Background: Inappropriate heart rate response to exercise - chronotropic incompetence - and exercise intolerance are common in patients with a systemic right ventricle. We aimed to assess the relationship between heart rate increase, oxygen consumption, and timing of the right ventricular cardiac cycle in this cohort.
Methods: We prospectively studied nine patients with systemic right ventricles and pre-existing pacemakers using Doppler-echocardiography and treadmill exercise testing. Echocardiography was performed at increasing heart rates. Exercise tests were performed with baseline pacemaker settings and with optimised heart rate response in random order. In addition, eight age- and gender-matched controls underwent exercise testing using a similar exercise protocol.
Results: Patients with a systemic right ventricle had significantly lower peak oxygen consumption compared to controls - 12.6 plus or minus 6.8 versus 31.4 plus or minus 6.6 metres per kilogram per minute (p = 0.0006) - at baseline and active pacemaker reprogramming failed to increase peak oxygen consumption in this cohort - 12.6 plus or minus 6.8 versus 12.4 plus or minus 4.9 millilitres per kilogram per minute (p = NS) at baseline and with reprogramming, respectively. We found not only a marked increase in total isovolumic time but also a significant reduction in total filling time and the aortic velocity time integral, p-value is less than 0.001 for all, at higher heart rates compared to baseline conditions.
Conclusion: This study suggests that despite chronotropic incompetence at baseline, rate-responsive pacing does not improve exercise capacity in patients with a systemic right ventricle. It further indicates that high heart rates may be detrimental in these patients by reducing diastolic filling and stroke volume. These findings may have clinical implications when considering implantation of a permanent pacemaker in this cohort.