Abstract
BACKGROUND: Left ventricular outflow obstruction drives symptoms and outcomes in obstructive hypertrophic cardiomyopathy (oHCM). Right ventricular pacing (RVP) can desynchronize the left ventricle to relieve this and allows control of atrioventricular delay (AVD) but may impair ventricular function. We used high-precision assessment to quantify the hemodynamic and echocardiographic effects of RVP in oHCM. METHODS: Patients with oHCM and implanted dual-chamber pacing devices underwent continuous recording of ECG, beat-by-beat outflow tract continuous wave Doppler, and beat-by-beat, noninvasive finger-cuff blood pressure while pacing was alternated between atrium-only pacing and AV-sequential RVP at a range of AVDs at 5 bpm above resting heart rate and 100 bpm. Changes in systolic blood pressure (∆SBP) and left ventricular outflow tract gradient (∆LVOTg) were fitted to parabolas to produce reproducible, narrow confidence interval estimates of effects. RESULTS: Twenty two patients were recruited (60% male, mean resting LVOTg 53 mmHg). At just above resting heart rate (mean 75 bpm), RVP produced mean peak ∆SBP from AAI to DDD of 2.47 mmHg (95% confidence interval: 0.19-4.76, p = 0.04). The mean AVD for peak ∆SBP was 173.2 ms. Mean LVOTg reduction at this AVD was 8.31 mmHg (2.43-14.18, p < 0.001). Apart from the hemodynamically optimum AVD, no other AVDs produced statistically significant increases in SBP. At 100 bpm, greater increases in SBP and reductions in LVOTg were seen at hemodynamically optimal AVD. CONCLUSION: Multiple alternation assessment allows precise, reproducible, narrow confidence interval quantification of hemodynamic and echocardiographic pacing effects. RVP can reduce LVOTg while preserving or improving cardiac output, but AVD is a key modifier of this relationship.