Cardiac Resynchronization Therapy for Pediatric Patients With Heart Failure and Congenital Heart Disease

Cardiac resynchronization therapy (CRT) is an effective treatment for adult patients with left ventricular (LV) failure. Large prospective, randomized, controlled trials have demonstrated that CRT results in improvement in cardiac function, LV reverse remodeling, decreased hospitalizations for heart failure (HF), improved quality of life, and decreased overall mortality.1–5 However, 30% of adult patients are nonresponders to CRT, spurring further evaluation of electromechanical dyssynchrony to determine optimal pacing sites and to improve CRT selection criteria for maximal response.1,6The positive response in adult HF prompted exploration of the use of CRT in pediatric HF patients. However, the effectiveness of CRT in the pediatric population is difficult to evaluate because of the complex anatomic substrates of congenital heart disease (CHD) and scar formation from multiple cardiac surgeries with a higher proportion of right bundle-branch block (RBBB) and right ventricular (RV) failure than in the adult population. The typical adult HF scenario of an LV ejection fraction (EF) ≤35% with a left bundle-branch block (LBBB) is uncommon in children; therefore, the adult selection criteria for CRT cannot be easily translated to pediatric patients. Furthermore, a small heterogeneous pediatric patient population hinders a systematic assessment of long-term benefit from CRT.In the normal heart, ventricular electrical activation spreads through the His-Purkinje system, which has unique rapid propagation properties and widespread distribution. This allows highly coordinated electrical activation between distant regions of both ventricles, resulting in highly synchronous mechanical contraction. Given the strong relationship between electrical excitation and mechanical contraction in the myocardium, it is not surprising that abnormal electrical activation results in abnormal mechanical contraction.7,8 During a spontaneous or pacing-induced bundle-branch block, ventricular activation spreads primarily cell to cell through the surrounding myocardium, which can be up to 4 times slower than the specialized His-Purkinje …