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Left ventricular mechanics and geometry in patients with congenital complete atrioventricular block
N J Kertesz1, R A Friedman, S D Colan
1Texas Children's Hospital, and the Department of Pediatrics, Baylor College of Medicine, Houston, USA.
Insights
Congenital complete atrioventricular block (CCAVB) often causes enlarged left ventricles (LV) with normal geometry and enhanced function in children and young adults. Pacemaker implantation did not alter LV function but was associated with increased LV volume and mass.
Area of Science:
- Cardiology
- Pediatric Cardiology
- Congenital Heart Disease
Background:
- Congenital complete atrioventricular block (CCAVB) is frequently associated with cardiomegaly.
- Previous speculation suggested left ventricular (LV) remodeling and increased stroke volume compensate for bradycardia.
- Detailed examination of LV dimensions, geometry, wall stress, and function in CCAVB has been lacking.
Purpose of the Study:
- To investigate the effects of slow heart rate and atrioventricular asynchrony on LV dimensions, geometry, wall stress, and function in pediatric patients with CCAVB.
- To compare LV characteristics in patients with CCAVB to normal controls.
- To assess the impact of pacemaker implantation on LV function and dimensions.
Main Methods:
- Cross-sectional study of 30 patients with CCAVB (age range, 0.2-20 years) across two institutions.
- Echocardiography and 12-lead ECG, including 24-hour ECG recordings, were utilized.
- Comparison with normal control subjects and analysis of regression over age were performed.
Main Results:
- Patients with CCAVB exhibited significantly increased LV volume (Z=1.5+/-1.3) and LV mass (Z=1.2+/-1.5) compared to controls, with normal LV mass-to-volume ratio and geometry.
- LV end-systolic stress was normal (Z=0.2+/-2.3), while shortening fraction (Z=3+/-2.9) and velocity of circumferential fiber shortening (VCF) (Z=3+/-3.1) were increased.
- Patients who underwent pacemaker implantation showed increased LV volume (Z=1.8+/-1.4) and mass (Z=1.7+/-1.2) compared to unpaced patients, but similar LV function.
Conclusions:
- The left ventricle in most CCAVB patients is enlarged with normal geometry and enhanced systolic function during the first two decades of life.
- LV dilation and enhanced function showed no significant age-related changes.
- Pacemaker implantation in CCAVB patients did not affect LV function but was linked to increased LV end-diastolic volume and mass, suggesting a slightly increased load.
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 not 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.