Arrhythmogenic mechanisms of QT prolonging drugs: is QT prolongation really the problem?

The natural history of QTc interval and its clinical impact in coronavirus disease 2019 survivors after 1 year

Background and objective

Prolonged QTc interval on admission and a higher risk of death in SARS-CoV-2 patients have been reported. The long-term clinical impact of prolonged QTc interval is unknown. This study examined the relationship in COVID-19 survivors of a prolonged QTc on admission with long-term adverse events, changes in QTc duration and its impact on 1-year prognosis, and factors associated with a prolonged QTc at follow-up.

Methods

We conducted a single-center prospective cohort study of 523 SARS-CoV-2-positive patients who were alive on discharge. An electrocardiogram was taken on these patients within the first 48 h after diagnosis and before the administration of any medication with a known effect on QT interval and repeated in 421 patients 7 months after discharge. Mortality, hospital readmission, and new arrhythmia rates 1 year after discharge were reviewed.

Results

Thirty-one (6.3%) survivors had a baseline prolonged QTc. They were older, had more cardiovascular risk factors, cardiac disease, and comorbidities, and higher levels of terminal pro-brain natriuretic peptide. There was no relationship between prolonged QTc on admission and the 1-year endpoint (9.8% vs. 5.5%, p = 0.212). In 84% of survivors with prolonged baseline QTc, it normalized at 7.9 ± 2.2 months. Of the survivors, 2.4% had prolonged QTc at follow-up, and this was independently associated with obesity, ischemic cardiomyopathy, chronic obstructive pulmonary disease, and cancer. Prolonged baseline QTc was not independently associated with the composite adverse event at 1 year.

Conclusions

Prolonged QTc in the acute phase normalized in most COVID-19 survivors and had no clinical long-term impact. Prolonged QTc at follow-up was related to the presence of obesity and previously acquired chronic diseases and was not related to 1-year prognosis.

Levosimendan attenuates electrical alternans and prevents ventricular arrhythmia during therapeutic hypothermia in isolated rabbit hearts

BACKGROUND

Therapeutic hypothermia (TH) increases the susceptibility to ventricular arrhythmias (VAs) by prolonging action potential duration (APD) and facilitating arrhythmogenic spatially discordant alternans (SDA). Levosimendan, a calcium sensitizer, has been reported to shorten APD by enhancing the adenosine triphosphate (ATP)-sensitive K current.

OBJECTIVE

The purpose of this study was to test the hypothesis that, during TH, levosimendan shortens the already prolonged APD, attenuates SDA, and prevents VA.

METHODS

Langendorff-perfused isolated rabbit hearts were subjected to TH (30°C) for 15 minutes, followed by treatment with either levosimendan 0.5 μM (n = 9) or vehicle (n = 8) for an additional 30 minutes under TH. Using an optical mapping system, epicardial APD was evaluated by S1 pacing. SDA threshold was defined as the longest pacing cycle length (PCL) that induces the phenomenon of SDA. Ventricular fibrillation (VF) inducibility was evaluated by burst pacing for 30 seconds at the shortest PCL that achieved 1:1 ventricular capture.

RESULTS

During TH, levosimendan shortened ventricular APD (PCL 400 ms; from 259 ± 8 ms to 241 ± 18 ms; P = .036) and decreased SDA threshold (from 327 ± 88 ms to 311 ± 68 ms; P = .011). VF inducibility was lowered from 39% ± 30% to 14% ± 12% with levosimendan (P = .018), whereas APD at PCL 400 ms (P = .161), SDA threshold (P = 1), and VF inducibility (P = .173) were not changed by vehicle.

CONCLUSION

During TH, levosimendan could protect hearts against VA by shortening APD and decreasing SDA threshold. Enhancing ATP-sensitive K current with levosimendan might be a novel approach to preventing VA during TH.

A deep learning platform to assess drug proarrhythmia risk

Drug safety initiatives have endorsed human iPSC-derived cardiomyocytes (hiPSC-CMs) as an in vitro model for predicting drug-induced cardiac arrhythmia. However, the extent to which human-defined features of in vitro arrhythmia predict actual clinical risk has been much debated. Here, we trained a convolutional neural network classifier (CNN) to learn features of in vitro action potential recordings of hiPSC-CMs that are associated with lethal Torsade de Pointes arrhythmia. The CNN classifier accurately predicted the risk of drug-induced arrhythmia in people. The risk profile of the test drugs was similar across hiPSC-CMs derived from different healthy donors. In contrast, pathogenic mutations that cause arrhythmogenic cardiomyopathies in patients significantly increased the proarrhythmic propensity to certain intermediate and high-risk drugs in the hiPSC-CMs. Thus, deep learning can identify in vitro arrhythmic features that correlate with clinical arrhythmia and discern the influence of patient genetics on the risk of drug-induced arrhythmia.

Anaesthetists’ Knowledge of the QT Interval in a Teaching Hospital

Many drugs used in anaesthesia may prolong the QT interval of the electrocardiogram (ECG), and recent U.S. Food and Drug Administration guidelines mandate monitoring of the ECG before, during and after droperidol administration. We surveyed 41 trainee and consultant anaesthetists in our Department to determine current practice and knowledge of the QT interval to investigate if this is a practical proposition. A response rate of 98% (40/41) was obtained. The majority of respondents expressed moderate to high levels of confidence in interpreting the ECG, and this was related to years of training (rho 0.36, P=0.024). A total of 27 respondents (65%) were able to correctly identify the QT interval on a schematic representation of the ECG, trainees 70% vs consultants 60%, P=0.51. When asked to name drugs that altered the QT interval, droperidol was included by 11 of the 40 respondents (28%); trainees 10% vs consultants 45%, OR 7.4 (95% CI: 1.3–41), P=0.013. Torsades de Pointes was correctly identified as a possible consequence of a prolonged QT interval by 65% of trainees and 70% of consultants, P=0.83. The results suggest that QT interval measurement is not widely practised by anaesthetists, although its clinical significance is well known, and interpretation would be unreliable without further education.

QTc interval prolongation in critically ill patients: Prevalence, risk factors and associated medications

PURPOSE

To investigate the prevalence and risk factors of acquired long QT syndrome (LQTS) on admission to a general Intensive Care Unit (ICU), and to assess the risk of LQTS associated with prescribed medications.

METHODS

Prospective observational, cross-sectional study approved by the Institutional Review Board. Between May 2014 and July 2016, 412 patients >18 years-old consecutively admitted to the ICU of a university hospital were included. LQTS was defined as a QT interval on the admission electrocardiogram corrected using Bazett's formula (QTc) >460 ms for men and >470 ms for women. All medications administered within 24 hours before admission were recorded. Logistic regression was used.

RESULTS

LQTS prevalence was 27.9%. In LQTS patients, 70.4% had ≥ 1 LQTS-inducing drug prescribed in the 24 hours prior to ICU admission versus 70.4% in non-LQTS patients (p = 0.99). Bradycardia and Charlson morbidity index score are independent risk factors for LQTS. Haloperidol (OR 4.416), amiodarone (OR 2.509) and furosemide (OR 1.895) were associated with LQTS, as well as another drug not yet described, namely clopidogrel (OR 2.241).

CONCLUSIONS

The LQTS is highly prevalent in critically ill patients, ICU patients are often admitted with LQTS-inducing medications, and patients with slow heart rate or with high Charlson comorbidity index should be evaluated for LQTS.

The effect of sevoflurane on the transmural dispersion of repolarisation in patients with type 2 diabetes mellitus: a prospective observational study

The 'torsadogenic' property of a drug is linked to its ability to increase the transmural dispersion of repolarisation, represented by the interval between the peak of, and the end of, the T-wave (Tp-e interval) in an electrocardiogram. Reports have consistently shown that sevoflurane does not increase the Tp-e interval. Type 2 diabetes is a risk factor for increased QTc (rate-corrected QT interval), QTcd (rate-corrected QTc dispersion: difference between the maximum and the minimum QTc interval), and Tp-e, as well as the rate-corrected Tp-e (Tp-e/QTc ratio). The study aimed to ascertain whether sevoflurane increased the Tp-e interval and Tp-e/QTc ratio in patients with diabetes, thereby increasing their risk of torsades. We enrolled 35 female patients; 17 with type 2 diabetes and 18 controls undergoing non-laparoscopic surgery under sevoflurane anaesthesia. The Tp-e interval, Tp-e/QTc ratio, QTc and QTcd were recorded after intubation, 5, 10, 30 and 60 minutes into the anaesthetic, and were compared between the groups. No significant increase in the Tp-e interval or Tp-e/QTc was observed between or within the groups (a 13 ms increase was considered significant). In the control group, the QTc was significantly increased from baseline immediately after intubation (449 versus 414 ms, <i>P</i> <0.001); at 5 minutes (434 versus 414 ms, <i>P</i>=0.01); at 10 minutes (444 versus 414 ms, <i>P</i>=0.002); at 30 minutes (439 versus 414 ms, <i>P</i>=0.001) and at 60 minutes (442 versus 414 ms; <i>P</i> <0.001) (a 20 ms increase was considered significant). No significant increase in QTc was observed in the diabetic group. There were no between or within group differences observed for QTcd. Our findings suggest that sevoflurane does not have a significant predictable pro-arrhythmic effect in type 2 diabetic patients in the absence of other factors affecting ventricular repolarisation.

Influence of long-term oral application of quinolones on the ECG curve in dogs

The aim of the study was to analyse the influence of enrofloxacin and pradofloxacin administered orally for 14 days on the ECG in dogs. The ECG was performed before and after a 14 day period of quinolone administration. There was an increase in the QTc and the TpTe interval in the group treated with quinolones. QTc was prolonged by 24 ms (p=0.001). The TpTe interval was shortened, on average, by 6.55 ms (p=0.048). In the group treated with enrofloxacin, QTc was prolonged by 16.27 ms (p=0.006) and the TpTe interval was shortened by 9.64 ms (p=0.050), the TpTe/QT index was reduced by 0.034 (p=0.050) on average. In dogs treated with pradofloxacin, QTc was prolonged by 21.55 ms (p=0.012) on average. The results suggest that a prolonged administration of quinolones can increase the risk of arrhythmias. Furthermore, different generations of these drugs increase this risk to various degrees. The study proved that second generation quinolones, such as enrofloxacin, significantly change the phase of depolarization and repolarization of the ventricles, at the same time increasing the risk of ventricular arrythmia. Pradofloxacin does not change the TpTe and TpTe/QT values, so it is safer in use.

QT Prolongation and Malignant Arrhythmia: How Serious a Problem?

QT prolongation constitutes one of the most frequently encountered electrical disorders of the myocardium. This is due not only to the presence of several associated congenital syndrome but also, and mainly, due to the QT-prolonging effects of several acquired conditions, such as ischaemia and heart failure, as well as multiple medications from widely different categories. Propensity of repolarization disturbances to arrhythmia appears to be inherent in the function of and electrophysiology of the myocardium. In the present review the issue of QT prolongation will be addressed in terms of pathophysiology, arrhythmogenesis, treatment and risk stratification approaches. Although already discussed in literature, it is hoped that the mechanistic approach of the present review will assist in improved understanding of the underlying changes in electrophysiology, as well as the rationale for current diagnostic and therapeutic approaches.

Biophysics and Molecular Biology of Cardiac Ion Channels for the Safety Pharmacologist

Cardiac safety pharmacology is a continuously evolving discipline that uses the basic principles of pharmacology in a regulatory-driven process to generate data to inform risk/benefit assessment of a new chemical entity (NCE). The aim of cardiac safety pharmacology is to characterise the pharmacodynamic/pharmacokinetic (PK/PD) relationship of a drug's adverse effects on the heart using continuously evolving methodology. Unlike Toxicology, safety pharmacology includes within its remit a regulatory requirement to predict the risk of rare cardiotoxic (potentially lethal) events such as torsades de pointes (TdP), which is statistically associated with drug-induced changes in the QT interval of the ECG due to blockade of I Kr or K v11.1 current encoded by hERG. This gives safety pharmacology its unique character. The key issues for the safety pharmacology assessment of a drug on the heart are detection of an adverse effect liability, projection of the data into safety margin calculation and clinical safety monitoring. This chapter will briefly review the current cardiac safety pharmacology paradigm outlined in the ICH S7A and ICH S7B guidance documents and the non-clinical models and methods used in the evaluation of new chemical entities in order to define the integrated risk assessment for submission to regulatory authorities. An overview of how the present cardiac paradigm was developed will be discussed, explaining how it was based upon marketing authorisation withdrawal of many non-cardiovascular compounds due to unanticipated proarrhythmic effects. The role of related biomarkers (of cardiac repolarisation, e.g. prolongation of the QT interval of the ECG) will be considered. We will also provide an overview of the 'non-hERG-centric' concepts utilised in the evolving comprehensive in vitro proarrhythmia assay (CIPA) that details conduct of the proposed ion channel battery test, use of human stem cells and application of in silico models to early cardiac safety assessment. The summary of our current understanding of the triggers of TdP will include the interplay between action potential (AP) prolongation, early and delayed afterdepolarisation and substrates for re-entry arrhythmias.

Effect of dexmedetomidine on the corrected QT and Tp-e intervals during spinal anesthesia

PURPOSE

The aim of this study is to evaluate the effect of dexmedetomidine on corrected QT (QTc) and Tp-e intervals in patients undergoing spinal anesthesia.

MATERIALS AND METHODS

We studied 50 patients who were scheduled to undergo spinal anesthesia before orthopedic surgeries. Patients were allocated to receive either an infusion of dexmedetomidine or normal saline after spinal anesthesia.

RESULTS

QTc intervals were significantly prolonged after spinal anesthesia, and the prolonged QTc interval returned to baseline values 10 minutes after either normal saline or dexmedetomidine administration in both groups. The QTc interval values after dexmedetomidine administration were significantly shorter compared to the QTc interval values just before dexmedetomidine administration.

CONCLUSION

Dexmedetomidine could promote the return of a prolonged QTc interval induced by spinal anesthesia and might be helpful in patients who have a prolonged QTc interval.

Intravenous palonosetron increases the incidence of QTc prolongation during sevoflurane general anesthesia for laparotomy

Background

Palonosetron is a recently introduced 5-hydroxytryptamine-3 (5-HT₃) receptor antagonist useful for postoperative nausea and vomiting prophylaxis. However, 5-HT₃ receptor antagonists increase the corrected QT (QTc) interval in patients who undergo general anesthesia. This retrospective study was performed to evaluate whether palonosetron would induce a QTc prolongation in patients undergoing general anesthesia with sevoflurane.

Methods

We reviewed a database of 81 patients who underwent general anesthesia with sevoflurane. We divided the records into palonosetron (n = 41) and control (n = 40) groups according to the use of intraoperative palonosetron, and analyzed the electrocardiographic data before anesthesia and 30, 60, 90, and 120 min after skin incision. Changes in the QTc interval from baseline, mean blood pressure, heart rate, body temperature, and sevoflurane concentrations at each time point were compared between the two groups.

Results

The QTc intervals at skin incision, and 30, 60, 90, and 120 min after the skin incision during general anesthesia were significantly longer than those at baseline in the two groups (P < 0.001). The changes in the QTc intervals were not different between the two groups (P = 0.41). However, six patients in the palonosetron group showed a QTc interval > 500 ms 30 min after skin incision, whereas no patient did in the control group (P = 0.01). No significant differences were observed between the two groups in mean blood pressure, body temperature, heart rate, or sevoflurane concentrations.

Conclusions

Palonosetron may induce QTc prolongation during the early general anesthesia period with sevoflurane.

Acquired long QT syndrome: frequency, onset, and risk factors in intensive care patients

BACKGROUND

Acquired long QT syndrome is a reversible condition that can lead to torsades de pointes and sudden cardiac death.

OBJECTIVE

To determine the frequency, onset, frequency of medications, and risk factors for the syndrome in intensive care patients.

METHODS

In a retrospective chart review of 88 subjects, hourly corrected QT intervals calculated by using the Bazett formula were collected. Acquired long QT syndrome was defined as a corrected QT of 500 milliseconds or longer or an increase in corrected QT of 60 milliseconds or greater from baseline level. Risk factors and medications administered were collected from patients' medical records.

RESULTS

The syndrome occurred in 46 patients (52%); mean time of onset was 7.4 hours (SD, 9.4) from time of admission. Among the 88 patients, 52 (59%) received a known QTc-prolonging medication. Among the 46 with the syndrome, 23 (50%) received a known QT-prolonging medication. No other risk factor studied was significantly predictive of the syndrome.

CONCLUSIONS

Acquired long QT syndrome occurs in patients not treated with a known QT-prolonging medication, indicating the importance of frequent QT monitoring of all intensive care patients.

QT interval abnormalities: risk factors and perioperative management in long QT syndromes and Torsades de Pointes

Electrophysiological abnormalities of the QT interval of the standard electrocardiogram are not uncommon. Congenital long QT syndrome is due to mutations of several possible genes (genotype) that result in prolongation of the corrected QT interval (phenotype). Abnormalities of the QT interval can be acquired and are often drug-induced. Torsades de Pointes (TP) is an arrhythmia that is a result of aberrant repolarization/QT abnormalities. If not recognized and corrected quickly, QT interval abnormalities may precipitate potentially fatal ventricular dysrhythmias. The main mechanism responsible for the development of QT prolongation is blockade of the rapid component of the delayed rectifier potassium current (I kr), encoded for by the human-ether-a-go-go-related gene (hERG). The objectives of this review were (1) to describe the electrical pathophysiology of QT interval abnormalities, (2) to differentiate congenital from acquired QT interval abnormalities, (3) to describe the currently known risk factors for QT interval abnormalities, (4) to identify current drug-induced causes of acquired QT interval abnormalities, and (5) to recommend immediate and effective management strategies to prevent unanticipated dysrhythmias and deaths from QT abnormalities in the perioperative period.

Induced pluripotent stem cells in cardiovascular drug discovery

The unexpected discovery that somatic cells can be reprogrammed to a pluripotent state yielding induced pluripotent stem cells has made it possible to produce cardiovascular cells exhibiting inherited traits and disorders. Use of these cells in high throughput analyses should broaden our insight into fundamental disease mechanisms and provide many benefits for patients, including new therapeutics and individually tailored therapies. Here we review recent progress in generating induced pluripotent stem cell-based models of cardiovascular disease and their multiple applications in drug development.

Carvedilol analogue inhibits triggered activities evoked by both early and delayed afterdepolarizations

BACKGROUND

Carvedilol and its analogues suppress delayed afterdepolarizations (DADs) and catecholaminergic polymorphic ventricular tachycardias by direct action on the cardiac ryanodine receptor type 2 (RyR2).

OBJECTIVE

To test a hypothesis that carvedilol analogue may also prevent triggered activities (TAs) through the suppression of early afterdepolarizations (EADs).

METHODS

Intracellular Ca(2+) and membrane voltage were simultaneously recorded by using optical mapping technique in Langendorff-perfused mouse and rabbit hearts to study the effect of carvedilol analogue VK-II-36, which does not have significant beta-blocking effects.

RESULTS

Spontaneous intracellular Ca(2+) elevations (SCaEs) during diastole were induced by rapid ventricular pacing and isoproterenol infusion in intact rabbit ventricles. Systolic and diastolic SCaEs were simultaneously noted in Langendorff-perfused RyR2 R4496(+/-) mouse hearts after creating atrioventricular block. VK-II-36 effectively suppressed SCaEs and eliminated TAs observed in both mouse and rabbit ventricles. We tested the effect of VK-II-36 on EADs by using a rabbit model of acquired long QT syndrome, in which phase 2 and phase 3 EADs were observed in association with systolic SCaEs. VK-II-36 abolished the systolic SCaEs and phase 2 EADs, and greatly decreased the dispersion of repolarization and the amplitude of phase 3 EADs. VK-II-36 completely prevented EAD-mediated TAs in all ventricles studied.

CONCLUSIONS

A carvedilol analogue, VK-II-36, inhibits ventricular tachyarrhythmias in intact mouse and rabbit ventricles by the suppression of SCaEs, independent of beta-blocking activity. The RyR2 may be a potential target for treating focal ventricular arrhythmias triggered by either EADs or DADs.

High throughput measurement of Ca²⁺ dynamics for drug risk assessment in human stem cell-derived cardiomyocytes by kinetic image cytometry

Current methods to measure physiological properties of cardiomyocytes and predict fatal arrhythmias that can cause sudden death, such as Torsade de Pointes, lack either the automation and throughput needed for early-stage drug discovery and/or have poor predictive value. To increase throughput and predictive power of in vitro assays, we developed kinetic imaging cytometry (KIC) for automated cell-by-cell analyses via intracellular fluorescence Ca²⁺ indicators. The KIC instrument simultaneously records and analyzes intracellular calcium concentration [Ca²⁺](i) at 30-ms resolution from hundreds of individual cells/well of 96-well plates in seconds, providing kinetic details not previously possible with well averaging technologies such as plate readers. Analyses of human embryonic stem cell and induced pluripotent stem cell-derived cardiomyocytes revealed effects of known cardiotoxic and arrhythmogenic drugs on kinetic parameters of Ca²⁺ dynamics, suggesting that KIC will aid in the assessment of cardiotoxic risk and in the elucidation of pathogenic mechanisms of heart disease associated with drugs treatment and/or genetic background.

Modulation of the late sodium current by ATX-II and ranolazine affects the reverse use-dependence and proarrhythmic liability of IKr blockade

BACKGROUND AND PURPOSE

Drug-induced torsades de pointes (TdP) often occurs during bradycardia due to reverse use-dependence. We tested the hypothesis that inhibition or enhancement of late sodium current (I(Na,L) ) could modulate the drug-induced reverse use-dependence in QT and T(p-e) (an index of dispersion of repolarization), and therefore the liability for TdP.

EXPERIMENTAL APPROACH

Arterially perfused rabbit left ventricular wedge preparations were used. Action potentials from the endocardium were recorded simultaneously with a transmural ECG. The effects of Anemonia sulcata toxin (ATX-II) (an I(Na,L) enhancer), d,l-sotalol, clarithromycin and ranolazine (an I(Na,L) blocker) on rate-dependent changes in QT, T(p-e) and proarrhythmic events were tested, either alone or in combination. Rate-dependent QT and T(p-e) slopes and TdP score (a combined index of TdP liability) were calculated at control and during drug infusion.

KEY RESULTS

ATX-II (30 nM) and sotalol (300 µM) caused a marked increase in QT and T(p-e) intervals, steeper QT-basic cycle length (BCL) and T(p-e) -BCL slopes (i.e. reverse use-dependence), and TdP. Addition of ranolazine (15 µM) to ATX-II or sotalol significantly attenuated QT-BCL, T(p-e) -BCL slopes and the increased TdP scores. In contrast, clarithromycin (100 µM) moderately prolonged QT and T(p-e) without causing R-on-T extrasystole or TdP, but addition of ATX-II (1 nM) to clarithromycin markedly amplified the QT-BCL and T(p-e) -BCL slopes and further increased TdP score.

CONCLUSION AND IMPLICATIONS

Modulation of I(Na,L) altered drug-induced reverse use-dependence related to QT as well as T(p-e) , indicating that inhibition of I(Na,L) can markedly reduce the TdP liability of agents that prolong QT intervals.

Diastolic electromechanical coupling: association of the ECG T-peak to T-end interval with echocardiographic markers of diastolic dysfunction

BACKGROUND

Electromechanical coupling, a well-described phenomenon in systolic dysfunction, has not been well studied in diastole. We hypothesized that the ECG T-peak to T-end (TpTe) interval, representing transmural dispersion of repolarization, is associated with echocardiographic markers of diastolic dysfunction (DD).

METHODS AND RESULTS

We performed a prospective, cross-sectional study of the association between TpTe and markers of DD in 84 consecutive, unselected patients referred for exercise echocardiography. We systematically measured TpTe on the resting ECG, and we performed comprehensive assessment of DD at rest and at peak stress. ECGs and echocardiograms were analyzed independently, blinded to each other and to all clinical data. By univariable analysis, increased TpTe was associated with older age, increased E/e' ratio, and DD (P<0.05 for all associations after correcting for multiple comparisons). Increased TpTe was inversely associated with reduced tissue Doppler e' velocity, a marker of DD (R=-0.66, P<0.0001). This association persisted after adjusting for age, QTc, exercise-induced wall motion abnormalities, and left ventricular mass index (β=-0.41 [95% confidence interval, -0.70 to -0.12] cm/s per 10-ms increase in TpTe; P=0.006). Baseline TpTe was also independently associated with resting DD (adjusted odds ratio, 3.9 [95% confidence interval, 1.4-10.7]; P=0.009) and peak exercise E/e' ratio (P<0.0001).

CONCLUSIONS

Increased TpTe is associated with both resting and exercise-induced DD. Electromechanical coupling may represent a pathophysiologic link between electrical transmural dispersion of repolarization and abnormal myocardial relaxation, and may be a novel therapeutic target.

Drug-Induced QTc-Interval Prolongation in the Intensive Care Unit: Incidence and Predictors

There is a paucity of information regarding QTc prolongation in critically ill patients. A prospective observational study was conducted to assess the incidence and predictors of QTc prolongation associated with medications in intensive care unit (ICU) patients. Consecutive adult patients prescribed prespecified QTc-prolonging medications were assessed for development of the combined incidence of QTc >500 ms at anytime and QTc increase >60 ms above baseline. Over 3 months, 200 consecutive patients (63 ± 18 years; 52% female; 73% Caucasian; baseline QTc 447.3 ± 51.5 ms) were evaluated. The primary end point occurred in 48% of the patients (QTc >500 ms 40%, QTc increase >60 ms 29%). The majority of patients experienced a QTc >470 or 450 ms (60.5%). Mean increase in QTc at 48 hours was 20 ± 35 ms. Upon multivariate analysis, length of stay [odds ratio 1.30, 95% confidence interval (1.15, 1.47)] and baseline QTc [1.01 (1.01, 1.02)] were associated with an increased risk for the primary end point, while beta-blockers [0.41 (0.20, 0.81)] were associated with a risk reduction. In conclusion, increased risk of proarrhythmia, as assessed by QTc prolongation, occurs in the majority of ICU patients when prescribed medications with electrophysiologic properties. Increased vigilance is warranted. The possible protective effect of beta-blockers requires confirmation.

The isolated rabbit heart and Purkinje fibers as models for identifying proarrhythmic liability

INTRODUCTION

Delayed ventricular repolarization is associated with rare, but often fatal, polymorphic tachyarrhythmias named Torsades de Pointes. ICH S7B guideline recommends an integrated approach for cardiovascular preclinical evaluation of new drug candidates, including action potential assays (as a Purkinje fiber test) but also proarrhythmia models. The aim of this preliminary study was to compare the respective value of two preclinical in vitro rabbit cardiac preparations-the Purkinje fiber and the isolated perfused heart (Langendorff method)-based on effects of dofetilide, a selective IKr inhibitor.

METHODS

Transmembrane action potentials from rabbit Purkinje fibers were recorded using a conventional intracellular glass microelectrode. Electrocardiograms from rabbit isolated hearts were evaluated for QRS, QT and T wave durations (Tpeak-Tend). The pacing protocol was the same for both preparations (basal rate of 80 bpm and pacing of 40, 60 and 140 bpm). Dofetilide was tested in both systems at concentrations of 1, 3 and 10 nmol/L.

RESULTS

In Purkinje fibers dofetilide induced a concentration- and reverse use-dependent increase in action potential durations measured at 50 and 90% of repolarization. At 10 nmol/L, only 3/10 fibers showed early after depolarizations. In the isolated heart model, dofetilide also induced a similar concentration- and reverse use-dependent increase in QT-interval. From 3 nmol/L, major changes in T wave morphology, R-on-T extrasystoles and TdP were observed, mainly at low rate. Prior to arrhythmias, T wave shape and duration were markedly altered suggesting an increase in the heterogeneity of cardiac ventricular repolarization.

CONCLUSIONS

The effects of dofetilide were comparable in the two models for delayed repolarization but the isolated heart appears to be a better predictor for arrhythmias and a unique in vitro model to assess arrhythmogenic potential of QT prolonging compounds at least when associated with IKr/hERG inhibition.

hERG-related drug toxicity and models for predicting hERG liability and QT prolongation

BACKGROUND

hERG K(+) channels have been recognized as a primary antitarget in safety pharmacology. Their blockade, caused by several drugs with different therapeutic indications, may lead to QT prolongation and, eventually, to potentially fatal arrhythmia, namely torsade de pointes. Therefore, a number of preclinical models have been developed to predict hERG liability early in the drug development process.

OBJECTIVE

The aim of this review is to outline the present state of the art on drug-induced hERG blockade, providing insights on the predictive value of in vitro and in silico models for hERG liability.

METHODS

On the basis of latest reports, high-throughput preclinical models have been discussed outlining advantages and limitations.

CONCLUSION

Although no single model has an absolute value, an integrated risk assessment is recommended to predict the pro-arrhythmic risk of a given drug. This prediction requires expertise from different areas and should encompass emerging issues such as interference with hERG trafficking and QT shortening.

A study on electrocardiographic changes secondary to the use of tricyclic antidepressants in patients with chronic pain

BACKGROUND AND OBJECTIVES

Tricyclic antidepressants (TCAs) are widely used as analgesics in chronic lumbar pain and neuropathic pain. The objective of this study was to evaluate the electrocardiographic changes in patients with chronic pain treated with amitriptyline or imipramine.

METHODS

Forty patients, ages 26 to 81 years (57.27 +/- 13.65 years) of both genders (female 19, male 21), with neuropathic syndromes (lumbosciatalgia, postlaminectomy syndromes, and postherpetic neuritis, among others) participated in this study; 60% had cardiovascular diseases; 30% had changes in the ECG (RBBB, LBBB, first-degree AVB, LAHB, or PVCs). Three ECGs were done in each patient: one ECG was done before beginning treatment, and 30 and 60 days after beginning treatment evaluating PR, QRS, QT QTc, DQT DQTc, and HR. Thirty-two patients were on amitriptyline and eight on imipramine. The mean dose at the end of the study was 54.29 mg of amitriptyline and 46.87 mg of imipramine.

RESULTS

Analysis of electrocardiographic parameters after the use of TCAs showed that amitriptyline caused a transitory increase in heart rate in females (p = 0.049), and the duration of the QRS in patients 60 years or older and patients with cardiopathies (p = 0.01). In patients who received 75 mg of amitriptyline, the QTc interval was greater when compared to that of patients who received 25 mg of the drug (p = 0.0044). The increase in those parameters demonstrated the effects of amitriptyline on cardiac conduction; however, clinical compromise was not seen, since they remained within normal limits (QRS < 110 msec and QTc < 470 msec).

CONCLUSIONS

The chronic use of TACs proved to be safe and effective, and it did not show changes in cardiac conduction with clinical repercussion.

Slow delayed rectifier K+ current block by HMR 1556 increases dispersion of repolarization and promotes Torsades de Pointes in rabbit ventricles

BACKGROUND AND PURPOSE

The slow delayed rectifier K(+) current (I(Ks)) contributes to ventricular repolarization when the action potential (AP) is prolonged. I(Ks) block during drug-induced AP prolongation may promote Torsades de Pointes (TdP), but whether this is due to additional AP prolongation is uncertain.

EXPERIMENTAL APPROACH

In bradycardic perfused rabbit ventricles, the incidence of spontaneous TdP, monophasic AP duration at 90% repolarization (MAPD(90)) and ECG interval between the peak and the end of T wave (T(peak-end)) (index of dispersion of repolarization) were measured after the administration of veratridine (125 nM, slows Na(+) channel inactivation), dofetilide (7.5 or 10 nM, a rapid delayed rectifier blocker) and HMR 1556 (HMR, 100 nM, an I(Ks) blocker), alone or in combinations (n=6 each).

KEY RESULTS

HMR did not prolong MAPD(90), whereas veratridine or 7.5 nM dofetilide prolonged MAPD(90) (P<0.01) without inducing TdP. Veratridine+7.5 nM dofetilide additively prolonged MAPD(90) (P<0.05), induced 4+/-6 TdP per heart and prolonged T(peak-end) by 12+/-10 ms. Subsequent addition of HMR did not further prolonged MAPD(90), but increased the number of TdP to 22+/-18 per heart and increased T(peak-end) by 39+/-21 ms (P<0.05). Increasing dofetilide concentration from 7.5 to 10 nM (added to veratridine) produced a longer MAPD(90), but fewer TdP (5+/-5 per heart) and less T(peak-end) prolongation (17+/-8 ms) compared to the veratridine+7.5 nM dofetilide+HMR group (P<0.05).

CONCLUSIONS AND IMPLICATIONS

Adding I(Ks) block markedly increases TdP incidence in hearts predisposed to TdP development by increasing the dispersion of repolarization, but without additional AP prolongation.

T(p-e)/QT ratio as an index of arrhythmogenesis

An increasing number of basic and clinical studies have suggested that the interval from the peak to the end of the electrocardiographic T wave (T(p-e)) may correspond to the transmural dispersion of repolarization and that amplification of the T(p-e) interval is associated with malignant ventricular arrhythmias. In this review, we outline the utility of the T(p-e) interval and the T(p-e)/QT ratio as an electrocardiographic index of arrhythmogenesis for both congenital and acquired ion channel disease leading to ventricular arrhythmias. In healthy individuals, the T(p-e)/QT ratio has a mean value of approximately 0.21 in the precordial leads and it remains relatively constant between the heart rates from 60 to 100 beats per minute. Interestingly, the T(p-e)/QT ratio is significantly greater in the patients at risk for arrhythmic event such as those with long QT syndrome, Brugada syndrome, short QT syndrome, and also in patients with organic heart disease such as acute myocardial infarction. Functional reentry is the underlying mechanism for arrhythmogenesis associated with an increased T(p-e)/QT ratio.

Key clinical considerations for demonstrating the utility of preclinical models to predict clinical drug-induced torsades de pointes

While the QT/QTc interval is currently the best available clinical surrogate for the development of drug-induced torsades de pointes, it is overall an imperfect biomarker. In addition to low specificity for predicting arrhythmias, other issues relevant to using QT as a biomarker include (1) an apparent dissociation, for some drugs (for example, amiodarone, sodium pentobarbital, ranolazine) between QT/QTc interval prolongation and TdP risk, (2) Lack of clarity regarding what determines the relationship between QTc prolongation and TdP risk for an individual drug, (3) QT measurement issues, including effects of heart rate and autonomic perturbations, (4) the significant circadian changes to the QT/QTc interval and (5) concerns that the development, regulatory and commercial implications of finding even a mild QT prolongation effect during clinical development has significant impact the pharmaceutical discovery pipeline. These issues would be significantly reduced, clinical development simplified and marketing approval for some drugs might be accelerated if there were a battery of preclinical tests that could reliably predict a drug's propensity to cause TdP in humans, even in the presence of QTc interval prolongation. This approach is challenging and for it to be acceptable to pharmaceutical developers, the scientific community and regulators, it would need to be scientifically well validated. A very high-negative predictive value demonstrated in a wide range of drugs with different ionic effects would be critical. This manuscript explores the issues surrounding the use of QT as a clinical biomarker and potential approaches for validating preclinical assays for this purpose against clinical data sets.

Persistent atrial fibrillation is associated with reduced risk of torsades de pointes in patients with drug-induced long QT syndrome

OBJECTIVES

The goal of this study was to identify markers of torsades de pointes (TdP) in patients with drug-associated long QT syndrome (LQTS).

BACKGROUND

Drug-induced LQTS includes individuals developing marked prolongation of ventricular repolarization on exposure to an offending drug. Under these conditions, TdP develops in some but not all patients.

METHODS

This was a case-control study of 123 adults with drug-associated LQTS. Patients were divided into LQTS only (LQTS; n = 40, QT >500 ms on drug) and LQTS + TdP (TdP; n = 83).

RESULTS

Baseline QT intervals were similar in the 2 groups (381 +/- 38 ms [LQTS] vs. 388 +/- 43 ms [TdP]). Clinical variables associated with risk of TdP included hypokalemia and female gender; by contrast, persistent atrial fibrillation (AF) at the time of drug discontinuation for QT prolongation was protective despite similar heart rates in AF and sinus rhythm (n = 20, 71 +/- 13 beats/min vs. 69 +/- 13 beats/min). Electrocardiographic variables that significantly increased the risk for TdP included absolute and rate-corrected QT intervals (QTc) on drug therapy, the magnitude of QT and QTc interval prolongation, and the change in T(peak) to T(end) (DeltaT(p)-T(e)), a relatively new index of transmural dispersion of repolarization and potential arrhythmogenicity. Multivariable logistic regression analysis revealed that only gender was predictive for TdP, whereas persistent AF at the time of drug discontinuation for QT prolongation (odds ratio 0.14, 95% confidence interval 0.03 to 0.63, p = 0.01) was negatively associated with the arrhythmia.

CONCLUSIONS

This study strongly suggests that despite ongoing rate irregularity, AF reduces the likelihood of developing TdP after the administration of drugs that prolong cardiac repolarization.

Impact of study design on proarrhythmia prediction in the SCREENIT rabbit isolated heart model

INTRODUCTION

Prediction of the propensity of a compound to induce Torsades de Pointes continues to be a formidable challenge to the pharmaceutical industry. Development of an in vitro model for assessment of proarrhythmic potential offers the advantage of higher throughput and reduced compound quantity requirements when compared to in vivo studies. A rabbit isolated heart model (SCREENIT) has been reported to identify compounds with proarrhythmic potential based on the observance of compound-induced triangulation and instability of the monophasic action potential (MAP), ectopic beats, and reverse-use dependence of prolongation of the MAP duration. Previous reports have indicated that this model qualitatively identifies proarrhythmic compounds and suggest the use of this model to assign safety margins for human clinical use. The intent of this series of studies was to evaluate the impact of study design on the proarrhythmic concentration predicted by this model.

METHODS

Nine compounds of varying proarrhythmic potential and a negative control were tested in a blinded fashion using a series of different experimental protocols: Compounds were tested at multiple concentration ranges and extended perfusion times were also evaluated.

RESULTS

In general when the dataset is viewed as a whole, the model did identify proarrhythmic compounds, however the concentration at which action potential prolongation, triangulation, instability, reverse-use dependence and ectopic beats occurred often varied based on the concentration range selected. Further analysis using extended compound perfusion times demonstrated that variability may be due in part to lack of adequate equilibration of compound with the cardiac tissue.

DISCUSSION

We report that the model correctly identified proarrhythmic agents in a qualitative manner, but that study design impacts the proarrhythmic concentration derived from the model.

L-type calcium current recovery versus ventricular repolarization: preserved membrane-stabilizing mechanism for different QT intervals across species

BACKGROUND

Long QT syndrome is associated with early after-depolarization (EAD) that may result in torsade de pointes (TdP). Interestingly, the corrected QT interval seems to be proportional to body mass across species under physiologic conditions.

OBJECTIVE

The purpose of this study was to test whether recovery of L-type calcium current (I(Ca,L)), the primary charge carrier for EADs, from its inactivated state matches ventricular repolarization time and whether impairment of this relationship leads to development of EAD and TdP.

METHODS

Transmembrane action potentials from the epicardium, endocardium, or subendocardium were recorded simultaneously with a transmural ECG in arterially perfused left ventricular wedges isolated from cow, dog, rabbit, and guinea pig hearts. I(Ca,L) recovery was examined using action potential stimulation in isolated left ventricular myocytes.

RESULTS

The ventricular repolarization time (action potential duration at 90% repolarization [APD(90)]), ranging from 194.7 +/- 1.8 ms in guinea pig to 370.2 +/- 9.9 ms in cows, was linearly related to the thickness of the left ventricular wall among the species studied. The time constants (tau) of I(Ca,L) recovery were proportional to APD(90), making the ratios of tau to APD(90) fall into a relatively narrow range among these species despite markedly different ventricular repolarization time. Drugs with risk for TdP in humans were shown to impair this intrinsic balance by either prolongation of the repolarization time and/or acceleration of I(Ca,L) recovery, leading to the appearance of EADs capable of initiating TdP.

CONCLUSION

An adequate balance between I(Ca,L) recovery and ventricular repolarization serves as a "physiologic stabilizer" of ventricular action potentials in repolarization phases.

The Effect of Antihistamine Cetirizine on Ventricular Repolarization in Congenital Long QT Syndrome

INTRODUCTION

Many drugs are known to block cardiac potassium channels, thus prolonging QT interval and predisposing to malignant arrhythmias. Patients with congenital long QT syndrome are particularly vulnerable, but usually electrophysiological effects of drugs have not been assessed in these patients at risk.

METHODS

Fifteen asymptomatic patients with type 1 (LQT1), 15 patients with type 2 (LQT2) long QT syndrome, and 15 healthy volunteers took a placebo and cetirizine 10 mg. In addition, healthy volunteers took cetirizine 50 mg. The study was single-blinded and randomized. Exercise tests were performed during stable plasma concentrations. The electrocardiogram was recorded with a body surface potential mapping system (BSPM). Data were analyzed with an automated analyze program. QT intervals to the T wave apex and T wave end and their difference (Tp-e) were determined at rest and at specified heart rates during and after exercise.

RESULTS

Cetirizine did not lengthen the QT intervals at rest or during exercise and recovery in any group. It shortened Tp-e at rest in LQT1 and LQT2 patients and during exercise test in LQT1 patients, thus slightly decreasing electrocardiographic transmural dispersion of repolarization.

CONCLUSIONS

Cetirizine does not adversely modify ventricular repolarization in types 1 and 2 long QT syndrome, suggesting that it might be used safely in these long QT syndrome patients.