTc were older (65.5 vs 61, p=0.001) with a lower proportion of males (71.7% vs 82.8%, p=0.001). An association was found between the GRACE score and the QTC interval, subjects with a normal QTc had a greater proportion of low and intermediate risk than those with a prolonged QTc (p=0.001). Conclusions. In NSTEMI patients, a normal QTc interval (<440 ms) is associated with a GRACE risk score of low or intermediate risk.

QT Interval Prolongation Is a Novel Predictor of 1-Year Mortality in Patients With COVID-19 Infection

Background

QT interval prolongation is common in critically ill patients and is associated with increased mortality. However, the predictive value of a prolonged corrected QT interval (QTc) for myocardial injury and long-term mortality among patients hospitalized with COVID-19 infection is not well known.

Purpose

To evaluate the association of prolonged QTc with myocardial injury and with 1-year mortality among patients hospitalized with COVID-19 infection.

Materials and Methods

A total of 335 consecutive patients hospitalized with COVID-19 infection were prospectively studied. All patients underwent a comprehensive echocardiographic evaluation within 48 h from admission. Using the Bazett formula, the QTc interval was calculated from the first ECG tracing recorded at the ER. QTc ≥ 440 ms in males and ≥450 ms in females was considered prolonged. Patients with elevated cardiac biomarkers and/or echocardiographic signs of myocardial dysfunction were considered to have myocardial injury. The predictive value of QTc prolongation for myocardial injury was calculated using a multivariate binary regression model. One-year mortality rate of patients with and without QTc prolongation was compared using the log-rank test, and a multivariate Cox regression model adjusting for multiple covariates was performed to evaluate the 1-year mortality risk.

Results

One-hundred and nine (32.5%) patients had a prolonged QTc. Compared to patients without QTc prolongation, patients with prolonged QTc were older (70 ± 14.4 vs. 62.7 ± 16.6, p < 0.001), had more comorbidities, and presented with a more severe disease. Prolonged QTc was an independent predictor for severe or critical disease (adjusted HR 2.14, 95% CI 1.3-3.5; p = 0.002) and myocardial injury (adjusted HR 2.07, 95% CI 1.22-3.5; p = 0.007). One-year mortality of patients with prolonged QTc was higher than those with no QTc prolongation (40.4% vs. 15.5; p < 0.001). Following adjustment to multiple covariates including myocardial injury and disease severity, QTc prolongation was found to be associated with increased 1-year mortality risk (HR 1.69, 95% CI 1.06-2.68, p = 0.027).

Conclusion

Prolonged QTc is associated with disease severity, myocardial injury and 1-year mortality among patients hospitalized with COVID-19 infection.

Declining Levels and Bioavailability of IGF-I in Cardiovascular Aging Associate With QT Prolongation-Results From the 1946 British Birth Cohort

Background

As people age, circulating levels of insulin-like growth factors (IGFs) and IGF binding protein 3 (IGFBP-3) decline. In rat cardiomyocytes, IGF-I has been shown to regulate sarcolemmal potassium channel activity and late sodium current thus impacting cardiac repolarization and the heart rate-corrected QT (QTc). However, the relationship between IGFs and IGFBP-3 with the QTc interval in humans, is unknown.

Objectives

To examine the association of IGFs and IGFBP-3 with QTc interval in an older age population-based cohort.

Methods

Participants were from the 1946 Medical Research Council (MRC) National Survey of Health and Development (NSHD) British birth cohort. Biomarkers from blood samples at age 53 and 60-64 years (y, exposures) included IGF-I/II, IGFBP-3, IGF-I/IGFBP-3 ratio and the change (Δ) in marker levels between the 60-64 and 53y sampled timepoints. QTc (outcome) was recorded from electrocardiograms at the 60-64y timepoint. Generalized linear multivariable models with adjustments for relevant demographic and clinical factors, were used for complete-cases and repeated after multiple imputation.

Results

One thousand four hundred forty-eight participants were included (48.3% men; QTc mean 414 ms interquartile range 26 ms). Univariate analysis revealed an association between low IGF-I and IGF-I/IGFBP-3 ratio at 60-64y with QTc prolongation [respectively: β -0.30 ms/nmol/L, (95% confidence intervals -0.44, -0.17), p < 0.001; β-28.9 ms/unit (-41.93, -15.50), p < 0.001], but not with IGF-II or IGFBP-3. No association with QTc was found for IGF biomarkers sampled at 53y, however both ΔIGF-I and ΔIGF-I/IGFBP-3 ratio were negatively associated with QTc [β -0.04 ms/nmol/L (-0.08, -0.008), p = 0.019; β -2.44 ms/unit (-4.17, -0.67), p = 0.007] while ΔIGF-II and ΔIGFBP-3 showed no association. In fully adjusted complete case and imputed models (reporting latter) low IGF-I and IGF-I/IGFBP-3 ratio at 60-64y [β -0.21 ms/nmol/L (-0.39, -0.04), p = 0.017; β -20.14 ms/unit (-36.28, -3.99), p = 0.015], steeper decline in ΔIGF-I [β -0.05 ms/nmol/L/10 years (-0.10, -0.002), p = 0.042] and shallower rise in ΔIGF-I/IGFBP-3 ratio over a decade [β -2.16 ms/unit/10 years (-4.23, -0.09), p = 0.041], were all independently associated with QTc prolongation. Independent associations with QTc were also confirmed for other previously known covariates: female sex [β 9.65 ms (6.65, 12.65), p < 0.001], increased left ventricular mass [β 0.04 ms/g (0.02, 0.06), p < 0.001] and blood potassium levels [β -5.70 ms/mmol/L (-10.23, -1.18) p = 0.014].

Conclusion

Over a decade, in an older age population-based cohort, declining levels and bioavailability of IGF-I associate with prolongation of the QTc interval. As QTc prolongation associates with increased risk for sudden death even in apparently healthy people, further research into the antiarrhythmic effects of IGF-I on cardiomyocytes is warranted.

Practical Approaches to Antipsychotic-Associated Corrected QT Interval Prolongation in Patients With Serious Mental Illness: A Review of Cases

BACKGROUND

There is no consensus for assessment and management of patients with serious mental illness (SMI) who are at risk for cardiac morbidity and mortality due to antipsychotic-associated QTc prolongation.

OBJECTIVE

The objective of this review was to assess methods for risk scoring, QT correction calculation, and clinical management in SMI patients with antipsychotic-associated QTc prolongation.

METHODS

A search was performed in PubMed for case reports that described QTc prolongation in adult patients with schizophrenia or bipolar disorder prescribed an antipsychotic. Reports published in North America between 2000 and 2020 were eligible. The Mayo, Tisdale, and RISQ-PATH scoring tools were applied to cases to categorize risk level.

RESULTS

Seventeen cases were included. Most patients were prescribed a second-generation antipsychotic for schizophrenia, with baseline and maximum QTc values of 429 milliseconds and 545 milliseconds, respectively. The Mayo scoring tool identified 17 (100%) cases as "high risk," Tisdale identified 9 (53%) cases as "moderate risk" and 7 (41%) cases as "low risk," while RISQ-PATH identified 9 (53%) cases as "not low risk" and 8 (47%) cases as "low risk." Three cases reported the QT correction formula utilized (18%). The most common intervention to address antipsychotic-associated QTc prolongation was switching to a different antipsychotic (35%). Approximately one third of patients experienced Torsades de Pointes.

CONCLUSION

There is a lack of standardization for antipsychotic-associated QTc prolongation risk assessment and management in patients with SMI. This review provides real-world data representing actual clinical practice.

Examination of New Electrocardiographic Repolarization Markers in Diabetic Patients with Noncritical Coronary Artery Disease

Background

Diabetes mellitus (DM) is a multisystemic, chronic disease that affects many organs. Coronary artery disease (CAD) is the leading cause of death in patients with DM. The electrocardiogram's new ventricular repolarization parameters can predict mortality and morbidity. The ventricular repolarization indices were examined in diabetic patients with a CAD diagnosis in this study.

Methods

The study group consisted of 84 DM patients (51 males; mean age 58.8 ± 6.6) with noncritical CAD. The control group consisted of 84 DM patients (47 males; mean age 58.7 ± 8.8) with a normal coronary artery. The intervals of QT, QRS, JT, and Tp-e were all measured. Tp-e/QT, Tp-e/QTc, Tp-e/JT, and Tp-e/JTc ratios were determined with QTc, QTd, QTdc, and JTc intervals.

Results

Heart rate (74.4 ± 13.1 vs. 70.0 ± 13.6 bpm, p: 0.036), QT (381.0 ± 30.3 vs. 368.6 ± 29.1 ms, p: 0.008), QTc (407.5 (359-450) vs. 389 (339-430) ms, p < 0.001), QTd (25.1 ± 6.2 vs. 21.9 ± 9.9 ms, p: 0.013), QTdc (26.7 ± 6.1 vs. 23.1 ± 10.8 ms, p: 0.010), Tp-e (95.7 ± 12.2 vs. 73.6 ± 9.8 ms, p < 0.001), JT (293.8 ± 22.0 vs. 283.5 ± 30.9 ms, p: 0.014), and JTc (313.6 ± 12.3 vs. 302.4 ± 33.7 ms, p=0.005) intervals, and Tp-e/QT (0.25 ± 0.03 vs. 0.20 ± 0.03 ms, p < 0.001), Tp-e/QTc [0.23 (0.19-2.33) vs. 0.19 (0.14-0.25) ms, p=0.007], Tp-e/JT (0.33 ± 0.04 vs. 0.26 ± 0.04 ms, p < 0.001), and Tp-e/JTc (0.30 ± 0.03 vs. 0.24 ± 0.03 ms, p < 0.001) ratios were all found to be significantly higher in diabetic patients with noncritical CAD.

Conclusion

In this study, ventricular repolarization markers on the surface ECG were found to be elevated in diabetic CAD patients. These variables may be related to fatal arrhythmic events. To be sure, large-scale, randomized controlled trials are required.

The best QT correction formula in a non-hospitalized population: the Fasa PERSIAN cohort study

Background

QT interval as an indicator of ventricular repolarization is a clinically important parameter on an electrocardiogram (ECG). QT prolongation predisposes individuals to different ventricular arrhythmias and sudden cardiac death. The current study aimed to identify the best heart rate corrected QT interval for a non-hospitalized Iranian population based on cardiovascular mortality.

Methods

Using Fasa PERSIAN cohort study data, this study enrolled 7071 subjects aged 35–70 years. Corrected QT intervals (QTc) were calculated by the QT interval measured by Cardiax® software from ECGs and 6 different correction formulas (Bazett, Fridericia, Dmitrienko, Framingham, Hodges, and Rautaharju). Mortality status was checked using an annual telephone-based follow-up and a minimum 3-year follow-up for each participant. Bland–Altman, QTc/RR regression, sensitivity analysis, and Cox regression were performed in IBM SPSS Statistics v23 to find the best QT. Also, for calculating the upper and lower limits of normal of different QT correction formulas, 3952 healthy subjects were selected.

Results

In this study, 56.4% of participants were female, and the mean age was 48.60 ± 9.35 years. Age, heart rate in females, and QT interval in males were significantly higher. The smallest slopes of QTc/RR analysis were related to Fridericia in males and Rautaharju followed by Fridericia in females. Thus, Fridericia’s formula was identified as the best mathematical formula and Bazett’s as the worst in males. In the sensitivity analysis, however, Bazett’s formula had the highest sensitivity (23.07%) among all others in cardiac mortality. Also, in the Cox regression analysis, Bazett’s formula was better than Fridericia’s and was identified as the best significant cardiac mortality predictor (Hazard ratio: 4.31, 95% CI 1.73–10.74, p value = 0.002).

Conclusion

Fridericia was the best correction formula based on mathematical methods. Bazett’s formula despite its poorest performance in mathematical methods, was the best one for cardiac mortality prediction. Practically, it is suggested that physicians use QTcB for a better evaluation of cardiac mortality risk. However, in population-based studies, QTcFri might be the one to be used by researchers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02502-2.

Risk assessment tools for QT prolonging pharmacotherapy in older adults: a systematic review

Purpose

Many drugs are associated with the risk of QT prolongation and torsades de pointes (TdP), and different risk assessment tools (RATs) are developed to help clinicians to manage related risk. The aim of this systematic review was to summarize the evidence of different RATs for QT prolonging pharmacotherapy.

Methods

A systematic review was conducted using PubMed and Scopus databases. Studies concerning risk assessment tools for QT prolonging pharmacotherapy, including older adults, were included. Screening and selection of the studies, data extraction, and risk of bias assessment were undertaken.

Results

A total of 21 studies were included, involving different risk assessment tools. Most commonly used tools were risk scores (n = 9), computerized physician order entry systems (n = 3), and clinical decision support systems (n = 6). The tools were developed mainly for physicians and pharmacists. Risk scores included a high number of risk factors, both pharmacological and non-pharmacological, for QT prolongation and TdP. The inclusion of patients’ risk factors in computerized physician order entry and clinical decision support systems varied.

Conclusion

Most of the risk assessment tools for QT prolonging pharmacotherapy give a comprehensive overview of patient-specific risks of QT prolongation and TdP and reduce modifiable risk factors and actual events. The risk assessment tools could be better adapted to different health information systems to help in clinical decision-making. Further studies on clinical validation of risk assessment tools with randomized controlled trials are needed.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00228-022-03285-3.

Prediction of sudden cardiac arrest in the general population: Review of traditional and emerging risk factors

Sudden cardiac death (SCD) is the most common and devastating outcome of sudden cardiac arrest (SCA), defined as an abrupt and unexpected cessation of cardiovascular function leading to circulatory collapse. The incidence of SCD is relatively infrequent for individuals in the general population, in the range of 0.03-0.10% per year. Yet, the absolute number of cases around the world is high due to the sheer size of the population at risk, making SCA/SCD a major global health issue. Based on conservative estimates, there are at least 2 million cases of SCA occurring worldwide on a yearly basis. As such, identification of risk factors associated with SCA in the general population is an important objective from a clinical and public health standpoint. This review will provide an in-depth discussion of established and emerging factors predictive of SCA/SCD in the general population beyond coronary artery disease and impaired left ventricular ejection fraction. Contemporary studies evaluating the association between age, sex, race, socioeconomic status and the emerging contribution of diabetes and obesity to SCD risk beyond their role as atherosclerotic risk factors will be reviewed. In addition, the role of biomarkers, particularly electrocardiographic ones, on SCA/SCD risk prediction in the general population will be discussed. Finally, the use of machine learning as a tool to facilitate SCA/SCD risk prediction will be examined.

Estimation of cardiac QTc intervals in people prescribed antipsychotics: a comparison of correction factors

BACKGROUND

A prolonged electrocardiogram (ECG) QT interval is associated with cardiac events and increased mortality. Antipsychotics can prolong the QT interval. The QT interval requires correction (QTc) for heart rate using a formula or QT-nomogram. The QT and QTc can be calculated automatically by the ECG machine or manually; however, machine-measured QT(c) intervals may be inaccurate.

OBJECTIVE

We aimed to investigate the mean QTc and proportion of prolonged QTc intervals in people taking antipsychotic medicines.

METHODS

We conducted an observational retrospective chart review and data analysis of all consecutive patients taking antipsychotics, with an ECG record, admitted to the psychiatric unit of a large tertiary hospital in Brisbane, Australia, between 1 January 2017 and 30 January 2019. We investigated the mean QTc of people taking antipsychotics to determine differences using (a) machine versus manual QT interval measurement and (b) QTc correction formulae (Bazett, Fridericia, Framingham, Hodges and Rautaharju) and the QT-nomogram. We also determined the number of people with a prolonged QTc using different methods and compared rates of prolonged QTc with antipsychotic monotherapy and polypharmacy.

RESULTS

Of 920 included people, the mean (±SD) machine-measured, Bazett-corrected QT interval (recorded from the ECG) was 435 ms (±27), significantly longer (p < 0.001) than the mean manually measured corrected QT intervals with Fridericia 394 ms (±24), Framingham 395 ms (±22), Hodges 398 ms (±22) and Rautaharju 400 ms (±24) formulae. There were significantly more people with a prolonged QTc using machine-measured QT and the Bazett formula (12.0%, 110/920) when compared with manually measured QT and the Fridericia formula (2.2%, 20/920) or QT-nomogram (0.7%, 6/920). Rates of QTc prolongation did not differ between people taking antipsychotic polypharmacy compared with monotherapy.

CONCLUSION

Machine-measured QTc using the Bazett formula overestimates the QTc interval length and number of people with a prolonged QTc, compared with other formulae and the QT-nomogram. We recommend manually measuring the QT and correcting with the Fridericia formula or QT-nomogram prior to modifying antipsychotic therapies.

Splitting the P-Wave: Improved Evaluation of Left Atrial Substrate Modification after Pulmonary Vein Isolation of Paroxysmal Atrial Fibrillation

Atrial substrate modification after pulmonary vein isolation (PVI) of paroxysmal atrial fibrillation (pAF) can be assessed non-invasively by analyzing P-wave duration in the electrocardiogram (ECG). However, whether right (RA) and left atrium (LA) contribute equally to this phenomenon remains unknown. The present study splits fundamental P-wave features to investigate the different RA and LA contributions to P-wave duration. Recordings of 29 pAF patients undergoing first-ever PVI were acquired before and after PVI. P-wave features were calculated: P-wave duration (PWD), duration of the first (PWDon-peak) and second (PWDpeak-off) P-wave halves, estimating RA and LA conduction, respectively. P-wave onset (PWon-R) or offset (PWoff-R) to R-peak interval, measuring combined atrial/atrioventricular and single atrioventricular conduction, respectively. Heart-rate fluctuation was corrected by scaling. Pre- and post-PVI results were compared with Mann–Whitney U-test. PWD was correlated with the remaining features. Only PWD (non-scaling: Δ=−9.84%, p=0.0085, scaling: Δ=−17.96%, p=0.0442) and PWDpeak-off (non-scaling: Δ=−22.03%, p=0.0250, scaling: Δ=−27.77%, p=0.0268) were decreased. Correlation of all features with PWD was significant before/after PVI (p<0.0001), showing the highest value between PWD and PWon-R (ρmax=0.855). PWD correlated more with PWDon-peak (ρ= 0.540–0.805) than PWDpeak-off (ρ= 0.419–0.710). PWD shortening after PVI of pAF stems mainly from the second half of the P-wave. Therefore, noninvasive estimation of LA conduction time is critical for the study of atrial substrate modification after PVI and should be addressed by splitting the P-wave in order to achieve improved estimations.

Splitting the P-Wave: Improved Evaluation of Left Atrial Substrate Modification after Pulmonary Vein Isolation of Paroxysmal Atrial Fibrillation

Atrial substrate modification after pulmonary vein isolation (PVI) of paroxysmal atrial fibrillation (pAF) can be assessed non-invasively by analyzing P-wave duration in the electrocardiogram (ECG). However, whether right (RA) and left atrium (LA) contribute equally to this phenomenon remains unknown. The present study splits fundamental P-wave features to investigate the different RA and LA contributions to P-wave duration. Recordings of 29 pAF patients undergoing first-ever PVI were acquired before and after PVI. P-wave features were calculated: P-wave duration (PWD), duration of the first (PWDon-peak) and second (PWDpeak-off) P-wave halves, estimating RA and LA conduction, respectively. P-wave onset (PWon-R) or offset (PWoff-R) to R-peak interval, measuring combined atrial/atrioventricular and single atrioventricular conduction, respectively. Heart-rate fluctuation was corrected by scaling. Pre- and post-PVI results were compared with Mann-Whitney U-test. PWD was correlated with the remaining features. Only PWD (non-scaling: Δ=-9.84%, p=0.0085, scaling: Δ=-17.96%, p=0.0442) and PWDpeak-off (non-scaling: Δ=-22.03%, p=0.0250, scaling: Δ=-27.77%, p=0.0268) were decreased. Correlation of all features with PWD was significant before/after PVI (p<0.0001), showing the highest value between PWD and PWon-R (ρmax=0.855). PWD correlated more with PWDon-peak (ρ= 0.540-0.805) than PWDpeak-off (ρ= 0.419-0.710). PWD shortening after PVI of pAF stems mainly from the second half of the P-wave. Therefore, noninvasive estimation of LA conduction time is critical for the study of atrial substrate modification after PVI and should be addressed by splitting the P-wave in order to achieve improved estimations.

The missing link: Unlocking the power of cardiac rhythm monitoring device based QT interval detection

Background

The QT interval is of high clinical value as QT prolongation can lead to Torsades de Pointes (TdP) and sudden cardiac death. Insertable cardiac monitors (ICMs) have the capability of detecting both absolute and relative changes in QT interval. In order to determine feasibility for long‐term ICM based QT detection, we developed and validated an algorithm for continuous long‐term QT monitoring in patients with ICM.

Methods

The QT detection algorithm, intended for use in ICMs, is designed to detect T‐waves and determine the beat‐to‐beat QT and QTc intervals. The algorithm was developed and validated using real‐world ICM data. The performance of the algorithm was evaluated by comparing the algorithm detected QT interval with the manually annotated QT interval using Pearson's correlation coefficient and Bland Altman plot.

Results

The QT detection algorithm was developed using 144 ICM ECG episodes from 46 patients and obtained a Pearson's coefficient of 0.89. The validation data set consisted of 136 ICM recorded ECG segments from 76 patients with unexplained syncope and 104 ICM recorded nightly ECG segments from 10 patients with diabetes and Long QT syndrome. The QT estimated by the algorithm was highly correlated with the truth data with a Pearson's coefficient of 0.93 (p < .001), with the mean difference between annotated and algorithm computed QT intervals of −7 ms.

Conclusions

Long‐term monitoring of QT intervals using ICM is feasible. Proof of concept development and validation of an ICM QT algorithm reveals a high degree of accuracy between algorithm and manually derived QT intervals.

Improving the accuracy of estimating blood calcium concentration in Holstein cows using electrocardiographic variables

We previously reported the possibility of using the electrocardiogram variable to estimate blood calcium (Ca) concentration in dairy cows based on the strong positive correlation between the blood Ca concentration and the inverse of the corrected ST peak interval (STc^-1). To improve the accuracy of the estimation of blood Ca concentration, we investigated the relationship between blood Ca concentration and STc^-1 for each postpartum day and available variables other than STc^-1. We measured multiple variables (milk yield, calving number, age, body temperature, etc.), including serum total Ca concentration (tCa), blood ionized Ca concentration (iCa) and STc^-1 in 462 Holstein cows on days 0, 1, 2, 3, 5, and 7 postpartum. A very high correlation was observed between iCa and tCa. The association between tCa and STc^-1 for each postpartum day had a high coefficient of determination of 0.61-0.79 postpartum 0-2 days but decreased after the third day. In the investigation using the data from postpartum days 0-2, STc^-1, heart rate interval, calving number, and age were highly correlated with tCa. In addition, a multiple regression equation was obtained with tCa as the objective variable and STc^-1 and calving number as explanatory variables. The estimation accuracy was improved as compared with the simple regression equation using only STc^-1 as the explanatory variable. This multiple regression equation was used for 11 cows suspected of having hypocalcemia, and it was able to correctly detect cows requiring early treatment, except for one cow.

Population Pharmacokinetic and Concentration-QTc Analysis of Delamanid in Pediatric Participants with Multidrug-Resistant Tuberculosis

A population pharmacokinetic analysis of delamanid and its major metabolite DM-6705 was conducted to characterize the pharmacokinetics of delamanid and DM-6705 in pediatric participants with multidrug-resistant tuberculosis (MDR-TB). Data from participants between the ages of 0.67 and 17 years, enrolled in 2 clinical trials, were utilized for the analysis. The final data set contained 634 delamanid and 706 DM-6705 valid plasma concentrations from 37 children. A transit model with three compartments best described the absorption of delamanid. Two-compartment models for each component with linear elimination were selected to characterize the dispositions of delamanid and DM-6705, respectively. The covariates included in the model were body weight on the apparent volume of distribution and apparent clearance (for both delamanid and DM-6705); formulation (dispersible versus film-coated tablet) on the mean absorption time; age, formulation, and dose on the bioavailability of delamanid; and age on the fraction of delamanid metabolized to DM-6705. Based on the simulations, doses for participants within different age/weight groups that result in delamanid exposure comparable to that in adults following the approved adult dose were calculated. By concentration-QTc (QTcB [QT corrected by Bazett’s formula]) analysis, a significant positive correlation was detected with concentrations of DM-6705. However, the model-predicted upper bounds of the 90% confidence intervals of ΔQTc values were <10 ms at the simulated maximum concentration (C_max) of DM-6705 following the administration of the maximum doses simulated. This suggests that the effect on the QT interval following the proposed dosing is unlikely to be clinically meaningful in children with MDR-TB who receive delamanid.