Objective: We sought to determine the effect of temporary interruption of long-term right ventricular (RV) pacing on left ventricular (LV) function and mechanical dyssynchrony in children and young adults with complete heart block.
Methods: Twelve patients aged 20.0±7.4 years with congenital heart block (group I) and six aged 22.7±11.0 years with surgically acquired heart block (group II) with RV pacing were studied. The pacing rate was reduced to less than patient’s intrinsic heart rate and maintained for 5 minutes. The LV ejection fraction (EF) and systolic dyssynchrony index (SDI) as determined by three-dimensional echocardiography, two-dimensional global LV systolic strain and strain rate (SR), and Doppler-derived isovolumic acceleration (IVA) before and after interruption of RV pacing were compared.
Results: The LV EF, strain, SR, and IVA increased and QRS duration decreased significantly after pacing interruption in both groups (all p<0.05). While SDI decreased significantly in both groups I (6.78±2.30 to 3.79±0.83, p<0.001) and II (9.17±4.08 to 5.03±1.64, p=0.001), it remained higher in group II than in group I (p=0.046) after pacing interruption. The prevalence of LV dyssynchrony (SDI>4.7%) decreased significantly in group I (83.3% to 25.0%, p=0.006) but not group II (66.7% to 50.0%, p=0.50). The percent increase in LV ejection fraction correlated positively with percent reduction in LV SDI (r=0.80, p<0.001).
Conclusions: Achievement of LV synchronization after interruption of RV pacing occurs more commonly in patients with congenital than those with surgically acquired heart block, which has implications on the benefit of cardiac resynchronization therapy.