Exercise worsening of electromechanical disturbances: A predictor of arrhythmia in long QT syndrome

The Effects of Cycle Ergometer Versus Treadmill Exercise Stress Testing on QTc Interval Prolongation in Patients With Long QT Syndrome: A Systematic Review and Meta-analysis

OBJECTIVE

The safest and most effective exercise stress tests (EST) modalities for long QT syndrome (LQTS) are currently unknown. The main objective was to explore the effects of EST on the corrected QT interval (QTc) in patients with LQTS, and to compare the effects of different EST modalities (cycle ergometer vs treadmill).

DATA SOURCES

Systematic searches were performed in September 2022 in accordance with the PRISMA statement through PubMed, Medline, EBM Reviews, Embase, and Web of Science.

MAIN RESULTS

A total of 1728 patients with LQTS, whether congenital or acquired, without any age restrictions (pediatric age ≤18 years and adult age >19 years), and 2437 control subjects were included in the 49 studies. The QT interval data were available for 15 studies. Our analyses showed that the QT interval prolonged in a similar manner using either a cycle ergometer or a treadmill (standardized mean difference [SMD] = 1.89 [95% CI, 1.07-2.71] vs SMD = 1.46 [95% CI, 0.78-2.14], respectively). Therefore, it seems that either modality may be used to evaluate patients with LQTS.

CONCLUSIONS

The methodology for the measurement of the QT interval was very heterogeneous between studies, which inevitably influenced the quality of the analyses. Hence, researchers should proceed with caution when exploring and interpreting data in the field of exercise and LQTS.

The electromechanical window for arrhythmia-risk assessment

The electromechanical window (EMW) is calculated by subtracting the repolarization duration from a mechanical reference representing contraction duration in the same heartbeat (eg, aortic valve closure during echocardiography with simultaneous electrocardiography). Here, we review the current knowledge on the role of the EMW as an independent parameter for ventricular arrhythmia-risk stratification. We (1) provide a standardized approach to echocardiographic EMW assessment, (2) define relevant cutoff values for both abnormal EMW negativity and positivity, (3) discuss pathophysiological underpinnings of EMW negativity, and (4) outline the potential future role of cardiac electromechanical relations in patients with proarrhythmic conditions.

Reversed Apico-Basal Myocardial Relaxation Sequence During Exercise in Long QT Syndrome Mutations Carriers With History of Previous Cardiac Events

Background

Recent echocardiography studies in inherited long QT syndrome (LQTS) have shown left ventricular (LV) myocardial relaxation disturbances to follow markedly prolonged and dispersed mechanical contraction.

Aim

We used speckle-tracking echocardiography to assess disturbances in LV myocardial relaxation sequence during exercise and their relationship to symptoms.

Methods

Forty seven LQTS patients (45 ± 15 years, 25 female and 20 symptomatic, LVEF: 65 ± 6%) and 35 controls underwent exercise echocardiogram using Bruce protocol. ECG and echo parameters were recorded at rest, peak exercise (p.e.) and recovery.

Results

Between patients and controls there were no differences in age, gender, HR or LVEF. At p.e, patients had longer time to LV longitudinal E_SR (tE_SR) at all three LV segments; basal (p < 0.0001), mid- cavity (p = 0.03) and apical (p = 0.03) whereas at rest such difference was noted only at base (p = 0.0007). Patients showed reversed apico-basal relaxation sequence (ΔtE_{SRbase–apex}) with early relaxation onset occurring later at base than at apex, both at rest (49 ± 43 vs. –29 ± 19 ms, p < 0.0001) and at p.e. (46 ± 38 vs. –40 ± 22 ms, p < 0.0001), particularly in symptomatic patients (69 ± 44 vs. 32 ± 26, p < 0.0007). ΔtE_{SRbase–apex} correlated with longer QTc interval, lower E_SR and attenuated LV stroke volume.

Conclusion

LQTS patients show reversed longitudinal relaxation sequence, which worsens with exercise, particularly in those with previous cardiac events.

Exercise Induced Worsening of Mechanical Heterogeneity and Diastolic Impairment in Long QT Syndrome

BACKGROUND

Electromechanical heterogeneities due to marked dispersion of ventricular repolarisation and mechanical function have been associated with symptoms in long QT syndrome (LQTS) patients; Aim: To examine the exercise response of longitudinal LV systolic and diastolic myocardial function and synchronicity in LQTS patients and its relationship with symptoms; Methods: Forty seven (age 45 ± 15 yrs, 25 female, 20 symptomatic) LQTS patients and 35 healthy individuals underwent an exercise test (Bruce protocol). ECG and echo parameters were recorded at rest, peak exercise (p.e.), and recovery; Results: LQTS patients had prolonged and markedly dispersed myocardial contraction, delayed early relaxation phase, and significantly decreased filling time at all exercise phases. Unlike controls, these electromechanical disturbances deteriorated further with exercise, during which additional decrease of the LV diastolic myocardial function and attenuated LV stroke volume were noted. Such abnormal responses to exercise were seen to a greater degree in symptomatic patients and in the LQT1 subgroup and improved with B-blocker therapy. Worsening myocardial contraction dispersion at p.e. was the strongest discriminator for previous clinical events, and its discriminating power excelled further by adding early relaxation delay; Conclusions: Electromechanical disturbances were shown to worsen during exercise in LQTS patients and were more pronounced in those with previous arrhythmic events.

Exercise worsening of electromechanical disturbances: A predictor of arrhythmia in long QT syndrome

Background

Electromechanical (EM) coupling heterogeneity is significant in long QT syndrome (LQTS), particularly in symptomatic patients; EM window (EMW) has been proposed as an indicator of interaction and a better predictor of arrhythmia than QTc.

Hypothesis

To investigate the dynamic response of EMW to exercise in LQTS and its predictive value of arrhythmia.

Methods

Forty‐seven LQTS carriers (45 ± 15 years, 20 with arrhythmic events), and 35 controls underwent exercise echocardiogram. EMW was measured as the time difference between aortic valve closure on Doppler and the end of QT interval on the superimposed electrocardiogram (ECG). Measurements were obtained at rest, peak exercise (PE) and 4 minutes into recovery.

Results

Patients did not differ in age, gender, heart rate, or left ventricular ejection fraction but had a negative resting EMW compared with controls (−42 ± 22 vs 17 ± 5 ms, P < 0.0001). EMW became more negative at PE (−89 ± 43 vs 16 ± 7 ms, P = 0.0001) and recovery (−65 ± 39 vs 16 ± 6 ms, P = 0.001) in patients, particularly the symptomatic, but remained unchanged in controls. PE EMW was a stronger predictor of arrhythmic events than QTc (AUC:0.765 vs 0.569, P < 0.001). B‐blockers did not affect EMW at rest but was less negative at PE (BB: −66 ± 21 vs no‐BB: −113 ± 25 ms, P < 0.001). LQT1 patients had worse PE EMW negativity than LQT2.

Conclusion

LQTS patients have significantly negative EMW, which worsens with exercise. These changes are more pronounced in patients with documented arrhythmic events and decrease with B‐blocker therapy. Thus, EMW assessment during exercise may help improve risk stratification and management of LQTS patients.