Radiographic, Echocardiographic, and Neurohormonal Effects of VVI Pacing in Dogs with Third Degree Atrioventricular Block
Artificial pacemaker (AP) implantation is the mainstay of therapy for treatment of third degree atrioventricular block (3 AVB). Despite several reports detailing long-term survival for dogs with APs there is little data detailing the radiographic, echocardiographic or neurohormonal consequences in this patient population.
Complete baseline (3 AVB) and 4 weeks post fixed rate (100) ventricular demand (VVI) pacing were available for comparison from 9 dogs previously enrolled in a study of physiologic pacing. Compared to 3 AVB, VVI pacing reduced radiographic heart size (12.25+/-2.0 vs 10.92+/-1.1, p=0.01) and pulmonary parenchymal score (median 1, range 0-3 vs median 0, range 0-1, p<0.05). Echocardiographically determined left atrial size (3.21+/-0.5 vs 2.77+/-0.3 cm, p<0.01), left atrial to aorta ratio (1.50+/-0.4 vs 1.28+/-0.3, p=0.02), left ventricular (LV) diastolic dimension (4.41+/-0.6 vs 3.81+/-0.5 cm, p<0.001), fractional shortening (43.6+/-8 vs 22.2+/-7%, p<0.001), and LV posterior wall systolic dimension (1.56+/-0.2 vs 1.36+/-0.2 cm, p=0.03) were reduced during VVI pacing. LV systolic dimension (2.46+/-0.4 vs 3.00+/-0.5 cm, p<0.01) was significantly larger during VVI. Serum aldosterone levels were significantly lower during VVI pacing (158+/-127 vs 49+/-31 pg/ml, p=0.04). There were no significant differences between 3 AVB and VVI pacing in aortic dimension, interventricular septal dimensions, LV posterior wall diastolic dimension, NT-pro atrial natriuretic peptide, brain natriuretic peptide, plasma renin activity, endothelin-1, epinephrine or norepinephrine concentrations. These results suggest compared to 3 AVB, fixed rate VVI pacing at 100 beats per minute reduces radiographic and echocardiographic cardiac dimensions.