A Single Center, Prospective, Pilot Study Examining the Evaluation of Exercise Capacity in Chronically RV Paced Children and Young Adults

In third degree, or complete atrioventricular (AV) block, atrial electrical impulses fail to conduct to the ventricles. Congenital complete AV block (CCAVB) has an incidence of 1 in 15,000 to 1 in 25,000 live births and has a strong association with maternal antibodies. Patients with isolated CCAVB range from completely asymptomatic to experiencing syncope, exercise intolerance or congestive heart failure. A portion of the symptoms attributable to CCAVB are secondary to the inability to increase heart rate, and hence cardiac output, in response to varying physiologic demands. For symptomatic patients, the mainstay of therapy has been cardiac pacing. Dual chamber pacing, with atrial sensing and ventricular pacing, allows for restoration of physiologic heart rates and response to exercise or increased metabolic demands. Resumption of AV synchrony allows for more efficient ventricular filling. Overall, pacing in patients with CCAVB would be expected to result in improved cardiac function and exercise tolerance.

The traditional ventricular site for pacing in patients with CCAVB has been the right ventricular apex (RVA). This results in interventricular dyssynchrony as pacing first stimulates the right ventricle, rather than the typical midline ventricular activation pattern seen in patients with intact AV node conduction. Mounting evidence shows that long term RV pacing results in morphologic changes to the LV with resultant compromised performance. Further studies have shown that chronic RV pacing diminishes exercise capacity in patients with heart failure as well as asymptomatic adults. There have been studies, by our group in particular, that have documented ventricular changes in the paced pediatric patient. No published study has examined the possible deleterious effects of RV pacing on exercise capacity in children. We, therefore, propose to do a detailed evaluation of exercise performance, as measured by exercise duration, maximal heart rate, oxygen uptake and ventilatory response, in asymptomatic chronically RV paced children and young adults.

Specific Aim 1: To describe the effects of dyssynchronous ventricular activation on exercise performance in children requiring long term RV pacing

Hypothesis 1: Long term dyssynchronous electromechanical activation, secondary to right ventricular apical pacing, has deleterious effects on the exercise capacity of asymptomatic pediatric patients.

Specific Aim 2: To correlate changes in exercise performance with tissue Doppler indices of mechanical dyssynchrony.