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Failure of rate responsive ventricular pacing to improve physiological performance in the univentricular heart
P P Karpawich1, S M Paridon, W W Pinsky
1Section of Pediatric Cardiology, Children's Hospital of Michigan, Wayne State University School of Medicine, Detroit 48201.
Insights
Rate-responsive pacing (VVIR) in children after Fontan procedure did not improve exercise capacity. Despite increased heart rate, physiological measures like VO2 and VAT remained unchanged, indicating persistent hemodynamic issues.
Area of Science:
- Pediatric Cardiology
- Cardiac Electrophysiology
- Congenital Heart Disease
Background:
- The Fontan procedure is a palliative surgery for univentricular hearts.
- Symptomatic bradycardia is a concern in post-Fontan patients requiring pacing.
- The efficacy of rate-responsive ventricular pacing (VVIR) in this population is not well-established.
Purpose of the Study:
- To evaluate the physiological efficacy of VVIR pacing compared to fixed-rate pacing (VVI) in children with symptomatic bradycardia post-Fontan procedure.
- To assess the impact of VVIR pacing on exercise capacity and hemodynamic parameters.
Main Methods:
- Six pediatric patients (ages 6-21) post-Fontan procedure with symptomatic bradycardia underwent randomized treadmill exercise testing.
- Comparative testing was performed in fixed-rate (VVI) and rate-responsive (VVIR) pacing modes.
- Physiological parameters including heart rate, blood pressure, VO2, VCO2, RER, and VAT were continuously monitored.
Main Results:
- VVIR pacing resulted in a significant increase in heart rate during exercise (P < 0.01) compared to VVI pacing.
- However, maximum work rate (watts), oxygen consumption (VO2), and ventilatory anaerobic threshold (VAT) showed no significant difference between the two pacing modes.
- These findings suggest that enhanced heart rate response does not translate to improved exercise performance.
Conclusions:
- In children with univentricular hearts following the Fontan procedure, VVIR pacing does not improve physiological efficacy or exercise capacity.
- Altered hemodynamics in these patients may limit the benefits of rate-responsive pacing.
- Further research is needed to optimize pacing strategies in the post-Fontan population.
Abstract:
The physiological efficacy of single chamber, rate responsive ventricular pacing (VVIR) is unknown for symptomatic patients following the Fontan procedure for univentricular hearts. A total of six postoperative children, ages 6-21 years (mean 13), with symptomatic bradycardia requiring pacing therapy, underwent comparative treadmill exercise testing in randomized fixed rate (VVI) and VVIR pacing modes. In all instances, implanted activity pulse generators (Medtronic Model 8403) were programmed to identical age-appropriate low paced rates during VVI and VVIR modes with the upper rate response at 150 ppm. All studies were performed at least 2 weeks apart. Physiological values of heart rate, blood pressure, work rate (watts), oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory exchange ratio (RER) were monitored continuously during each test using a 1 minute incremental treadmill protocol. Ventilatory anaerobic threshold (VAT) was calculated from VO2, VCO2, and minute ventilation. The results demonstrated that although there was a significant increase in paced heart rate per minute throughout exercise (P less than 0.01) with VVIR pacing, maximum watts, VO2, and VAT remained unchanged. These findings indicate that in spite of an improved chronotropic response to exercise, children with univentricular hearts following the Fontan procedure continue to demonstrate altered hemodynamics which negate potential benefits of VVIR pacing.