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 stres s, 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 i n a cross-sectional two-institution study. Thirty-five echocardiograms were performed using standard techniques. ECG and 24-hour ECG recordi ngs 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, where as LV mass-to-volume ratio (1.1 +/- 0.3) and geometry (short-axis diam eter/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), wh ereas shortening fraction (Z = 3 +/- 2.9) and velocity of circumferent ial fiber shortening (VCF) (Z = 3 +/- 3.1) were increased. The relatio nship between VCF and ESS (a preload-insensitive and afterload-adjuste d index of contractility) was increased (Z = 2.2 +/- 2) with only smal l increase in preload (Z = 1.02 +/- 1.1). Regression analyses showed n o significant change over age in LV mass, volume, geometry, loading co nditions, or systolic function. Patients who ultimately met criteria f or pacemaker implantation did nut differ from those who did not in ter ms of heart rate or LV function but did have increased LV volume (Z sc ore = 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 grou p. Conclusions In most patients with CCAVB, the LV was enlarged with n ormal geometry and enhanced systolic function during the first two dec ades of life. The degree of LV dilation and enhanced function did not significantly change with age. In patients who ultimately underwent pa cemaker implantation LV function did not differ from those who remaine d unpaced, but evidence of a slightly increased load manifested as inc reased end-diastolic volume and mass.