Cardiac resynchronization therapy (CRT) using biventricular pacing has been proven to be effective in adult patients with left ventricular (LV) systolic dysfunction and QRS prolongation. In this group of patients, CRT improves exercise tolerance, symptoms of heart failure and all-cause mortality.1 In addition, there is growing evidence that inter- and intra-ventricular dyssynchrony induced by conventional right ventricular (RV) apical pacing has deleterious effects on LV function.2-4
CRT in children and patients with congenital heart disease (CHD) could be a very useful therapy for heart failure, but data to support this are still limited.To date, CRT studies in children have all been performed retrospectively and are mostly case reports and small case series.5-11 Only one large study was reported by Dubin et al. retrospectively evaluating the outcome of 103 CRT patients from 22 different institutions.12 Randomized clinical trials are still lacking because the group of patients is relatively small and heterogeneous. The diversity of the CHD population makes it difficult to automatically extrapolate the results from the large randomized CRT trials in adults. For example, in CHD, right bundle branch block and RV failure is a more common problem than LV failure and left bundle branch block (LBBB). Furthermore, the CHD population also includes patients with failing systemic right ventricles and different types of univentricular hearts. These different issues of CRT in CHD will be reviewed.
LV Dysfunction and CRT
The child or CHD patient with LV dysfunction and QRS prolongation appears to bear a resemblance with the typical adult CRT patient. This group consists of CHD patients with LV failure after congenital heart surgery, children with cardiomyopathies, and dilated cardiomyopathy (DCM) following conventional RV pacing. The first two pediatric case reports demonstrated the longer-term benefits of CRT in CHD children with LV failure. These reports describe the outcome of epicardial CRT in an infant with a left sided obstructive lesion and endocardial CRT in a six-year-old boy with multiple ventricular septal defects (VSDs) and mitral valve replacement. In both children symptoms of heart failure improved and LV ejection fractions (EFs) increased.
In the multicenter study by Dubin et al. of 103 patients, the mean age of the study group was 12.8 years (three months to 55.4 years) and the median duration of follow-up was four months. After CRT the EF significantly increased from 26. 2 ┬▒ 11.6% to 39.9 ┬▒ 14.8%. CRT was instituted for systemic LV failure in more than 50% of the study population. Sixteen patients had cardiomyopathy, 14 had congenital heart block and 30-40 were CHD patients, including patients with left-sided obstructive lesion and atrioventricular canal defects. In this study no statistical significant differences were found between the different sub-groups.
Case reports and case series have reported even more striking improvement of LV function and reverse LV remodeling in the group of children with congenital heart block and DCM that underwent upgrading of RV pacing to biventricular pacing.13-14 In a recent study of six children with congenital heart block LVEF improved from 34┬▒ 6-60 ┬▒ 2% and LV diastolic dimension shortened from 55 ± 8-43 ± 5mm after CRT.14
Systemic RV Dysfunction and CRT
The RV is the systemic ventricle in congenitally corrected transposition of the great arteries (cCTGA or L-TGA) and in complete transposition of the great arteries (D-TGA) after an intra-atrial baffle operation (Mustard or Senning procedure). Ventricular dyssynchrony is often present as a result of conventional pacemaker therapy or intrinsic conduction delay after surgery.A large proportion of these patients will eventually develop heart failure as result of systemic RV dysfunction and mortality is very high for symptomatic patients.15
The first successful report of endocardial CRT for systemic RV dysfunction was in a 24-old patient with congenitally corrected transposition of the great arteries (cCTGA) with severe heart failure and RV dysfunction long-term after a Rastelli operation. Later, Janousek et al. reported the hemodynamic benefits of CRT in a group of eight patients with systemic RV, in two of them CRT was instituted as a preventive measure. Average RV ejection fraction measured with radionuclide ventriculography increased by 10%; however, no decrease in tricuspid regurgitation was observed.The multicenter study of Dubin et al. also included 13 cCTGA patients and four D-TGA patients after the Mustard or Senning procedure. Thirteen of the 17 patients had clinical improvement and RV ejection fraction improved by 13.3 ± 11.3%. CRT appears to be a promising therapy in patients with systemic RVs and should even be considered as preventive therapy in this high-risk group.
Single Ventricular Dysfunction and CRT
In CHD the term 'single ventricle' is used when one ventricle is absent or hypoplastic, excluding a biventricular repair. The functional ventricle can have either a LV or RV morphology or can be of an indeterminate type. The final surgical step in patients with single ventricle physiology is the Fontan operation or total cavopulmonary connection. Unfortunately, the prognosis of Fontan patients is still worrying and a high percentage of patients will develop heart failure and death during long-term follow-up.15
CRT by means of multisite pacing has been performed in 26 patients in the acute postoperative phase, including stage I Norwood procedures, Fontan and Glenn procedures.16 Multisite pacing from the outflow tract and lateral or anterior wall improved intraventricular synchrony and increased cardiac index and systolic blood pressure. Permanent CRT was successful in an unoperated 18-year-old patient with a univentricular heart, common AV valve and pulmonary stenosis with heart failure and cyanosis.9 Epicardial multisite pacing was assessed with the ventricular leads positioned on the right and left sides of the single ventricle. In this patient New York Heart Association (NYHA) Classification improved from class IV to II and EF increased from 20-45%.
In the multicenter study of Dubin et al. seven children with univentricular heart underwent CRT.12 In this group no improvement of ejection fraction was noted and only two of seven patients showed clinical improvement. Further studies are needed to evaluate the value of CRT and the optimal pacing sites in this heterogeneous group of patients.
RV Dysfunction and CRT
RV (pulmonary) dysfunction is a common cause of heart failure in CHD and is often associated with complete right-BBB. Many types of congenital heart defects develop long-term RV dysfunction and RV dilatation, due to a combination of pulmonary or tricuspid regurgitation, surgical scars and pressure overload. Several studies have properly demonstrated that RV resynchronization by multisite pacing or RV pacing alone improved hemodynamics in children with acute heart failure after congenital heart surgery in the post-operative period.17-19
RV resynchronization by RV pacing was also studied acutely in seven patients with chronic RV failure after repair of tetralogy of Fallot and after the Ross procedure.20 In this study, atrioventricular pacing in patients with RBBB and RV dysfunction improved cardiac index and RV dP/dt. Unfortunately, there was no relationship between the site that produced the narrowest QRS duration and the site that produced the best dP/dt.
So far, no literature data exist on the use of permanent CRT in CHD patients with chronic RV failure and RBBB. Future studies are necessary to clarify the possible role of CRT in the management of chronic RV failure in CHD.
The use of CRT in children and adult with CHD is still a new treatment modality and its use has only just started. It is a challenging therapeutic area in CHD but more data are essential to select good candidates and to avoid overuse or underuse in this group. Well-designed prospective multicenter studies are needed. Detailed information of the degree of ventricular dyssynchrony should be obtained with the use of two-dimensional (2-D) and 3-D echocardiography and tissue Doppler imaging.11 These studies should evaluate the relationship between ventricular dysfunction, mechanical dyssynchrony and the effectiveness of CRT in the different sub-groups of children and adults with CHD.