Exercise-induced repolarization changes in patients with stable coronary artery disease

Disease Modifiers of Inherited SCN5A Channelopathy

To date, a large number of mutations in SCN5A, the gene encoding the pore-forming α-subunit of the primary cardiac Na⁺ channel (Na_V1.5), have been found in patients presenting with a wide range of ECG abnormalities and cardiac syndromes. Although these mutations all affect the same Na_V1.5 channel, the associated cardiac syndromes each display distinct phenotypical and biophysical characteristics. Variable disease expressivity has also been reported, where one particular mutation in SCN5A may lead to either one particular symptom, a range of various clinical signs, or no symptoms at all, even within one single family. Additionally, disease severity may vary considerably between patients carrying the same mutation. The exact reasons are unknown, but evidence is increasing that various cardiac and non-cardiac conditions can influence the expressivity and severity of inherited SCN5A channelopathies. In this review, we provide a summary of identified disease entities caused by SCN5A mutations, and give an overview of co-morbidities and other (non)-genetic factors which may modify SCN5A channelopathies. A comprehensive knowledge of these modulatory factors is not only essential for a complete understanding of the diverse clinical phenotypes associated with SCN5A mutations, but also for successful development of effective risk stratification and (alternative) treatment paradigms.

T-Wave Indices and Atherosclerosis

Tpeak-Tend interval, the time difference between the peak and the end of the T-wave, reflects the degree of dispersion of repolarization. Its prolongation has been associated with higher risks of developing ventricular arrhythmias and sudden cardiac death in different pro-arrhythmic conditions such as Brugada and long QT syndromes. In this review, we will provide a comprehensive overview on how Tpeak-Tend is altered in different atherosclerotic conditions such as hypertension, stable coronary artery disease, acute coronary obstruction, and coronary slow flow as well as inflammatory diseases affecting the arterial tree. We will explore its relationship with arterial function and dysfunction, ventricular remodeling, and arrhythmic and mortality outcomes. The published literature shows that patients with coronary atherosclerosis, whether in the form of stable coronary artery disease, chronic total occlusion, slow flow, or acute coronary obstruction, have prolonged Tpeak-Tend intervals and Tpeak-Tend/QT ratios. These can be used to predict the occurrence of ventricular arrhythmias and sudden cardiac death. They also correlate with the extent and severity of arterial stenosis and structural remodeling of the ventricles as well as arterial function and dysfunction. Finally, they can be normalized following revascularization and may therefore be used as a surrogate measure of treatment success.

The Role of Macrolide Antibiotics in Increasing Cardiovascular Risk

BACKGROUND

Large cohort studies provide conflicting evidence regarding the potential for oral macrolide antibiotics to increase the risk of serious cardiac events.

OBJECTIVES

This study performed a meta-analysis to examine the link between macrolides and risk of sudden cardiac death (SCD) or ventricular tachyarrhythmias (VTA), cardiovascular death, and death from any cause.

METHODS

We performed a search of published reports by using MEDLINE (January 1, 1966, to April 30, 2015) and EMBASE (January 1, 1980, to April 30, 2015) with no restrictions. Studies that reported relative risk (RR) estimates with 95% confidence intervals (CIs) for the associations of interest were included.

RESULTS

Thirty-three studies involving 20,779,963 participants were identified. Patients taking macrolides, compared with those who took no macrolides, experienced an increased risk of developing SCD or VTA (RR: 2.42; 95% CI: 1.61 to 3.63), SCD (RR: 2.52; 95% CI: 1.91 to 3.31), and cardiovascular death (RR: 1.31; 95% CI: 1.06 to 1.62). No association was found between macrolides use and all-cause death or any cardiovascular events. The RRs associated with SCD or VTA were 3.40 for azithromycin, 2.16 for clarithromycin, and 3.61 for erythromycin, respectively. RRs for cardiovascular death were 1.54 for azithromycin and 1.48 for clarithromycin. No association was noted between roxithromycin and adverse cardiac outcomes. Treatment with macrolides is associated with an absolute risk increase of 118.1 additional SCDs or VTA, and 38.2 additional cardiovascular deaths per 1 million treatment courses.

CONCLUSIONS

Administration of macrolide antibiotics is associated with increased risk for SCD or VTA and cardiovascular death but not increased all-cause mortality.

Impact of Percutaneous Coronary Intervention on Exercise-Induced Repolarization Changes in Patients With Stable Coronary Artery Disease

Recent reports suggest T peak to T end (Tpe) interval and Tpe/QT ratio as valuable indicators of increased arrhythmogenic risk in patients with coronary artery disease (CAD). We aimed to examine the exercise-induced changes in these indexes in patients with stable CAD, before and after percutaneous coronary intervention (PCI). Forty patients were consecutively included in the interventional group (n = 20), with significant lesions (≥75% luminal narrowing) suitable for PCI and in the control group (n = 20), with no significant coronary artery lesions (<50% luminal narrowing). One day before and 30 days after the coronarography, all patients performed treadmill exercise stress testing, and the electrocardiographic (ECG) indexes of repolarization were assessed during baseline and at peak exercise intensity. In the control group, the QT interval, QTc (QT-corrected) interval, Tpe interval, and Tpe/QT ratio measured at peak exercise significantly decreased from baseline values (p = 0.001, p = 0.004, p <0.001, and p = 0.017, respectively). Conversely, in interventional patients before the PCI, an increase in the Tpe interval and the Tpe/QT ratio was observed at exercise (p = 0.009, and p <0.001, respectively), with only the QT interval exhibiting a significant decrease from baseline (p <0.001). Thirty days after the PCI, all the ECG arrhythmogenic indexes measured at peak exercise significantly decreased from baseline values, thus assuming the same trend as detected in controls. In conclusion, restoration of blood supply normalized exercise-induced repolarization changes, suggesting that revascularization of previously ischemic myocardium lowers the cardiac arrhythmogenic potential in patients with stable CAD.

QT hysteresis index improves the power of treadmill exercise test in the screening of coronary artery disease

BACKGROUND

QT hysteresis phenomenon exists in healthy subjects, and is more exaggerated in patients with coronary artery disease (CAD) and long QT syndrome. The purpose of this study was to establish an appropriate method to evaluate the magnitude of QT hysteresis, and assess the value of QT hysteresis index in the treadmill exercise test (TET) in predicting CAD. METHODS AND RESULTS: A total of 138 subjects with suspected CAD and referred for TET and selective coronary angiography (SCA) were divided into positive (n=77) and negative (n=61) SCA groups. Dynamic ECG were recorded during TET. QT/RR curves were constructed and QTp (Q-Tpeak) and QTe (Q-Tend) hysteresis indices were calculated for each subject. SYNTAX score in the positive SCA group was determined. The QTp and QTe hysteresis indices in the positive SCA group were significantly higher than in the negative SCA group. The combination of QTe hysteresis index and conventional TET criteria had the highest sensitivity and negative predictive value according to receiver operating characteristic curve, and was an independent predictor on multivariate logistic regression. QT hysteresis indices significantly correlated with SYNTAX score in the positive SCA group.

CONCLUSIONS

QTe hysteresis index enhances the specificity of predicting CAD in TET. It improves the diagnostic value of TET for CAD significantly when combined with conventional criteria and is associated with the severity of CAD.

No association between high-density lipoprotein levels and ventricular repolarization indexes in subjects with primary hypercholesterolemia

OBJECTIVE

Data regarding the effect of lipid parameters on repolarization are sparse. Recent data indicate that reconstituted HDL administration shortens repolarization in cardiomyocytes as well as the corrected QT (QTc) interval in human subjects. We investigated the potential association of high-density lipoprotein cholesterol (HDL-C) levels with conventional and novel electrocardiographic markers of ventricular repolarization in patients with hypercholesterolemia.

METHODS

Consecutive subjects with primary hypercholesterolemia were recruited. We recorded clinical and laboratory parameters as well as electrocardiographic indexes. With regard to ventricular repolarization, we calculated the QTc interval, the T peak-to-end (Tpe) interval, and the Tpe/QT ratio.

RESULTS

The study population consisted of 440 patients (199 men) with a median age of 56 [48-65] years. The correlation analysis (Spearman's) failed to show any association between HDL-C and any of the studied electrocardiographic parameter. Moreover, no correlation between other lipid parameters and the electrocardiograhic indexes was evident. Also, a comparison of the ventricular repolarization parameters between different HDL-C quartile groups (HDL-Q1: ≤ 1.11 mmol/L; HDL-Q2: 1.12-1.29 mmol/L; HDL-Q3: 1.30-1.53 mmol/L; HDL-Q4: ≥ 1.54 mmol/L) was performed. Specifically, the differences in QTc (p: 0.372), Tpe in leads II (p: 0.356), V2 (p: 0.372), V5 (p: 0.112), and Tpe/QT in leads II (p: 0.348), V2 (p: 0.162), V5 (p: 0.122) were not significant.

CONCLUSION

HDL-C levels are not associated with the QTc interval or indexes of repolarization dispersion in patients with primary hypercholesterolemia. The potential antiarrhythmic efficacy of HDL should be further evaluated in the setting of myocardial ischemia where dynamic changes in the heterogeneity of ventricular repolarization ensue.

Ibutilide and novel indexes of ventricular repolarization in persistent atrial fibrillation patients

AIM: To examine the effect of ibutilide on novel indexes of repolarization in patients with persistent atrial fibrillation (AF).

METHODS: We studied consecutive patients scheduled for elective electrical cardioversion. Intravenous ibutilide (1 + 1 mg) was administered before the electrical cardioversion while close electrocardiographic (ECG) monitoring was performed. ECG indexes such as corrected QT interval (QTc), the interval from the peak until the end of T wave (Tpe), and the Tpe/QT ratio were measured before ibutilide infusion and 10 min after the end of infusion.

RESULTS: The final study population consisted of 20 patients (mean age: 67.1 ± 9.9 years, 10 men). Six patients were cardioverted pharmacologically and did not proceed to electrical cardioversion. Two patients developed short non-sustained episodes of torsades de pointes ventricular tachycardia. All but one of the aforementioned ECG indexes increased significantly after ibutilide administration. In specific, the QTc interval increased from 442 ± 29 to 471 ± 37 ms (P = 0.037), the Tpe interval in precordial leads from 96 ms (range 80-108 ms) to 101 ms (range 91-119 ms) (P = 0.021), the Tpe interval in lead II from 79 ms (range 70-88 ms) to 100 ms (range 87-104 ms) (P < 0.001), the Tpe/QT ratio in precordial leads from 0.23 ms (range 0.18-0.26 ms) to 0.26 ms (range 0.23-0.28 ms) (P = 0.028), and the Tpe interval dispersion from 25 ms (range 23-30 ms) to 35 ms (range 27-39 ms) (P = 0.012). However, the Tpe/QT ratio in lead II did not change significantly.

CONCLUSION: Ibutilide increases the duration and dispersion of ventricular repolarization. The prognostic value of Tpe and Tpe/QT in the setting of drug-induced proarrhythmia needs further study.

The impact of hemodialysis on the dispersion of ventricular repolarization

BACKGROUND

Sudden cardiac death is prevalent in chronic hemodialysis (HD) patients while the dialysis process may have arrhythmogenic potential. We sought to examine the effect of HD on conventional electrocardiographic parameters as well as on novel indexes of repolarization, given that increased spatial dispersion of repolarization is related to ventricular arrhythmias.

METHODS

We recorded clinical, echocardiographic, and laboratory parameters as well as electrocardiographic indexes before and after a single HD session. Specifically, we calculated the QTc interval, the QRS duration, the T peak-to-end (Tpe) interval, and the Tpe/QT ratio.

RESULTS

The study population consisted of 66 chronic HD patients (mean age: 68.9 ± 11.8 years, 40 males). Heart rate, blood pressure, QRS duration, QTc interval, and QT dispersion did not change significantly after the HD session. However, the Tpe interval and the Tpe/QT ratio increased significantly (80 [65-90] ms vs 85 [77.5-100] ms; P = 0.04, and 0.21 [0.18-0.24] vs 0.25 [0.21-0.28]; P = 0.05, respectively). Correlation analysis and multiple regression analysis failed to show significant associations between the baseline parameters and the baseline values of Tpe and Tpe/QT or between the change of the laboratory parameters during HD and the corresponding change of the Tpe and the Tpe/QT values. No significant arrhythmias were observed during the HD sessions.

CONCLUSIONS

HD induces an increase in novel markers of spatial dispersion of ventricular repolarization. Whether the assessment of these indexes of heterogeneity of repolarization at baseline or their change during HD has a prognostic value with regard to future untoward events, remains to be elucidated.

Dobutamine "stress" test and latent cardiac susceptibility to inhaled diesel exhaust in normal and hypertensive rats

BACKGROUND

Exercise "stress" testing is a screening tool used to determine the amount of stress for which the heart can compensate before developing abnormal rhythm or ischemia, particularly in susceptible persons. Although this approach has been used to assess risk in humans exposed to air pollution, it has never been applied to rodent studies.

OBJECTIVE

We hypothesized that a single exposure to diesel exhaust (DE) would increase the risk of adverse cardiac events such as arrhythmia and myocardial ischemia in rats undergoing a dobutamine challenge test, which can be used to mimic exercise-like stress.

METHODS

Wistar-Kyoto normotensive (WKY) and spontaneously hypertensive (SH) rats implanted with radiotelemeters and a chronic intravenous catheter were whole-body exposed to 150 μg/m3 DE for 4 hr. Increasing doses of dobutamine, a β1-adrenergic agonist, were administered to conscious unrestrained rats 24 hr later to elicit the cardiac response observed during exercise while heart rate (HR) and electrocardiogram (ECG) were monitored.

RESULTS

A single exposure to DE potentiated the HR response of WKY and SH rats during dobutamine challenge and prevented HR recovery at rest. During peak challenge, DE-exposed SH rats had lower overall HR variability when compared with controls, in addition to transient ST depression. All DE-exposed animals also had increased arrhythmias.

CONCLUSIONS

These results are the first evidence that rats exhibit stress-induced cardiac dysrhythmia and ischemia sensitivity comparable to humans after a single exposure to a toxic air pollutant, particularly when in the presence of underlying cardiovascular disease. Thus, exposure to low concentrations of air pollution can impair the heart's ability to respond to stress and increase the risk of subsequent triggered dysfunction.

Relation of ventricular ectopic complexes to QTc interval on ambulatory electrocardiograms in Williams syndrome

Williams syndrome (WS) is a congenital, developmental disorder affecting 1 in 8,000 live births. The corrected QT (QTc) interval is prolonged in 13% of patients with WS. No data exist characterizing the ambulatory electrocardiographic findings in WS. A retrospective review of all patients with WS evaluated at our institution from January 1, 1980 to December 31, 2007 was performed. Patients with ≥1 ambulatory electrocardiogram (AECG) with sinus rhythm and measurable intervals were included. QTc measurements were made at the minimum and maximum heart rate. Logistic regression analysis was used to evaluate the correlation of ventricular ectopic complexes with QTc measurements. A statistical probability of p <0.05 was considered significant. Of 270 patients identified, 32 had AECGs available for review. Complete data were available for 56 AECGs from 26 patients (15 female; 58%). Their mean age was 15.6 ± 7.2 years at the initial AECG and 20.6 ± 8.6 years for all AECGs. The QTc interval increased with increasing heart rate. Ventricular premature complexes occurred in 40 (73%) of 56 AECGs and 21 (81%) of 26 patients. Ventricular tachycardia occurred in 5 (9%) of 56 AECGs and 4 (15%) of 26 patients. The mean length of ventricular tachycardia was 3.6 ± 0.5 beats at a rate of 171 ± 40 beats/min. The QTc interval at the minimum heart rate correlated directly with age (p <0.001), total ventricular premature complexes (p = 0.007), ventricular couplets (p = 0.002), and ventricular tachycardia (p = 0.011). The QTc interval at the maximum heart rate correlated directly with age (p <0.001), total ventricular premature complexes (p = 0.016), and ventricular couplets (p = 0.006). In conclusion, the QTc interval correlated with ventricular ectopic complexes in patients with WS. The type of ventricular ectopic complexes suggested an alternate etiology of the QTc prolongation seen in WS from that seen in congenital long QT syndrome.

Novel indexes of heterogeneity of ventricular repolarization in subjects with early repolarization pattern

AIM

The presence of early repolarization (ER) in inferior or inferolateral leads has been associated with malignant arrhythmias and increased mortality. Transmural dispersion of repolarization (TDR) has been proposed to underlie arrhythmogenesis in J-wave syndromes. The present study investigated specific electrocardiographic (ECG) markers including Tpeak-Tend interval and (Tpeak-Tend)/QT ratio that reflect TDR in subjects with ER.

METHODS AND RESULTS

The ECGs of 47 healthy individuals (43 males, mean age: 45.7 ± 13.1 years) with an ER pattern in lateral (n = 15) or infero-lateral leads (n = 32) who successfully completed an exercise stress test were analysed at rest, peak workload, and recovery. The ER pattern was defined as slurring or notching of the terminal part of the QRS complex (J-point) ≥ 1 mm, in at least two contiguous leads. Thirty-five age- and sex-matched healthy subjects without ER (28 males, mean age: 48.6 ± 10.2 years) served as comparative controls. Subjects with ER displayed increased Tpeak-Tend interval in lead V(2), Tpeak-Tend dispersion of the precordial leads, and (Tpeak-Tend)/QT ratio in lead V(2) compared with those without ER in all three phases of the exercise test (P < 0.05). In addition, Tpeak-Tend dispersion and the (Tpeak-Tend)/QT ratio in lead V(2) were significantly increased at recovery phase compared with peak exercise only in subjects with ER (P< 0.05). There were no significant differences among the studied ECG parameters regarding the ER location (lateral vs. infero-lateral), the ER type (slurring or notching), or the maximum J-point amplitude (≥ 1.5 vs. <1.5 mm) at baseline ECGs.

CONCLUSIONS

Individuals with ER display an increased TDR that may be related to an increased arrhythmic risk.