Left ventricular mechanics and geometry in patients with congenital complete atrioventricular block

Background Radiographic evidence of cardiomegaly is common in patients with congenital complete atrioventricular block (CCAVB). It has been speculated that left ventricular (LV) remodeling and increased stroke volume counteract the bradycardia, but the effects of slow heart rate and atrioventricular asynchrony on LV dimensions, geometry, wall stress, and function have not been examined in detail. Methods and Results Thirty patients with CCAVB without associated congenital heart disease (mean age, 8.5 +/- 5.3 years; range, 0.2 to 20 years) were included in a cross-sectional two-institution study. Thirty-five echocardiograms were performed using standard techniques. ECG and 24-hour ECG recordings were reviewed. Seven patients did not receive a pacemaker. whereas 23 patients underwent pacemaker implantation after the echocardiogram. Compared with normal control subjects, LV volume (Z score = 1.5 +/- 1.3) and LV mass (Z = 1.2 +/- 1.5) were significantly increased, whereas LV mass-to-volume ratio (1.1 +/- 0.3) and geometry (short-axis diameter/length ratio = 0.65 +/- 0.09) were normal. LV end-systolic stress (ESS) (a measure of afterload) was normal (Z score = 0.2 +/- 2.3), whereas shortening fraction (Z = 3 +/- 2.9) and velocity of circumferential fiber shortening (VCF) (Z = 3 +/- 3.1) were increased. The relationship between VCF and ESS (a preload-insensitive and afterload-adjusted index of contractility) was increased (Z = 2.2 +/- 2) with only small increase in preload (Z = 1.02 +/- 1.1). Regression analyses showed no significant change over age in LV mass, volume, geometry, loading conditions, or systolic function. Patients who ultimately met criteria for pacemaker implantation did nut differ from those who did not in terms of heart rate or LV function but did have increased LV volume (Z score = 1.8 +/- 1.4 versus 0.4 +/- 0.9, P = .03) and LV mass (Z score = 1.7 +/- 1.2 versus 0.2 +/- 1.7, P = .001) compared to the unpaced group. Conclusions In most patients with CCAVB, the LV was enlarged with normal geometry and enhanced systolic function during the first two decades of life. The degree of LV dilation and enhanced function did not significantly change with age. In patients who ultimately underwent pacemaker implantation LV function did not differ from those who remained unpaced, but evidence of a slightly increased load manifested as increased end-diastolic volume and mass.