Purpose: Optimal atrioventricular delay (AVD) setting for cardiac resynchronisation therapy, i.e. biventricular pacing in patients with heart failure, remains a formidable challenge. Thus, the purpose of this study was to evaluate the effects of different AVD on inter- and intra-ventricular resynchronisation using phase histograms of radionuclide ventriculography (RNV).
Methods: In 17 consecutive patients (mean age 64 +/- 6 years), RNV was performed 236 +/- 350 days after pacemaker implantation for cardiac resynchronisation therapy. Images were acquired during atrial pacing at 80 bpm and during biventricular pacing with AVD ranging from 80 to 160 ms. Inter-ventricular dyssynchrony was measured by the delay between the mean phase angles of the left and right ventricles. Intra-ventricular dyssynchrony was measured by the standard deviation (SD) of left ventricular phase histograms.
Results: Left ventricular (LV) ejection fraction (EF) was inversely correlated to LV dyssynchrony (SD of LV phase histogram, R = -0.82, p < 0.0001). However, the increase in LVEF by biventricular pacing (mean +4.4 +/- 4%) showed only modest correlation to the resulting resynchronisation effect (characterised by a -13 +/- 8 degrees decrease in LV phase histogram SD, R = -0.38, p < 0.0001).
Conclusion: RNV is helpful in optimising pacing parameters for resynchronisation therapy. Varying AVD did not have a major impact on intra- or inter-ventricular resynchronisation. Thus, the benefit of AVD-based LVEF optimisation seems to result from atrioventricular resynchronisation.