Specialized Pacing for Patients With Congenital Heart Disease

Sinus node dysfunction is highly prevalent among patients with congenital heart disease, manifesting as resting bradycardia or chronotropic incompetence. As children and adults with congenital heart disease are now expected to have increasing life-expectancy; with well over 1 million adult patients currently living in North America,1 issues such as mental health, acquired comorbidities and their impact on overall cardiovascular health have assumed increased scrutiny. It is now understood that objective measures of aerobic capacity, such as peak VO2, peak VE/VCO2, and heart rate reserve predict all-cause mortality for adult patients with congenital heart disease. As the chronotropic response during exercise is a key determinant of aerobic capacity, improvement in sensor-based technology for heart rate support is expected to have a significant impact on functional capacity and longevity in this population. Some forms of congenital heart disease, such as single ventricle physiology after the Fontan population are especially likely to benefit, as cardiac output is determined almost exclusively by heart rate during exertion due to limited ability to augment cardiac stroke volume.2 It is also becoming increasingly clear that sedentary behaviors are highly relevant to overall cardiovascular health in the general adult population. Adult patients with congenital heart disease are at especially high risk for sedentary behavior as a result of 1) chronic restriction for physical activities based on ill-founded medical advice, 2) chronotropic incompetence resulting from prior surgical palliations and hemodynamic stressors, and 3) overestimation of physical activity. 5.0 Enrollment/Randomization Patient Enrollment: The treating physician will identify potential subjects with a previously implanted pacemaker and present a brief overview of the study; if the subject is interested, the study will be described in detail. Informed consent will be obtained by the investigator after discussing the study, including the voluntary nature of participation and notification the subject can withdraw at any time. Ample time for questions and answers will be allowed. The investigator will give the subject and his/her legal guardian the opportunity to take the consent home to think about it more, with the option to call or meet with the investigator to ask additional questions. If the subject and/or his/her parent/legal guardian agree to participate, the investigator will ask them to sign a written, informed consent and assent. A copy of the assent and consent will be given to the subject and/or his/her parent/legal guardian. Randomization Procedure: This will be a single-blind placebo-controlled randomized crossover study with 2 treatments: CLS-on versus CLS-off (accelerometer only). Each enrolled patient will receive both treatments for 3 months. The order of treatments will be randomized 1:1. Randomization There will be a 50:50 randomization, with half the subjects randomized to CLS-on then CLS-off, and half randomized to CLS-off then CLS-on. Subjects previously receiving rate-responsive pacing with CLS that are randomly selected to CLS-on will continue with the identical programmed parameters. For subjects not previously receiving rate-responsive pacing with CLS that are randomly selected to CLS-on nominal programming will be utilized with a base rate of 60 beats per minute. Subjects will then initiate treatment A (CLS-on or CLS-off) in a blinded fashion. At 3 months, subjects will undergo testing. After 3 months of treatment A, subjects will be reprogrammed to treatment B. Tracking of physical activity with the device accelerometer will continue during this period. After 3 months of treatment B, repeat testing will be repeated. Patients will be followed during both treatment phases per usual clinical routine. Patients who experience significant symptoms (extreme fatigue, debilitating palpitations, or other clinically relevant symptoms) will be evaluated by their treating physician. Subjects that have any adverse events during treatment A will discontinue treatment A and immediately crossover to treatment B. Subjects with events during treatment B will be removed from the study and unblinded. Further treatment will be determined by the treating physician.