Conventional right ventricular (RV) apical pacing has been indicated to have deleterious effect on left ventricular (LV) systolic function.1 Biventricular (BiV) pacing and cardiac resynchronization therapy (CRT) has been found to arrest decline of LV systolic function and prevent cardiac remodeling in patients with heart failure. A widened QRS complex on electrocardiogram (ECG) of a patient with chronic heart failure has been demonstrated to indicate worsening of LV systolic function2 as well as correlated with an increased risk of death.3,4,5 Biventricular pacing has been postulated to have a beneficial effect on symptoms of patients with medically refractory chronic heart failure and widened QRS complex.6 It has been suggested that non-ischemic cardiomyopathy (NICM) patients with CRT have a better prognosis than those with ischemic cardiomyopathy.7 Our study aimed to evaluate if CRT therapy improved QRS duration, and to what extent, within 24 hours of biventricular pacemaker insertion in subjects with NICM having a left bundle branch block pattern (LBBB) on ECG. The study also aimed to evaluate if presence of atrial fibrillation/flutter contributed to observed outcome.
Eighteen patients (mean age 67.3 yrs) with NICM––four women and 14 men—with left bundle branch block (LBBB) pattern on ECG, that underwent biventricular pacemaker implantation for CRT between June, 2009 and December, 2009 were included. Four subjects (three men and one woman) were on prior RV pacing, which produced the LBBB pattern on ECG, and were receiving an upgrade to bi-ventricular pacing and CRT. The other 14 subjects included had LBBB pattern on ECGs and were eligible for de novo CRT with bi-ventricular pacing because of NICM. ECGs of subjects were done 24 hours before receiving CRT as well as within 24 hours after bi-ventricular pacemaker implantation, and tracings were compared for changes in QRS duration. Also, prior atrial fibrillation/flutter was noted. The mean values of QRS duration from three blinded observations were tabulated and analyzed to eliminate inter-observer variability.
All data were recorded as mean ± standard deviation of triplicate measurements. Significance of differences among treatment means was determined by one-way ANOVA at p<0.05. Results analyzed for correlation and regression were tested for significance by Student’s t-test (p<0.05) using MATLAB 7.0 (Natick, MA, US) and Microsoft Excel 2007 (Roselle, IL, US).
A total of 18 subjects, with a mean age of 67.3 years, with NICM were included. Four subjects (three men and one woman), on prior RV pacing for different reasons, were upgraded to CRT. Fourteen subjects (11 men and three women) received de novo CRT with biventricular pacing. Three subjects in the upgrade group (75 %) and four subjects (28.57 %) in the de novo CRT group had prior atrial fibrillation/flutter. Mean improvement in QRS duration in the group on prior RV pacing was found to be 29 ± 20.54 ms (n=4); while that in de novo CRT group was 12.4 ± 22.58 ms (n=14). Those with prior atrial fibrillation/flutter in the upgrade group had a mean improvement in QRS duration of 22.33 ± 19.14 ms (n=3); those in de novo bi-ventricular pacing group had a mean improvement in QRS duration of 10.5 ± 9.15 ms (n=4), while those not having prior atrial fibrillation/flutter in the de novo CRT group had a mean QRS duration improvement of 8.22 ± 22.71 ms (n=10). All subject groups showed a decrease in QRS duration. However, one-way ANOVA confirmed that the impact of CRT on QRS duration improvement in patients did not depend on whether subjects had a de novo BiV/LBBB owing to prior RV pacing; also QRS duration improvement in patients is not contingent on atrial fibrillation in patients undergoing CRT. The following groups––atrial fibrillation (AFIB) plus prior RV pacemaker, non-AFIB plus RV pacemaker, AFIB plus de novo BiV-CRT and non-AFIB plus de novo BiV-CRT––showed no significant difference in QRS duration improvement, over any other single group (see Table 1).
There was an observed significant negative correlation (r = -0.49; y = -0.004x + 0.41; p<0.05) between age (x) and percentage decrease in QRS (y). This means that there was a consistent decline in the rate of QRS duration decrease in patients with increasing age (see Figure 1).
The study investigated whether CRT significantly improved mean QRS duration within 24 hours in subjects having LBBB patterns on pre-procedural ECG before the initiation of CRT. Our data showed that there was no statistically significant superiority in improvement in the QRS duration between subjects with prior RV pacing and those receiving a de novo bi-ventricular pacemaker. Prior presence of atrial fibrillation/flutter also did not confer additional benefits between two groups. However, use of CRT, in subjects having LBBB on ECG at a younger age, seems to improve the QRS duration within 24 hours of CRT to a greater extent than later initiation.
A number of recent studies have reached a similar conclusion as CRT has been seen to improve and even reverse cardiac remodeling in patients in early stage of heart failure (NYHA I/II).8,9 Therefore, early detection of heart failure, especially in non-ischemic young patients with mild heart failure, a reduced LV ejection fraction, a wide QRS duration (>150 ms), and early initiation of CRT might arrest and even reverse LV remodeling.10
Limitations of the study include a small sample size, short follow-up, assessment of QRS duration was only used in determining improvement in ventricular asynchrony, and the possible confounding effect of increased age on QRS duration prolongation.
Subjects receiving CRT with bi-ventricular pacing on prior RV pacing seemed to have the greatest reduction in their mean QRS duration within 24 hours of receiving CRT of all subgroups studied; among subjects receiving de novo CRT, those with pre-existing atrial fibrillation/flutter seemed to have a greater reduction in their mean QRS duration compared with those that did not. The study also showed a greater reduction in the QRS duration with CRT for younger patients—thereby indicating a possibility of greater benefit with early institution of CRT therapy in appropriate cases. Larger studies with more power are needed before the findings can be applied generally.