The Benefits of Biventricular Pacing in Heart Failure Patients with Narrow QRS, NYHA Class II and Right Ventricular Pacing

Presence of mechanical dyssynchrony in Duchenne muscular dystrophy

BACKGROUND

Cardiac dysfunction in boys with Duchenne muscular dystrophy (DMD) is a leading cause of death. Cardiac resynchronization therapy (CRT) has been shown to dramatically decrease mortality in eligible adult population with congestive heart failure. We hypothesized that mechanical dyssynchrony is present in DMD patients and that cardiovascular magnetic resonance (CMR) may predict CRT efficacy.

METHODS

DMD patients (n = 236) were stratified into 4 groups based on age, diagnosis of DMD, left ventricular (LV) ejection fraction (EF), and presence of myocardial fibrosis defined as positive late gadolinum enhancement (LGE) compared to normal controls (n = 77). Dyssynchrony indices were calculated based on timing of CMR derived circumferential strain (ecc). The calculated indices included cross-correlation delay (XCD), uniformity of strain (US), regional vector of variance (RVV), time to maximum strain (TTMS) and standard deviation (SD) of TTMS. Abnormal XCD value was defined as > normal + 2SD. US, RVV, TTMS and SD were calculated for patients with abnormal XCD.

RESULTS

There was overall low prevalence of circumferential dyssynchrony in the entire DMD population; it increased to 17.1% for patients with abnormal EF and to 31.2% in the most advanced stage (abnormal EF with fibrosis). All but one DMD patient with mechanical dyssynchrony exhibited normal QRS duration suggesting absence of electrical dyssynchrony. The calculated US and RVV values (0.91 ± 0.09, 1.34 ± 0.48) indicate disperse rather than clustered dyssynchrony.

CONCLUSION

Mechanical dyssynchrony is frequent in boys with end stage DMD-associated cardiac dysfunction. It is associated with normal QRS complex as well as extensive lateral fibrosis. Based on these findings, it is unlikely that this patient population will benefit from CRT.

Does biventricular pacing improve hemodynamics in children undergoing routine congenital heart surgery?

Biventricular (BiV) pacing or cardiac resynchronization therapy (CRT) is an established therapy for heart failure in adults. In children, cardiac dyssynchrony occurs most commonly following repair of congenital heart disease (CHD) where multisite pacing has been shown to improve both hemodynamics and ventricular function. Determining which patient types would specifically benefit has not yet been established. A prospective, repeated measures design was undertaken to evaluate BiV pacing in a cohort of children undergoing biventricular repair for correction of their CHD. Hemodynamics, arterial blood gas, electrocardiographic (ECG), and echocardiographic data were collected. Pacing protocol was undertaken prior to the patient's extubation with 20 min of conventional right ventricular (RV) or BiV pacing, preceded and followed by 10 min of recovery time. Multivariate statistics were used to analyze the data with p values <0.05 considered significant. Twenty-five (14 female) patients underwent surgery at a median (range) age of 5.2 (0.1-37.4) months with no early mortality. The Risk-adjusted classification for Congenital Heart Surgery (RACHS) scores were 2 in 14 patients, 3 in eight patients, and 4 in three patients. None had pre-existing arrhythmias, dyssynchrony, or required pacing pre-operatively. No patient required implantation of a permanent pacemaker post-operatively. The median cardio-pulmonary bypass time was 96 (55-236) min. RV and BiV pacing did not improve cardiac index from baseline (3.23 vs. 3.42 vs. 3.39 L/min/m2; p > 0.05). The QRS duration was not changed with pacing (100 vs. 80 vs. 80 ms; p > 0.05). On echocardiography, the time-to-peak velocity difference between the septal and posterior walls (synchrony) during pacing was similar to baseline and was also not statistically significant. BiV pacing did not improve cardiac output when compared to intrinsic sinus rhythm or RV pacing in this cohort of patients. Our study has shown that BiV pacing is not indicated in children who have undergone routine BiV congenital heart surgery. Further prospective studies are needed to assess the role of multisite pacing in children with ventricular dyssynchrony such as those with single ventricles, those undergoing reoperation or those with high RACHS scores.

Time course of effects of cardiac resynchronization therapy in chronic heart failure: benefits in patients with preserved exercise capacity

OBJECTIVES

To assess in patients with chronic heart failure the effect of cardiac resynchronization therapy (CRT) over 12 months' follow-up the time course of the changes in functional and neurohormonal indices and to identify responders to CRT.

METHODS

Eighty-nine patients (74.1 +/- 1 years, left ventricular ejection fraction [LVEF] < 35%), QRS complex duration >150 ms, in stable New York Heart Association (NYHA) class III or IV on optimal medical treatment were prospectively randomized either in a control (n = 45) or CRT (n = 44) group and underwent clinical evaluation, cardiopulmonary exercise testing (CPET), 2D-Echo, heart rate variability (HRV), carotid baroreflex (BRS), and BNP assessments before and at 6- and 12-month follow-up.

RESULTS

In the CRT group, improvement of cardiac indices and BNP concentration were evident at medium term (over 6 months) follow-up, and these changes persisted on a longer term (12 months) (all P < 0.05). Instead CPET indices and NYHA class improved after 12 months associated with restoration of HRV and BRS (all P < 0.05). We identified 26 responders to CRT according to changes in LVEF and diameters. Responders presented less depressed hemodynamic (LVEF 25 +/- 1.0 vs 22 +/- 0.1%), functional (peak VO(2) 10.2 +/- 0.2 vs 6.9 +/- 0.3 ml/kg/min), and neurohormonal indices (HRV 203.6 +/- 15.7 vs 147.6 +/- 10.ms, BRS 4.9 +/- 0.2 vs 3.6 +/- 0.3 ms/mmHg) (all P < 0.05). In the multivariate analysis, peak VO(2) was the strongest predictor of responders.

CONCLUSIONS

Improvement in functional status is associated with restoration of neurohormonal reflex control at medium term. Less depressed functional status (peak VO(2)) was the strongest predictor of responders to CRT.