Diseases and drugs causing prolongation of the QT interval

Repolarization in systemic sclerosis: a meta-analysis

OBJECTIVES

Systemic sclerosis (SSc) is a rare connective tissue disease characterized by immune dysregulation, vascular damage, and increased deposition of extracellular matrix. In SSc, cardiac manifestations are common and account for 14% of deaths. Numerous studies have examined electrocardiographic findings in SSc patients yielding conflicting reports regarding QTc duration. We conducted a systematic review and meta-analysis of existing studies to investigate whether QTc duration may aid in diagnosis and risk stratification of SSc patients.

METHODS

Two electronic databases (PubMed and Embase) were searched for case-control and cohort studies assessing QTc duration in SSc patients published before March 1, 2021. A random-effects model was used to meta-analyze the results, and included studies were tested for heterogeneity. Linear regression was performed to determine correlations between comorbidities, and QTc duration.

RESULTS

Ninety-six studies, abstracts, and posters were identified. After abstract review and duplicate removal, 23 manuscripts remained. After application of the inclusion and exclusion criteria, 10 studies remained which were quantitatively analyzed. The weighted mean QTc was found to be 422.21 ms for SSc patients and 411.43 ms for control subjects. A significant increase in QTc duration among SSc patients was found, with a standardized mean difference of 0.59 (p < 0.01, 95% CI 0.27-0.92). No significant correlation was found between underlying traits and QTc values. Substantial heterogeneity was found between the studies (I² = 83%, p < 0.01).

CONCLUSION

A significant increase in QTc duration is observed in SSc patients, though the absolute prolongation is not extreme. Therefore, the clinical utility of this finding is unclear and merits large prospective observations. Key Points • A statistically significant prolongation of the QTc interval exists in patients with systemic sclerosis. • Absolute QTc differences between healthy controls and scleroderma patients are not extreme, and, as such, may be of limited clinical utility. • When assessing the underlying traits of systemic sclerosis patients, no statistically significant correlations were found between underlying parameters and QTc duration.

Heart Rate Variability in Children With Autism Spectrum Disorder and Associations With Medication and Symptom Severity

Decreased heart rate variability (HRV) is considered a common marker of autonomic dysfunction that contributes to poor health outcomes. While some studies have suggested that children with autism spectrum disorder (ASD) show reduced HRV, research is yet to consider whether this may be associated with medication use and symptom severity. This study examined the relationship between resting state HRV, medication use and symptom severity in children diagnosed with ASD. Children with ASD (N = 86), aged between 3 and 12 years (M = 8.09), were compared to 44 neurotypical children of similar age (M = 7.15). Laboratory assessment of HRV involved 5 min of non-invasive baseline electrocardiogram assessments while participants viewed an age-appropriate non-verbal animated video. Time-domain and frequency-domain HRV measures were analyzed. ASD symptom severity was assessed using the Autism Diagnostic Observation Schedule-Second Edition (ADOS-2) and Social Responsiveness Scale (SRS-2). Results indicated that children with ASD exhibited reduced resting HRV relative to neurotypical children. Subsequent analyses within the ASD group suggested that this group difference was greater in children who were taking psychotropic medication (N = 36). Our data also provides tentative evidence of a relationship between HRV and social impairment symptoms in children with ASD, with more severe repetitive behaviors (as measured by the ADOS-2) associated with decreased resting HRV. Overall, these findings suggest that HRV may be atypical in children with ASD and suggest the importance of exploring HRV as a risk factor for cardiovascular health in this group. LAY SUMMARY: Cardiac activity, such as heart rate variability (HRV), can provide insight into the autonomic nervous system. This study reports on the association between resting-state HRV and autonomic nervous system activity in young children with autism spectrum disorder (ASD) compared to neurotypical children. These results may help us understand what underlies autonomic nervous system dysfunction and the potential pathophysiological mechanisms leading to increased cardiovascular risk in ASD.

Cardiologic side effects of psychotropic drugs

Psychotropic drugs can produce cardiovascular side effects associated with a degree of cardiotoxicity. The coexistence of a heart disease complicates the management of mental illness, can contribute to a reduced quality of life and a worse illness course. The co-occurrence of psychiatric disorders in cardiac patients might affect the clinical outcome and morbidity. Moreover, the complex underlying mechanism that links these two conditions remains unclear. This paper discusses the known cardiovascular complications of psychotropic drugs and analyzes the important implications of antidepressive treatment in patients with previous cardiac history.

Electrocardiographic changes after dipyridamole infusion in patients undergoing myocardial perfusion imaging

OBJECTIVES

Although the diagnostic and prognostic importance of perfusion defects has been clearly established, the meaning of the development and characteristics of electrocardiographic (ECG) changes during dipyridamole infusion is less well defined. This study tries to evaluate the prevalence and significance of ECG changes after dipyridamole infusion and their relation to ischemia in myocardial perfusion single-photon emission computed tomography (SPECT).

METHODS

Two hundred patients underwent 2-day dipyridamole stress/rest Tc-99m-sestamibi myocardial perfusion SPECT. Basal and post dipyridamole ECGs were analyzed. Myocardial perfusion images were interpreted visually and semiquantitatively.

RESULTS

New ECG changes were noted in 20.2% of cases and consisted of 1.1% T-wave flattening, 1.1% T-wave inversion and 14.8% ST depression and 4.2% psuedonormalization. Abnormal ECG changes were noted after dipyridamole infusion in approximately 27.7% of patients with and 14.3% of patients without reversible defect in myocardial perfusion SPECT. A new ST depression was noted in lateral leads in 72.2% of new ST changes. The mean post-dipyridamole heart rate increment in patients with reversible or partially reversible defects was significantly lesser than in patients with normal myocardial perfusion SPECT. In addition, the corrected QT interval (QTc) increment in patients with reversible defects was significantly more than in patients with fixed defects; however, there was no difference when compared with patients with no defects. Using linear regression model, the severity of ST depression and QTc increment were significant predictors of summed difference score. Sensitivity, specificity, and negative and positive predictive values of ST-segment depression for the diagnosis of ischemia were 20.2, 89.5, 60.7, and 58.4%, respectively.

CONCLUSION

The most common ECG change seen after dipyridamole infusion is ST-segment depression. The new ST-segment depression after dipyridamole infusion is highly specific for ischemia. Reversible defects are associated with a lesser increment in heart rate, whereas QTc increment and severity of ST segment depression were significant predictors of summed difference score.

Impact of liver transplantation on rate-corrected QT interval and myocardial function in children with chronic liver disease*

Prolonged QTc interval (>440 ms) is a common abnormality in adult patients with CLD and has been reported to predict patient survival. In this study, 88 children who underwent evaluation for LT, including a 12-lead electrocardiogram and echocardiogram included to determine the frequency of QTc prolongation and related factors in children with CLD and the effect of LT on these factors. Sixty-nine healthy, age- and sex-matched children served as controls. QTc interval was prolonged in 40 CLD patients (45.4%). It was found to be related to PELD score and presence of portal hypertension. Mean QTc was higher in patients who died prior to LT than in the survivors without LT. Mortality risk was increased 3.66-fold in patients with prolonged QTc (p = 0.001, 95% CI: 2-7.2). Cox regression analysis showed that only PELD score was an independent predictor of survival (p = 0.001, beta = -0.41, 95% CI: 5.58-1.82). Five of 48 transplanted children died within three months post-transplant; QTc was not related to post-transplant survival (p = 0.27). QTc normalized in 63.8% patients after LT. After LT, LAD, LVEF, and LVPWT decreased. In conclusion, QTc prolongation is common in children with CLD and associated with high mortality. It may be useful for assessment of the severity of CLD and for the timing for transplantation.

Relationship between the QTc interval at hospital admission and the severity of the underlying ischaemia in low and intermediate risk people studied for acute chest pain

BACKGROUND

The corrected QT interval (QTc) is prolonged in the setting of acute coronary artery disease. However, very little data are available concerning the relationship between the QTc obtained soon after an episode of acute chest pain (ACHP) and the magnitude and severity of the myocardial ischaemia objectified in subsequent stress tests (STS).

METHODS

This was a prospective and observational study in which we investigated the relationship between the QTc determined on the hospital admission electrocardiogram (AQTc) using Bazett's formula and the results of the STS performed subsequently in 206 patients consecutively admitted to the Emergency Department for ACHP without persistent ST-elevation.

RESULTS

The mean AQTc was 456+/-60 ms. There were 88 (42%) individuals with a moderately or severely abnormal STS. The AQTc was longer in the patients with a moderately or severely abnormal STS: 490+/-52 versus 430+/-56 (p<0.001) and was correlated with the probability of the patient having a moderately or severely abnormal STS (c=0.84; p<0.001). The best cut-off point was 450 ms (sensitivity, specificity and negative predictive value: 81, 77 and 84 %). Patients with AQTc>or=450 had a higher frequency of moderately or severely abnormal STS (73 versus 16%; OR: 2.9; 95% CI: 2.1-4.1; p<0.001). After adjusting for age, sex, cardiac risk factors, cardiac history, QRS duration, ST-depression, troponin I release and pre-STS medical treatment, AQTc>or=450 remained as an independent predictor (OR: 12; 95% CI: 6-24; p<0.001).

CONCLUSIONS

In patients studied for ACHP, the QTc on the hospital admission electrocardiogram correlates with the underlying myocardial ischaemia. AQTc>or=450 ms selects a group of people at risk of presenting a moderately or severely abnormal STS, regardless of ST abnormalities and troponin release.

The effects of quinidine and its chiral isolates on erg-1sm potassium current and correlation with gastrointestinal augmentation

Smooth-muscle erg 1 (erg1-sm) potassium channel has been recently reported to participate in the modulation of gastrointestinal contractility. Because quinidine inhibits cardiac potassium channel and as a result augments gastrointestinal contractility, it was thought that quinidine may affect erg1-sm. Studies were undertaken to evaluate the effects of quinidine and its chiral isolates on gastrointestinal erg1-sm potassium current and correlate these effects with colon contractility. Chiral separation (high-performance liquid chromatography technique), mass spectrometry, and optical rotation determination were performed to obtain chiral isolates needed for experiments. The erg1-sm potassium channel was expressed in Xenopus oocytes, and the two-electrode patch clamp technique was employed for recording. An isolated rat colon preparation was employed to measure changes in contractility. As a result of chiral separation, two peaks were obtained with elution times of 8.31 and 8.66 minutes, both with a molecular weight of 324; the optical rotations of racemate isolates X and Y were: +258 degrees, +/-0 degrees; and +217 degrees, respectively. The percentage changes in amplitudes of colon contraction (from baseline) were determined at different concentrations of quinidine and for the two isolates in five experiments in each group. Quinidine 0.1, 1, and 10 microM increased contractility by 79 +/- 34, 125 +/- 42, and 217 +/- 51 (P < or = 0.05); for isolate X, the values were 70 +/- 20, 115 +/- 32, and 272 +/- 32 (P < or = 0.05), and for isolate Y the values were 22 +/- 12, 46 +/- 17, and 59 +/- 22. The inhibition of erg1-sm currents by quinidine was 19 +/- 4, 21 +/- 5, and 48 +/- 6 (P < or = 0.05), respectively; that by isolate X was 20 +/- 4, 23 +/- 5, and 39 +/- 7 (P < or = 0.05), and that by isolate Y was 22 +/- 4, 21 +/- 4, and 31 +/- 6. One chiral isolate and quinidine markedly augmented contractility, whereas quinidine and the two chiral isolates inhibited the erg1-sm potassium currents to a similar extent. These results suggest that erg1-sm inhibition does not explain gastrointestinal contractile augmentation caused by the quinidine racemate and its chiral isolates.

Torsade de pointes associated with the administration of intravenous haloperidol:a review of the literature and practical guidelines for use

Haloperidol is the most commonly used medication for the treatment of delirium and psychosis in the critically ill patient. Whilst generally considered to be safe, haloperidol has been associated with a number of important cardiovascular side effects. The major toxicities include hypotension, cardiac arrhythmias and prolongation of the corrected QT (QTc) interval. In particular, torsade de pointes, a polymorphic ventricular tachyarrhythmia, has been associated with both intravenous and oral haloperidol administration. The management of torsade de pointes consists of discontinuation of the possible offending agent(s), correction of electrolyte abnormalities, administration of magnesium sulfate and, if necessary, overdrive pacing. Although clinicians should be aware of this potentially lethal complication of intravenous haloperidol therapy, it should not deter clinicians from using intravenous haloperidol to treat acute agitation in the critically ill patient with a normal QTc.

The effect of ST resolution on QT dispersion after interventional treatment in acute myocardial infarction

BACKGROUND

It has been reported that reperfusion treatment reduces QT dispersion (QTD) in cases of acute myocardial infarction (AMI). Successful myocardial perfusion is not synonymous with Thrombolysis in Myocardial Infarction (TIMI) III flow. It has been demonstrated that in AMI, the grade of ST-resolution correlates strongly with left ventricular (LV) function, enzyme elevation, and mortality after primary angioplasty.

HYPOTHESIS

This study investigated the relation between ST-resolution grade and QTD and the feasibility of using QTD as a determinant of successful myocardial tissue perfusion in patients in whom TIMI III flow in the infarct-related artery (IRA) is restored by interventional treatment for AMI.

METHODS

The study included 57 patients (38 men, 19 women, average age 54.4 +/- 11.6 years), whose IRA was perfused by primary angioplasty after the diagnosis of anterior AMI with ST elevation. Electrocardiograms of patients were taken 45 +/- 12 min post procedure, and patients were divided into three groups depending on the grade of ST resolution: Group 1, full ST resolution; Group 2, partial ST resolution; and Group 3, unsuccessful ST resolution.

RESULTS

Full ST resolution was seen in 19 cases (33%), partial resolution in 26 cases (47%), and unsuccessful resolution in 12 cases (20%). There were no differences among groups in terms of risk factors, stent diameters, symptom onset-balloon time, LV function, and preprocedure corrected QTD (QTcD) (p = 0.274). After the procedure, a significant reduction in QTcD was found within the groups (p = 0.0001 in Group 1, p = 0.004 in Group 2, and p = 0.011 in Group 3). Reductions in QTcD post procedure were 24.21 +/- 14.27, 11.85 +/- 16.18, and 12.50 +/- 11.58 ms in Groups 1, 2, and 3, respectively. There was a statistically significant difference of p = 0.015 between Groups 1 and 2 and a difference of p = 0.028 between Groups 1 and 3. There was no statistically significant difference between Groups 2 and 3 (p = 0.916).

CONCLUSION

In acute MI, TIMI III flow led to a reduction in QTcD, and full myocardial perfusion made an additional contribution to the electrical stability of the myocardium.

QT interval, cardiovascular risk factors and risk of death in diabetes

A prolonged QT interval is considered an indicator of increased risk of malignant ventricular arrhythmias and/or sudden death. It has been proposed that autonomic neuropathy in diabetes is related to QT interval prolongation and increased mortality rates. Several studies in Type 1 and Type 2 diabetic patients have confirmed the independent relation between prolonged QT interval duration or increased QT interval dispersion and chronic ischemic heart disease. It has been consistently shown that autonomic neuropathy is related to QT interval duration while more controversies exist on the association with QT interval dispersion. In recent years, studies have confirmed the value of QT interval as a predictor of total mortality in both diabetic and non-diabetic subjects. Moreover, several studies have shown a significant relation between QT interval prolongation and cardiovascular disease risk factors. QT interval could be used to stratify the cardiovascular risk in diabetic patients. We still do not know why QT interval is prolonged and how this abnormality leads to death. Nevertheless, QT interval is a simple, low-cost measure, easily obtainable without the need of the patient's compliance and which could help to select patients who need second level diagnostic procedures and strict observation.

Prolongation of QTc interval: relationship with etiology and severity of liver disease, mortality and liver transplantation

BACKGROUND

A prolonged QTc interval has been reported in patients with liver disease. The objectives of our study were to determine whether a prolonged QTc interval was an independent predictor of mortality in patients with cirrhosis and to examine the effect of liver transplantation (LT) on QTc interval.

PATIENTS AND METHODS

We retrospectively studied two cohorts of patients - QTc interval was measured in 409 patients (pre-transplant group), and in 162 patients (transplant group) before and 6 months after LT. QT interval (mean) corrected (QTc) for ventricular rate was read from a 12-lead EKG. Patients with known cardiovascular disease or other risk factors that are known to cause a prolonged QTc interval were excluded.

RESULTS

Pre-transplant group. One hundred and sixty-two patients (40%) had a prolonged QTc interval (>440 ms). By binary logistic regression, age (P=0.005), alcoholic cirrhosis (P=0.007) and Child-Pugh scores (P=0.007) were independent predictors of prolonged QTc interval. Sixty-six patients died during a mean follow-up of 8.9 years. Although the Kaplan-Meier survival curve showed a lower survival in patients with a prolonged QTc interval (P=0.03 by log rank test), when survival was adjusted for the Child-Pugh score by Cox regression survival analysis, there were no survival differences in patients with and without prolonged QTc interval. Cox regression analysis showed that the Child-Pugh score (hazard ratio 1.5, CI 1.3-1.6, s<0.001) was the only independent predictor of survival. Transplant group. In this cohort, 91 patients (56%) had prolonged QTc (>440 ms) before LT. Mean QTc improved significantly after LT (429 +/- 29 ms vs. 450 +/- 39 ms P<0.002). Of the 91 patients with prolonged QTc, 50 (55%) normalized, three (3.3%) remained unchanged, 12 (13.3%) showed further prolongation, and 26 (28%) showed improvement but remained above normal limits. An additional nine patients who had normal QTc before LT developed prolonged QTc (>440 ms) after LT.

CONCLUSION

A prolonged QTc interval was common in patients with cirrhosis, but its presence had no independent effect on mortality. Prolonged QTc returns to normal values in about half of the patients after LT, suggesting that liver disease plays a role, but may not be the only factor in the pathogenesis of prolonged QTc.

Clinical relevance and management of drug-related QT interval prolongation

Much attention recently has focused on drugs that prolong the QT interval, potentially leading to fatal cardiac dysrhythmias (e.g., torsade de pointes). We provide a detailed review of the published evidence that supports or does not support an association between drugs and their risk of QT prolongation. The mechanism of drug-induced QT prolongation is reviewed briefly, followed by an extensive evaluation of drugs associated with QT prolongation, torsade de pointes, or both. Drugs associated with QT prolongation are identified as having definite, probable, or proposed associations. The role of the clinician in the prevention and management of QT prolongation, drug-drug interactions that may occur with agents known to affect the QT interval, and the impact of this adverse effect on the regulatory process are addressed.

Torsade de pointes associated with the administration of intravenous haloperidol

Torsade de pointes is a malignant dysrhythmia that has been reported in a variety of clinical settings and associated with several pharmacologic agents. Patients with a prolonged QTc for heart rate are at higher risk for the development of this arrhythmia. We review the literature supporting the relationship of haloperidol to the development of this malignant dysrhythmia. Clinicians in the critical care setting should be aware of potentially lethal drug-induced ventricular tachydysrhythmias such as torsade de pointes.

Increased QTc dispersion and mortality in uremic patients with acute myocardial infarction

QT dispersion (the difference between maximum and minimum QT across the 12-lead electrocardiogram [ECG]), which reflects regional variations in ventricular repolarization, is a predictor of arrhythmia and cardiovascular mortality. The present study was undertaken to assess the difference in QT dispersion between uremic and nonuremic patients with acute myocardial infarction (AMI) and its relationship to post-AMI clinical outcome. Twelve-lead ECG recordings were obtained the first and third days after the onset of AMI in 21 uremic and 21 nonuremic patients. QT intervals were measured on 12-lead ECGs and corrected by heart rate (QTc). Our findings show that uremic patients with AMI had greater QTc dispersion (84 +/- 35 versus 55 +/- 15 milliseconds; P < 0.001), a greater 1-year mortality rate (48% versus 18%; P = 0.003), and underwent fewer reperfusion therapies (5 of 21 versus 17 of 21 patients; P = 0.002) compared with nonuremic patients with AMI. Patients with AMI who died had greater QTc dispersion than those who survived (102 +/- 40 versus 67 +/- 40 milliseconds; P = 0.015). An optimal QTc dispersion cutoff value of 60 milliseconds had a sensitivity of 100% and specificity of 55% in predicting 1-year mortality in uremic patients with AMI. Uremic patients with AMI administered thrombolytic therapies (n = 5) had reduced 1-year mortality rates (0% versus 63%; P = 0.003) and shortened QTc dispersion from days 1 to 3 (changes in QTc dispersion between days 1 and 3, 29% +/- 9% decrease versus 13% +/- 5% increase; P = 0.001) compared with those without therapies (n = 16). Our findings suggest that greater QT dispersion is associated with greater total mortality, and thrombolytic therapies could reduce QTc dispersion and mortality in uremic patients with AMI. It is prudent to refine our current management regimen for uremic patients with AMI to improve the poor clinical outcome.

Prolonged QTc interval and its relationship to autonomic cardiovascular reflexes in patients with cirrhosis

BACKGROUND/AIMS

We have previously shown that an abnormality in cardiac autonomic reflexes (AN) is an independent predictor of mortality in patients with chronic liver disease. Aim of this study was to determine whether there was an association between prolonged QTc interval and cardiac AN.

METHODS

Cardiac AN and QTc interval were determined in 130 patients (Child A 42, B 53, C 35) with alcoholic and non-alcoholic liver disease.

RESULTS

Prolonged QTc (>440ms) was seen in 58 (Child A 30%, B 46%, C 60%, P=0.04) patients. Autonomic tests were normal in 21%, borderline abnormal in 36% and definitely abnormal in 43%. QTc correlated with albumin (P<0.001), prothrombin time (P=0.003) and Child-Pugh score (P<0.001), but not with Valsalva ratio, heart rate variation with 6 breath/min breathing, tilt table or isometric exercise. By logistic regression analysis, QTc correlated only with Child-Pugh score (P<0.001). Mean QTc of 34 who died during the follow up was higher than survivors. Cox regression analysis showed that only Child-Pugh score and AN were independent predictors of mortality.

CONCLUSIONS

Prolonged QTc seen in liver disease is independent of their cardiac autonomic function, but is related to the severity of the liver disease.

The association between intravenous haloperidol and prolonged QT interval

Although intravenous haloperidol (HAL) is an effective medication that is often prescribed to treat agitation, several instances of torsade de pointes or prolonged QT interval have been reported. To investigate the association between intravenous HAL and QT prolongation and between intravenous HAL and ventricular tachyarrhythmia, a cross-sectional cohort study was performed that included measuring corrected QT intervals (QTc) on an emergency basis before intravenous HAL and continuously monitoring electrocardiographic (ECG) findings after intravenous HAL. During a 2-month period, 47 patients received intravenous injections to control psychotic disruptive behavior. According to clinical practice, patients were divided as follows. The FZ-alone group was treated with intravenous flunitrazepam (FZ), and the FZ-plus-HAL group received intravenous FZ followed by intravenous HAL. Although the difference in the mean QTc immediately after intravenous FZ between the two groups was not significant, the mean QTc after 8 hours in the FZ-plus-HAL group was longer than that in the FZ-alone group (p < 0.001). Four patients in the FZ-plus-HAL group had a QTc of more than 500 msec after 8 hours. The change in QTc during 8 hours significantly differed between the two groups (t = 2.64, p > 0.05). Furthermore, the change in QTc was moderately correlated with the dose of intravenous HAL, as evidenced by a coefficient of correlation of 0.48 (p < 0.001). However, ventricular tachyarrhythmia was not detected among 307 patients within a 1-year period, although the ECG was continuously monitored for at least 8 hours after intravenous HAL. The modest nature of QTc prolongation and the apparent absence of ventricular tachyarrhythmia under continuous ECG monitoring indicate that QTc prolongation associated with intravenous HAL is not necessarily dangerous. However, in an emergency situation, clinicians cannot exclude patients predisposed to torsade de pointes, such as those with inherited ion channel disorders. Therefore, clinicians should be aware of the association between intravenous HAL and QT prolongation.

Is the QT interval an indicator of autonomic state?

Prolonged QT interval is suggested to indicate an increased risk of sudden cardiac death in certain clinical conditions such as diabetes mellitus. We investigated whether the individual QT interval is an indicator of an autonomic state. An ambulatory 24-hour ECG was recorded in 53 subjects from different clinical backgrounds. Power spectral components of heart rate variability (HRV) and the QT interval were regressively obtained at a heart rate of 60, 70, 80, 90, or 100 beats per minutes (bpm). Log values of the high-frequency component of HRV (HF: 0.15-0.50 Hz, a scale of cardiac parasympathetic tone) failed to show a relationship with the QT interval. In contrast, the QT interval at a heart rate of 90 bpm and 100 bpm showed a significant correlation with the log values of the low-frequency component (LF: 0.04-0.15 Hz) and the log[LF/HF], i.e., a putative scale of sympathetic tone (100 bpm: QT vs logLF: r = 0.414, p < 0.005, QT vs log[LF/HF]: 0.416, p < 0.002). Also, attenuated rate-dependent QT shortening was associated with greater logLF and log[LF / HF] values at a heart rate of 80, 90, or 100 bpm. These results suggest that the QT interval at a moderate heart rate (approximately 90-100 / min) and the degree of rate-dependent QT shortening are related to individual sympathetic tone.

Prolonged QT interval in acute psychotic patients

Some recent clinical studies indicate that hypokalemia is characteristic for acute psychotic patients at the time of emergency admission. As hypokalemia is one of the major causes for prolonged QT interval, it was hypothesized that acute psychotic patients could show prolonged QT interval. Sixty-seven drug-free, acute psychotic patients were evaluated for corrected QT (QTc) interval, as well as demographic and clinical characteristics at the time of emergency admission. The mean QTc interval of psychiatric emergency patients was prolonged, and the mean QTc interval of psychiatric emergency patients was longer than that of psychiatric outpatients (t=5.20, P<0.0001). Age- or gender-related difference, circadian fluctuation of QT interval, medication, concomitant disease, obesity, and serum electrolytes except potassium were not major causes. There was a significant negative correlation as evidenced by a coefficient of correlation of -0.28 (P<0.05). As psychiatric emergency patients often receive parenteral antipsychotics, which may have adverse effects on prolonged QT interval, paying attention to QT interval might have some clinical significance on emergency admission.

QT dispersion in patients with chronic heart failure: beta blockers are associated with a reduction in QT dispersion

OBJECTIVE

To compare QT dispersion in patients with impaired left ventricular systolic function and in matched control patients with normal left ventricular systolic function.

DESIGN

A retrospective, case-control study with controls matched 4:1 for age, sex, previous myocardial infarction, and diuretic and beta blocker treatment.

SETTING

A regional cardiology centre and a university teaching hospital.

PATIENTS

25 patients with impaired left ventricular systolic function and 100 patients with normal left ventricular systolic function.

MAIN OUTCOME MEASURES

QT and QTc dispersion measured by three methods: the difference between maximum and minimum QT and QTc intervals, the standard deviation of QT and QTc intervals, and the "lead adjusted" QT and QTc dispersion.

RESULTS

All measures of QT/QTc dispersion were closely interrelated (r values 0.86 to 0.99; all p < 0.001). All measures of QT and QTc dispersion were significantly increased in the patients with impaired left ventricular systolic function v controls (p < 0.001): 71.9 (6.5) (mean (SEM)) v 46.9 (1.7) ms for QT dispersion, and 83.6 (7.6) v 54.3 (2.1) ms(-1-2) for QTc dispersion. All six dispersion parameters were reduced in patients taking beta blockers (p < 0.05), regardless of whether left ventricular function was normal or impaired-by 9.4 (4.6) ms for QT dispersion (p < 0.05) and by 13.8 (6. 5) ms(-1-2) for QTc dispersion (p = 0.01).

CONCLUSIONS

QT and QTc dispersion are increased in patients with systolic heart failure in comparison with matched controls, regardless of the method of measurement and independently of possible confounding factors. beta Blockers are associated with a reduction in both QT and QTc dispersion, raising the possibility that a reduction in dispersion of ventricular repolarisation may be an important antiarrhythmic mechanism of beta blockade.

Relationship between QT dispersion and the incidence of early ventricular arrhythmias in patients with acute myocardial infarction

There is controversy about the influence of QT dispersion on the incidence of early ventricular arrhythmias in patients with acute myocardial infarction (AMI). The QT and QTc dispersion (QTd, QTcd) between two groups of patients with AMI were compared: 39 patients with early sustained ventricular tachycardia or ventricular fibrillation (VT/VF) and 40 patients without such arrhythmias. QTd and QTcd were calculated from the admission and predischarge ECG, expressed as the difference between the maximum and minimum QT and QTc interval in 12 leads. The coefficient of variability was also calculated (VQT, VQTc). Groups did not differ significantly in age, incidence of previous infarction, Killip class, electrolyte status, infarct location, expected and final ECG infarct size, enzymatic infarct size, thrombolytic treatment and reperfusion rate, i.e., in variables that could influence the VT/VF occurrence. On admission, patients with VT/VF had significantly greater QTd (77+/-23 vs 53+/-27 ms, P<0.001) and QTcd (90+/-29 vs 62+/-28 ms, P<0.001); VQT and VQTc were also significantly higher. Although similar differences existed on predischarge ECG, they were smaller. The results indicate that QT dispersion varies during the illness, and that measurements of QT dispersion could be helpful in predicting serious ventricular arrhythmias.

Long QTc and torsades de pointes in human immunodeficiency virus disease

Three patients with human immunodeficiency virus (HIV) infection presented with QT, prolongation (> 440 ms) and torsades de pointes. We sought to evaluate the etiology of the long QT syndrome in these patients without previously identified causes for QT, prolongation, and determine the prevalence among patients with HIV infection. The three index patients underwent: (1) left stellate ganglion block; (2) beta-blocker challenge; and (3) electrocardiographic stress testing. QTc interval was measured before and after intervention. We undertook a retrospective analysis of prevalence of QTC prolongation among all patients with computerized ECGs over a 6-month period at one institution and compared it to the prevalence in hospitalized patients with HIV disease. Thirty-four thousand one hundred eighty-one patients with computerized ECGs were screened for QTc prolongation. Forty-two hospitalized patients with HI disease had computerized ECG during the same 6-month period. In the three index patients, the QTc failed to shorten with left stellate ganglion blockade, beta-blocker challenge, or stress testing, suggesting an acquired form of the long QT syndrome in these patients with HIV disease. None had previously recognized acquired causes of QT, prolongation. Mexiletine hydrochloride was useful in preventing recurrences of torsades de pointes. We observed a 7.0% prevalence of QT, prolongation among all patients screened. Hospitalized patients with HIV disease (n = 42) during this same period, demonstrated an increased prevalence of QT, prolongation (28.6%, P = 0.002). Patients with HIV disease have a significantly higher prevalence of QTc prolongation than a general hospital-based population, may have an unrecognized acquired form of the long QT syndrome, and are at risk for torsades de pointes.

Syncope: current diagnosis and treatment

The patient with syncope often poses a formidable diagnostic challenge. A large number of underlying causes must be considered, ranging in severity from benign to life-threatening. A careful, systematic clinical evaluation beginning with a history, physical examination, and ECG will establish the diagnosis in most patients, and the judicious use of specialized testing will confirm or uncover the cause in many of the remaining cases. Further basic and clinical research into the pathogenesis and treatment of neurocardiogenic syncope, the role of HUT testing in neurally mediated syncope, and the optimal use of EPS in patients with cardiac disease will markedly improve our management of these patients in the future.

Relationships between electrocardiographic and echocardiographic findings in systemic sclerosis (scleroderma)

We assessed the prevalence of electrocardiographic abnormalities in patients with systemic sclerosis and evaluated their functional significance through a comparison with echocardiographic findings. Seventy-two patients with systemic sclerosis and 64 controls underwent resting electrocardiogram (ECG) and M-mode, two-dimensional, Doppler and color Doppler echocardiography. Electrocardiographic abnormalities were observed in 48.7% of patients. Conduction disturbances (27.7%) infarction pattern (13.8%), non-specific ST-T wave changes (13.8%) and right ventricular hypertrophy (11.1%) were the most frequent abnormalities. QTc interval was significantly longer in patients with systemic sclerosis than in controls. Significant differences between patients and controls were found in the prevalence of long QTc interval (p = 0.0016) infarction pattern (p = 0.0016), right ventricular hypertrophy (p = 0.007) and non-specific ST-T wave abnormalities (p = 0.0016). All patients with infarction pattern and 90% of patients with prolonged QTc interval had some echocardiographic abnormalities. Electrocardiographic signs of right ventricular hypertrophy were 16% sensitive and 93% specific for pulmonary hypertension; the sensitivity and specificity of the combination of right ventricular hypertrophy, right atrial enlargement and right bundle branch block were 35% and 90%, respectively. Standard ECG is useful to assess cardiac involvement in patients with systemic sclerosis. If infarction pattern, right ventricular hypertrophy or long QTc interval are present, a cardiac involvement is very likely.

QT interval-heart rate relation during exercise in normal men and women: definition by linear regression analysis

OBJECTIVES

This study sought to develop a regression-based method for characterization of QT interval behavior during exercise and to define the normal range of the resulting "dynamic" measures of repolarization during submaximal treadmill testing in men and women.

BACKGROUND

The Bazett-corrected QT (QTc) interval during exercise has been used as a marker for ischemic disease, arrhythmogenic substrate and the long QT syndrome. However, recent studies indicate that the QTc interval is nonlinear with respect to heart rate during exercise, making the end-exercise QTc interval dependent on peak work load achieved. In contrast, the unadjusted QT interval measured from QRS onset to T wave offset (QTo) and from QRS onset to T wave peak (QTm) appears to vary linearly with heart rate during gently graded effort.

METHODS

The QT interval relation to heart rate and cycle length was examined by linear regression in 50 normal men (mean age 48 years) and 30 normal women (mean age 51 years), all of whom had normal rest electrocardiograms. The QTo and QTm measurements were made from digitized lead V5 complexes averaged by computer over 20-s periods, at upright control and after seven 2-min stages of the Cornell modification of the Bruce treadmill protocol (work load equivalent to Bruce stage 3).

RESULTS

For each subject, regression of QTo (ms) versus heart rate (beats/min) resulted in a slope (reflecting the "dynamic" change in QTo during effort), an adjusted intercept (reflecting QTo extrapolated to a heart rate of 60 beats/min) and a significant correlation coefficient (r) value. Under these conditions, mean +/- SD (5th to 95th percentile) values for men were -1.45 +/- 0.34 ms/beat per min (-0.90, "less dynamic" to -1.96, "more dynamic") for the slope; 403 +/- 21 ms (365 to 431) for the adjusted intercept; and -0.93 +/- 0.06 (-0.81 to -0.99) for r. Values for women were more dynamic, with a mean slope of -1.74 +/- 0.32 ms/beat per min (-1.23 to -2.18, p < 0.0005 vs. men) and higher adjusted intercept of 426 +/- 23 ms (392 to 462, p < 0.0001 vs. men) at similar strength of correlation (r = -0.95 +/- 0.06). Corresponding normal data were also tabulated for QTm behavior and QT-RR interval behavior during exercise.

CONCLUSIONS

These data provide a "dynamic" definition of normal and abnormal repolarization and describe normal limits for the linear relations of the QTo and QTm intervals with respect to heart rate and cycle length during submaximal exercise in normal men and women.

Ventricular repolarization is correlated with metabolic control in newly diagnosed type 2 diabetes

Good metabolic control may improve cardiac function in diabetic patients. It is not known, however, whether this functional improvement is associated with concomitant electrocardiographic changes. The aim of the present prospective study was to evaluate the quantitative electrocardiographic and vectorcardiographic correlates of metabolic control, left ventricular function and dimensions, and autonomic nervous function in patients with newly diagnosed Type 2 diabetes. We studied 35 patients (20 men, 15 women; age 52 +/- 6 years (mean +/- SD) with normal electrocardiograms at 1.5 and 15 months after the diagnosis of Type 2 (non-insulin-dependent) diabetes. During the follow-up, body weight decreased, and significant improvement was observed in metabolic control, cardiac function and autonomic nervous function. Concomitantly, maximal spatial vector of T wave increased from 238 +/- 122 to 284 +/- 141 microV (P < 0.01), and this increase was correlated with a decrease in glycosylated haemoglobin A1C (r = -0.45, P < 0.01) and plasma insulin (r = -0.46, P < 0.01). In addition, duration of QRS complex shortened from 94 +/- 9 to 92 +/- 8 ms (P < 0.05), and this shortening was correlated with an increase in heart rate variability (r = -0.34; P < 0.05) and a decrease in peak early to late left ventricular filling flow velocity (r = 0.35, P < 0.05). These changes were most prominent in patients with co-existing hypertension and coronary artery disease. In conclusion, improving metabolic control of diabetes is associated with changes in ventricular repolarization and shortening of QRS complex duration.

Effect of oxybutynin on the QTc interval in elderly patients with urinary incontinence

1. Terodiline, an anticholinergic drug with calcium antagonist properties, is associated with QT prolongation and ventricular arrhythmias. It is not known if oxybutynin, a drug with a similar pharmacological profile, causes QT prolongation. ECGs were obtained before and at least 4 weeks after commencement of oxybutynin (mean daily dose 7.6, range 2.5-10 mg), in 21 elderly (mean age 75, range 58-88 years) patients treated for urinary incontinence. Heart rate, (mean +/- s.d.) 74 +/- 11 vs 69 +/- 11 beats min-1, -6 (-13,2), before vs during oxybutynin therapy, mean difference (95% confidence intervals); PR interval, 168 +/- 27 vs 156 +/- 27 ms, -11 (-26,3); QTc 454 +/- 27 vs 447 +/- 31 ms1/2, -9 (-23,5), and QTc dispersion, QTc max-QTc min, 68 +/- 24 vs 63 +/- 26 ms1/2, -1 (-15,14) were all unaltered by oxybutynin therapy. The lack of an effect on resting heart rate suggests that oxybutynin has little anticholinergic action at cardiac M2 receptors at usually administered doses. Oxybutynin therapy is not associated with QTc interval prolongation and is unlikely to produce ventricular arrhythmias.

Concentration dependent cardiotoxicity of terodiline in patients treated for urinary incontinence

OBJECTIVE

Terodiline, an antimuscarinic and calcium antagonist drug, was used to treat detrusor instability but was withdrawn in 1991 after provoking serious ventricular arrhythmias associated with increases in the corrected QT interval (QTc). This research was performed to relate drug induced electrocardiographic changes in asymptomatic recipients to plasma concentrations of the R(+) and S(-) terodiline enantiomers.

SETTING

Urological and geriatric clinics and wards.

SUBJECTS

Asymptomatic patients taking terodiline in stable dose.

METHODS

Electrocardiograms (50 mm/s) were collected from patients while they were taking terodiline and compared with ECGs obtained before or after terodiline. QT interval, heart rate corrected QT interval (QTc), and QT dispersion (QTd) were measured. Drug induced electrocardiographic changes were related to plasma concentrations of R(+) and S(-) terodiline.

RESULTS

During terodiline treatment mean QTc and QTd were prolonged (491(43) and 84 (35) ms 1/2) compared with measurements made off therapy (443 (33) and 42 (17) ms 1/2, paired t tests, P < 0.002 and P < 0.01 respectively) in the 12 patients in sinus rhythm. The mean (95% confidence interval) drug induced increases were 48 (23 to 74) ms 1/2 for QTc and 42 (13 to 70) ms 1/2 for QTd. These increases correlated with total plasma terodiline (QTc: r = 0.77, P < 0.006, QTd: r = 0.68, P < 0.025) and with plasma concentrations of both terodiline enantiomers.

CONCLUSIONS

Terodiline increases QTc and QTd in a concentration dependent manner. It is not clear whether this is a stereoselective effect and, if so, which enantiomer is responsible. The results suggest that drug induced torsade de pointes is a type A (concentration dependent) adverse drug reaction.

QTc interval prolongation during infusion with dipyridamole or adenosine

The aim of our study was to discover whether there was a relationship between the QTc interval prolongation on the standard 12-lead electrocardiogram (ECG) and provoked myocardial ischemia. Since the increase of adenosine plasma levels, obtained either with adenosine or dipyridamole (an adenosine reuptake inhibitor) infusion, has been used to test the coronary artery reserve in patients affected by coronary artery disease, the QTc interval modifications during dipyridamole or adenosine echocardiographic stress test were evaluated. Twenty-five patients admitted to our Institute for evaluation of chest pain of suspected myocardial origin underwent an echocardiographic dipyridamole stress test (0.84 mg/kg over 10 min) after discontinuation of antianginal treatment. Of these patients, 10 underwent an echocardiographic adenosine stress test (scalar doses of 50, 75, 100, 140 micrograms/kg/min) after 48-72 h. The Bazett formula was used to evaluate the QTc interval. After dipyridamole and adenosine administration, a significant prolongation of the QTc interval was observed only in those patients who had positive test results. Our data suggested that QTc interval prolongation during pharmacological stress tests might be considered a marker of myocardial ischemia.

QTc behavior during treadmill exercise as a function of the underlying QT-heart rate relationship

A mathematic description of the behavior of the Bazett-corrected QTc interval during exercise was developed from the underlying relationship between the unadjusted QT interval and heart rate in 94 normal men. Measurements were made from digitized precordial lead V5 complexes that were averaged by computer over 20-second periods at upright control (mean rate, 78 beats/min), during moderate exercise (mean rate, 125 beats/min), and at peak effort (mean rate, 162 beats/min), using a gently graded treadmill protocol that produces small heart rate increments between 2-minute stages. Although the group mean QTc interval increased during early exercise and decreased during higher exercise workloads, the mean unadjusted QT interval decreased throughout exercise in a strongly linear relationship with increasing heart rate: QT[ms] = 481 - 1.32HR, R2 = .99, where HR stands for heart rate. As a consequence of this linearity, the behavior of the QTc interval over a range of heart rates generally found during exercise could be modeled as a function of the slope (m) and intercept (b) of the observed relationship, since the Bazett relationship QTc = QT[ms]/R-R0.5 can, in this context, be rewritten simply as QTc = (481 - 1.32HR)/(60/HR)0.5, which reproduces the observed biphasic QTc interval behavior. Plots of the generalized equation QTc = (b - mHR)/(60/HR)0.5 allow theoretical exploration of QTc interval behavior that might result from varied disorders with different slopes (m) and intercepts (b), and these regression-based descriptors of the QT-heart rate relationship may provide useful, additional definitions of normal and abnormal QT interval behavior during exercise.

Rate-corrected QT interval: techniques and limitations

The duration of the QT interval on the surface electrocardiogram represents the time required for all ventricular depolarization and repolarization processes to occur. Among the many physiologic and pathologic factors that contribute to the QT interval, heart rate plays a major role. Several approaches have been used to correct the QT interval, all of which take into account the heart rate at which the interval is measured. The simplest and most common approach to correcting the QT interval is to divide its value by the square root of the preceding RR interval expressed in seconds, i.e., by using Bazett's formula. This calculation provides a corrected QT (QTc) interval that represents the QT interval normalized for a heart rate of 60 beats/min. However, several studies have shown that Bazett's correction formula is not optimal. Fridericia's cube-root formula has been shown to perform better in correcting the QT interval for heart rate. Other formulas require the measurement of several QT-RR pairs at various heart rates to obtain a reliable QTc interval and are therefore not easily usable. Any correction formula is likely to introduce an error in assessing the QTc interval. Although the importance of this error should not be minimized, the corrected QT interval remains useful in assessing the effects of drugs on the duration of repolarization. For this purpose, Fridericia's cube-root formula is preferable to Bazett's square-root formula.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic basis of the antiarrhythmic and hemodynamic effects of sotalol

Sotalol is a competitive beta adrenoceptor antagonist devoid of membrane-stabilizing activity and intrinsic sympathomimetic activity that has no preferential actions on beta 1 or beta 2 responses. No other tested receptor systems are affected by sotalol. In addition to having class II (beta blockade) effects, sotalol also has class III antiarrhythmic activity. It increases the action potential duration (APD) and prolongs atrial and ventricular repolarization. The effect on APD is independent of beta blockade; the same effect is seen with similar concentrations of the d stereoisomer of sotalol, which does not have beta-blocking activity. Sotalol prolongs the rate-corrected QT interval and ventricular and atrial refractoriness without affecting atrial, His-Purkinje, or ventricular conduction velocity. Atrioventricular nodal conduction is decreased, largely because of beta blockade. Sotalol increases the fibrillation threshold and decreases the defibrillation threshold. Sotalol is an effective antiarrhythmic in various animal models of arrhythmia (e.g., chloroform, hydrocarbon-catecholamine, ouabain, and coronary ligation). In addition, it reduces the severity and frequency of arrhythmias induced by programmed electrical simulation. By comparison, metoprolol is ineffective and d-sotalol is as effective as the racemate in this model, indicating that this effect is independent of beta blockade. Sotalol causes concentration-dependent increases in the contractility of isolated ventricular tissue that is not blocked by previous beta or alpha blockade or catecholamine depletion. The positive inotropic effect may be related to inhibition of time-dependent K+ current responsible for the increase in APD. Like propranolol, sotalol decreases contractile force, heart rate, arterial blood pressure, left ventricular dP/dt, and cardiac output in intact animals due to blockade of circulating catecholamines. Sotalol consistently reduces the heart rate to a greater degree than propranolol and causes significantly less cardiac suppression than propranolol at a given heart rate.

Optic disk cupping and electrocardiographic abnormalities in an American pedigree with Leber's hereditary optic neuropathy

We examined the clinical characteristics of affected and unaffected members of an American black family with the 11778 mitochondrial DNA mutation associated with Leber's hereditary optic neuropathy. Thirty-six individuals from four generations were included. All maternally related subjects were shown to be essentially homoplasmic for the 11778 mitochondrial DNA mutation in blood. Paternally related subjects did not carry this mutation. Patients affected with optic neuropathy had optic nerve head cupping. Loss of unmyelinated axons from the prelaminar optic nerve may be responsible for cupping in these patients. Electrocardiographic analysis of subjects carrying the 11778 mitochondrial DNA mutation disclosed statistically significant (P = .02) prolongation of the corrected OT interval as compared to control subjects. While the clinical significance of this magnitude of corrected QT prolongation is unknown, it may represent a systemic manifestation of the 11778 mutation. No electrocardiographic evidence of preexcitation syndromes was seen.

Pharmacology, pharmacodynamics and pharmacokinetics of sotalol

Sotalol is a nonselective, water-soluble beta-adrenoceptor antagonist with no membrane-stabilizing activity or intrinsic sympathomimetic activity. Sotalol is, essentially, completely absorbed and is not metabolized. Consequently, bioavailability is close to 100%. Age and food have slight but unimportant effects on bioavailability. Cmax of sotalol is 2 to 3 hours with a t1/2 between 7 and 15 hours. Excretion of sotalol is primarily through the kidneys, with no metabolism by liver and no first-pass effect. Therefore, sotalol plasma levels and half-life are directly related to creatinine clearance and glomerular filtration rate. Appropriate dose adjustments must be made for patients with impaired renal function or increased renal blood flow, as in pregnancy. The beta-adrenoceptor antagonistic effects of sotalol are directly related to plasma levels, which, in turn, are directly related to dose. However, the beta-adrenoceptor antagonism t1/2 is longer than the sotalol plasma t1/2. As a consequence of its ability to prolong the action potential duration, sotalol also increases cardiac contractility in isolated ventricular, but not atrial, preparations by 20 to 40%. This positive inotropic effect is not blocked by beta or alpha blockade or reserpine pretreatment and seems to be related to sotalol's effects on cardiac ionic currents. Like the effects of sotalol on action potential duration, the positive inotropic effects are inversely proportional to rate. The hemodynamics of sotalol indicate a relative lack of direct cardiac depressant activity in both animals and humans. The typical hemodynamic effects of sotalol in normotensive humans, even with depressed myocardial function, are a reduction in heart rate with little or no change in blood pressure, a reduction in cardiac output with no change in stroke volume, and little or no change in pulmonary wedge pressure and left ventricular end-diastolic pressure or volume, and little or no change in ejection fraction either at rest or during exercise.