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Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
Published on: December 11, 2017
Repercussions of cardiac resynchronization therapy on the ventricular repolarization of heart failure patients as
Carlos Alberto Pastore1, Roberto A Douglas, Nelson Samesima
1Electrocardiology Service, Heart Institute (InCor) of the University of Sao Paulo Medical School, Sao Paulo, Brazil. ecg_pastore@incor.usp.br
Insights
Cardiac resynchronization therapy (CRT) significantly reduced QT dispersion and transmural dispersion of repolarization in heart failure patients with LBBB. This suggests CRT improves ventricular repolarization homogeneity, potentially explaining treatment benefits.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Devices
Background:
- Cardiac resynchronization therapy (CRT) is a treatment for heart failure (HF) patients with left bundle-branch block (LBBB) refractory to medical therapy.
- A significant portion of patients (nearly one-third) do not respond to CRT, and the underlying reasons remain unclear.
- Epicardial left ventricle (LV) pacing has been associated with adverse effects, including increased QT interval and dispersion, raising arrhythmia risk.
Purpose of the Study:
- To assess the impact of CRT on ventricular repolarization dispersion using body surface potential mapping (BSPM).
- To investigate changes in QT dispersion and transmural dispersion of repolarization during CRT in heart failure patients with LBBB.
Main Methods:
- A cohort of 60 NYHA class III-IV heart failure patients with LBBB received CRT via atrial-biventricular pacemakers.
- 87-lead body surface potential mapping (BSPM) was employed to analyze QT intervals, Tpeak-end intervals, and dispersion (QTd, transmural dispersion) at baseline and during CRT.
Main Results:
- CRT significantly reduced QT dispersion by 19.6% compared to baseline (85.58±26.63 msec vs. 68.83±25.16 msec, p=0.0009).
- Transmural dispersion of repolarization also decreased during CRT (55.50±15.45 msec vs. 49.41±14.11 msec, p=0.0343), though with smaller statistical significance.
Conclusions:
- The findings support the hypothesis that CRT improves electrical dispersion and homogeneity of cardiac ventricular repolarization.
- Electrocardiographic parameters derived from BSPM, specifically QT and Tpeak-end intervals, are valuable for studying CRT's effects on repolarization.
Objective:
Cardiac resynchronization therapy (CRT) is an adjunct treatment for heart failure (HF) which associates with left bundle-branch block (LBBB) and is refractory to medical therapy. However, nearly 1/3 of the patients still do not respond, the reasons for which have yet to be determined. Additionally, experimental studies proved that epicardial left ventricle (LV) pacing yields reversed electrical activation sequence, increasing QT interval duration and dispersion of the ventricular repolarization, and leaving patients at greater risk for ventricular arrhythmias.
Methods:
In this study, a series of 60 patients (61.7% male, mean age 59.2+/-11.54 years) in NYHA functional class III-IV heart failure and LBBB, who received CRT through implantation of atrial-biventricular pacemakers, were assessed by 87-lead body surface potential mapping (BSPM). The BSPM, noninvasive technique with semi-automatic readings, allowed analysis of variables associated with the cardiac ventricular repolarization QT intervals, maximal, minimum and mean Tpeak-end, and QT dispersion (QTmax - min), in addition to transmural dispersion of repolarization (Tpeak-end max - Tpeak-end min), in two different moments: baseline rhythm and during atrial-biventricular pacing.
Results:
QT dispersion showed a significant 19.6% reduction (p=0.0009) under CRT, as compared with baseline measurements (85.58+/-26.63 msec vs. 68.83+/-25.16 msec). The transmural dispersion of repolarization (Tpeak-end max - Tpeak-end min) showed smaller statistical significance (p=0.0343); however, its values were similarly decreased (55.50+/-15.45 msec vs 49.41+/-14.11 msec) during CRT.
Conclusion:
These results may corroborate findings from major randomized clinical trials. We consider that the electrocardiographic variables obtained with the use of the BSPM, namely, the QT and Tpeak-end intervals, are appropriate for analysis and study of the effects of cardiac resynchronization therapy on the improved electrical dispersion as characterizing the improvement of homogeneity of cardiac ventricular repolarization.
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