Repolarization changes in patients with heart failure receiving cardiac resynchronization therapy—signs of cardiac memory

Predictive value of frontal QRS-T angle after cardiac resynchronization therapy

OBJECTIVE

It is practical and useful to detect patients who benefit from cardiac resynchronization therapy (CRT) by electrocardiographic (ECG) methods. In this study, the predictive role of the frontal QRS-T angle and other ECG parameters was evaluated in CRT responder patients.

METHOD

Seventy-seven consecutive patients with left ventricular ejection fraction (LVEF) ≤ 35%, New York Heart Association (NYHA) classes II-III, ambulatory class IV and normal sinus rhythm, who had complete left bundle branch block and were treated with CRT were included in this study. Patients were classified as "CRT responders" and "CRT non responders" according to their LVEF improvement. The frontal QRS-T angle was calculated as the absolute value of the difference between the QRS and T wave axes [frontal QRS-T angle = (QRS axis-T axis)].

RESULTS

The mean age of the patients was 64.5 ± 9.1 years, and the average follow-up was 28 (12-47) months. The post-implantation LVEF was higher in the patients CRT responders group (p < 0.001). Post-implantation frontal QRS-T angle (p = 0.003), QRS duration (p = 0.008) and cQT interval (p = 0.012) values were much shorter in the CRT responder group. Multivariable regression analyses showed that the frontal QRS-T angle and age were independent risk factors for CRT response (p = 0.009). The results of the receiver operating characteristic curve analyses (ROC) showed that the predictive optimal cut-off value of CRT response for the frontal QRS-T angle was <135 degrees (AUC: 0.69, 95% CI 0.575-0.814, p = 0.004).

CONCLUSION

The narrowed frontal QRS-T angle (<135 degrees), QRS duration and cQT interval were associated with CRT response in heart failure patients. The frontal QRS-T angle can be an independent predictor of CRT response.

Characteristics of Cardiac Memory in Patients with Implanted Cardioverter-defibrillators: The Cardiac Memory with Implantable Cardioverter-defibrillator (CAMI) Study

This study sought to determine factors associated with cardiac memory (CM) in patients with implantable cardioverter-defibrillators (ICDs). Patients with structural heart disease [n = 20; mean age: 72.6 ± 11.6 years; 80% male; mean left ventricular ejection fraction (LVEF): 31.7 ± 7.6%; history of myocardial infarction in 75% and nonsustained ventricular tachycardia (NSVT) in 85%] and preserved atrioventricular conduction received dual-chamber ICDs for primary (80%) or secondary (20%) prevention. Standard 12-lead electrocardiograms were recorded in AAI and DDD modes before and after seven days of right ventricular (RV) pacing in DDD mode with a short atrioventricular delay. The direction (azimuth and elevation) and magnitude of spatial QRS, T, and spatial ventricular gradient vectors were measured before and after seven days of RV pacing. CM was quantified as the degree of alignment between QRS_DDD-7 and T_AAI-7 vectors (QRS_DDD-7 –T_AAI-7 angle). Circular statistics and mixed models with a random slope and intercept were adjusted for changes in cardiac activation, LVEF, known risk factors, and the use of medications known to affect CM occurring on days 1 through 7. The QRS_DDD-7–T_AAI-7 angle strongly correlated (circular r = −0.972; p < 0.0001) with a T_AAI-7–T_DDD-7 angle. In the mixed models, CM-T azimuth changes [+132° (95% confidence interval (CI): 80°–184°); p < 0.0001] were counteracted by the history of MI [−180° (95% CI: −320° to −40°); p = 0.011] and female sex [−162° (95% CI: −268° to −55°); p = 0.003]. A CM-T area increase [+15 (95% CI: 6–24) mV*ms; p < 0.0001] was amplified by NSVT history [+27 (95% CI: 4–46) mV*ms; p = 0.007]. These findings suggest that preexistent electrical remodeling affects CM in response to RV pacing, that CM exhibits saturation behavior, and that women reach CM saturation more easily than men.

Reversion of cardiac memory during left bundle branch pacing

Cardiac memory (CM) is identified as an altered T wave when normal ventricular activation resumes after an abnormal myocardial activation period. We present a case who initially underwent temporary right ventricular apex (RVA) pacing for one week which induced typical pseudo-primary T wave changes. The T wave inversion was observed after the end of RVA pacing when left bundle branch pacing (LBBP) was initiated, and the abnormal T waves gradually return to almost normal repolarization during LBBP 40 days later.

Reduced T wave alternans in heart failure responders to cardiac resynchronization therapy: Evidence of electrical remodeling

Background

T-wave alternans (TWA), a marker of electrical instability, can be modulated by cardiac resynchronization therapy (CRT). The relationship between TWA and heart failure response to CRT has not been clearly defined.

Methods and results

In 40-patients (age 65±11 years, left ventricular ejection-fraction [LVEF] 23±7%), TWA was evaluated prospectively at median of 2 months (baseline) and 8 months (follow-up) post-CRT implant. TWA-magnitude (V_alt >0μV, k≥3), its duration (d), and burden (V_alt ·d) were quantified in moving 128-beat segments during incremental atrial (AAI, native-TWA) and atrio-biventricular (DDD-CRT) pacing. The immediate and long-term effect of CRT on TWA was examined. Clinical response to CRT was defined as an increase in LVEF of ≥5%. Native-TWA was clinically significant (V_alt ≥1.9μV, k≥3) in 68% of subjects at baseline. Compared to native-TWA at baseline, DDD-CRT pacing at baseline and follow-up reduced the number of positive TWA segments, peak-magnitude, longest-duration and peak-burden of TWA (44±5 to 33±5 to 28±4%, p = 0.02 and 0.002; 5.9±0.8 to 4.1±0.7 to 3.8±0.7μV, p = 0.01 and 0.01; 97±9 to 76±8 to 67±8sec, p = 0.004 and <0.001; and 334±65 to 178±58 to 146±54μV.sec, p = 0.01 and 0.004). In addition, the number of positive segments and longest-duration of native-TWA diminished during follow-up (44±5 to 35±6%, p = 0.044; and 97±9 to 81±9sec, p = 0.02). Clinical response to CRT was observed in 71% of patients; the reduction in DDD-CRT paced TWA both at baseline and follow-up was present only in responders (interaction p-values <0.1).

Conclusion

Long-term CRT reduces the prevalence and magnitude of TWA. This CRT induced beneficial electrical remodeling is a marker of clinical response after CRT.

Repolarization heterogeneity in patients with cardiac resynchronization therapy and its relation to ventricular tachyarrhythmias

BACKGROUND

Cardiac resynchronization therapy (CRT) has been shown to induce left ventricular reverse remodeling, but little is known about its influence on ventricular repolarization.

OBJECTIVE

The purpose of this study was to evaluate changes in ventricular repolarization of native conduction after CRT and its relation to ventricular tachycardia (VT) and ventricular fibrillation (VF) during long-term follow-up.

METHODS

We prospectively included 64 patients with heart failure treated with CRT. QT interval, TpTe, and TpTe/QT ratio were analyzed from 20-minute high-resolution ECGs that were recorded at baseline and 1, 3, 6, 9, and 12 months after CRT implantation. CRT was temporary inhibited during follow-up to record intrinsic ECG. Patients with a decrease of left ventricular end-systolic volume ≥15% at 12-month follow-up (mid-term follow-up) were considered as responders. Occurrences of VT/VF during follow-up were noted.

RESULTS

Significant increase of repolarization heterogeneity in the first months after implantation was observed (P <.05) but then declined during 12 months of follow-up. Patients with VT/VF during long-term follow-up had higher repolarization heterogeneity at mid-term follow-up than patients without VT/VF (TpTe/QT ratio: 0.263 [0.204-0.278] vs 0.225 [0.204-0.239]; P = .045). Echocardiographic response at mid-term follow-up did not significantly influence the rate of VT/VF (log-rank P = .252). In multivariate Cox regression analysis, only high repolarization heterogeneity at mid-term follow-up (TpTe/QT ratio >0.260) was independently associated with high risk of VT/VF (hazard ratio 4.29; 95% confidence interval 1.40-13.15; P = .011).

CONCLUSION

CRT induces time-dependent changes in repolarization parameters in the first year after implantation. High repolarization heterogeneity at mid-term follow-up was associated with higher rate of VT/VF during long-term follow-up.

Pathophysiology of dyssynchrony: of squirrels and broken bones

The genesis of cardiac resynchronisation therapy (CRT) consists of 'bedside' research and 'bench' studies that are performed in series with each other. In this field, the bench studies are crucial for understanding the pathophysiology of dyssynchrony and resynchronisation. In a way, CRT started with the insight that abnormal ventricular conduction, as caused by right ventricular pacing, has adverse effects. Out of this research came the ground-breaking insight that 'simple' disturbances in impulse conduction, which were initially considered innocent, proved to result in a host of molecular and cellular derangements that lead to a vicious circle of remodelling processes that facilitate the development of heart failure. As a consequence, CRT does not only correct conduction abnormalities, but also improves myocardial properties at many levels. Interestingly, corrections by CRT do not exactly reverse the derangements, induced by dyssynchrony, but also activate novel pathways, a property that may open new avenues for the treatment of heart failure.

Comparison of the Effects of Epicardial and Endocardial Cardiac Resynchronization Therapy on Transmural Dispersion of Repolarization

BACKGROUND

Despite significant improvements in cardiac output and functional capacity with cardiac resynchronization therapy (CRT), incidence of sudden cardiac death still remains high. Reversal of physiological myocardial activation sequence during epicardial pacing increases the transmural dispersion of repolarization (TDR). The aim of this study was to compare the effects of endocardial and epicardial biventricular pacing on repolarization parameters in the same patient group.

METHODS

Seven patients who had transseptal endocardial left ventricle (LV) lead placement, in whom epicardial CRT had failed due to coronary sinus (CS) lead dislodgement after successful implantation, were admitted to the study. LV endocardial leads were implanted through the interatrial septum in a lateral position. Electrocardiograms (ECGs) were scanned before and after successful epicardial and endocardial biventricular pacing and analyzed using digital calipers. ECG markers of TDR (TpTe and TpTe/QT ratio) were measured and compared.

RESULTS

Baseline QRS durations (161.7 ± 15.9 ms vs 162.2 ± 17.8 ms, P = 0.95), TpTe values (107.1 ± 20.5 ms vs 108.5 ± 17.6 ms, P = 0.89), and TpTe/QT ratios (0.24 ± 0.05 vs 0.24 ± 0.03, P = 0.88) were similar before epicardial and endocardial CRT. QRS interval reduction was similar (-28.3 ± 11.6 ms vs -29.1 ± 11.4 ms, P = 0.89) in both groups. Compared to transseptal endocardial CRT, epicardial CRT was associated with a significant increase in TpTe (17.1 ± 19.5 ms vs -12.6 ± 18.9 ms, P = 0.01) and TpTe/QT ratio (0.03 ± 0.04 vs -0.02 ± 0.03, P = 0.04).

CONCLUSION

Transseptal LV endocardial pacing is associated with significant reduction in TDR characteristics compared to epicardial pacing in CRT. Further studies are warranted to determine whether these effects may contribute to reduction of arrhythmias in patients with CRT.

Cardiac memory in cardiac resynchronization therapy: A vectorcardiographic comparison of biventricular and left ventricular pacing

INTRODUCTION

"Cardiac memory" (CM) refers to a change in repolarization induced by an altered pathway of activation, manifested after resumption of spontaneous ventricular activation (SVA).

AIMS

To investigate for the first time in humans the effects of left ventricular (LV) pacing on CM development through vectorcardiography (VCG).

METHODS

We studied 28 patients with heart failure (HF) and left bundle branch block (LBBB) treated with cardiac resynchronization therapy (CRT). Fourteen patients underwent biventricular (BIV) stimulation; the other 14 underwent LV stimulation only. VCG was acquired during SVA at baseline and during AAI and DDD pacing immediately after and 7 and 90 days after the implant.

RESULTS

At baseline, in both groups, the QRS and T vectors angles were those specific of LBBB pattern. During DDD pacing, QRS vector angle changed to the right and upward in BIV patients while no significant differences were observed in LV patients. During AAI pacing, T vector angle changed significantly in BIV patients, following the direction of the paced QRS and amplitude significantly increased. In LV patients no significant differences in T vector angles were observed. Only T vector amplitude significantly increased at 7 days (p=0.03) and at 90 days (p=0.008 vs baseline).

CONCLUSION

In patients with LBBB, BIV pacing induces cardiac memory development as a significant change in T vector magnitude and angle, while LV pacing doesn't induce significant modifications in QRS and T vector angles and CM is manifested only as a significant T vector amplitude change.

Cardiac memory during rather than after termination of left bundle branch block

An 83-year-old woman with chronic left bundle branch block and remote history of pacemaker implantation for intermittent AV block was hospitalized for fatigue and leg swelling. She had no cardiac complaints. Routine 12-lead electrocardiogram showed sinus rhythm with left bundle branch block. There were diffuse negative T waves in the inferior and anterolateral leads that were concordant with the QRS complexes. Echocardiogram was normal and nuclear perfusion heart scan showed no abnormality. It was noted that the negative T waves during left bundle branch block were in the exact same leads as were the deep negative QRS complexes during ventricular pacing. The electrocardiographic changes were consistent with cardiac memory. This case is unique because cardiac memory in patients with intermittent left bundle branch block typically occurs when the QRS complexes normalize and not during left bundle branch block itself. Our findings indicate that memory Ts can develop not only after normalization of wide complex rhythms but also with alternating wide complex rhythms as in the presented case where a ventricular paced rhythm was replaced by left bundle branch block.

Mechano-electrical coupling as framework for understanding functional remodeling during LBBB and CRT

It is not understood why, after onset of left bundle-branch block (LBBB), acute worsening of cardiac function is followed by a further gradual deterioration of function, whereas most adverse cardiac events lead to compensatory adaptations. We investigated whether mechano-electrical coupling (MEC) can explain long-term remodeling with LBBB and cardiac resynchronization therapy (CRT). To this purpose, we used an integrative modeling approach relating local ventricular electrophysiology, calcium handling, and excitation-contraction coupling to global cardiovascular mechanics and hemodynamics. Each ventricular wall was composed of multiple mechanically and electrically coupled myocardial segments. MEC was incorporated by allowing adaptation of L-type Ca2+ current aiming at minimal dispersion of local external work, an approach that we previously applied to replicate T-wave memory in a synchronous heart after a period of asynchronous activation. LBBB instantaneously decreased left-ventricular stroke work and increased end-diastolic volume. During sustained LBBB, MEC reduced intraventricular dispersion of mechanical workload and repolarization. However, MEC-induced reduction in contractility in late-activated regions was larger than the contractility increase in early-activated regions, resulting in further decrease of stroke work and increase of end-diastolic volume. Upon the start of CRT, stroke work increased despite a wider dispersion of mechanical workload. During sustained CRT, MEC-induced reduction in dispersion of workload and repolarization coincided with a further reduction in end-diastolic volume. In conclusion, MEC may represent a useful framework for better understanding the long-term changes in cardiac electrophysiology and contraction following LBBB as well as CRT.

Modeling cardiac electromechanics and mechanoelectrical coupling in dyssynchronous and failing hearts: insight from adaptive computer models

Computer models have become more and more a research tool to obtain mechanistic insight in the effects of dyssynchrony and heart failure. Increasing computational power in combination with increasing amounts of experimental and clinical data enables the development of mathematical models that describe electrical and mechanical behavior of the heart. By combining models based on data at the molecular and cellular level with models that describe organ function, so-called multi-scale models are created that describe heart function at different length and time scales. In this review, we describe basic modules that can be identified in multi-scale models of cardiac electromechanics. These modules simulate ionic membrane currents, calcium handling, excitation-contraction coupling, action potential propagation, and cardiac mechanics and hemodynamics. In addition, we discuss adaptive modeling approaches that aim to address long-term effects of diseases and therapy on growth, changes in fiber orientation, ionic membrane currents, and calcium handling. Finally, we discuss the first developments in patient-specific modeling. While current models still have shortcomings, well-chosen applications show promising results on some ultimate goals: understanding mechanisms of dyssynchronous heart failure and tuning pacing strategy to a particular patient, even before starting the therapy.