Systolic and Diastolic Dysfunction During Atrial Pacing in Conscious Dogs With Left Ventricular Hypertrophy

To determine the extent to which the hypertrophied left ventricle responds to the chronotropic stress induced by graded atrial pacing rates, we studied conscious, chronically instrumented dogs with severe compensated pressure overload left ventricular (LV) hypertrophy induced by aortic banding in puppies 8–10 weeks of age. At 1–2 years, dogs with severe LV hypertrophy (LV free wall/body wt ratio 6.8 ±0.6 g/kg) and sham-operated littermates (LV free wall/body wt ratio 4.0 ±0.3 g/kg) were instrumented with ultrasonic dimension crystals to measure LV short axis internal diameter and wall thickness, miniature LV pressure transducers, and aortic and LV catheters. During atrial pacing (240 beats/min) in eight control dogs, LV pressure did not change from 119 ±2 mm Hg, and mean velocity of circumferential fiber shortening (VCF) did not change from 1.25 ±0.09/sec. In seven dogs with LV hypertrophy, atrial pacing (240 beats/min) decreased systolic LV function; that is, LV systolic pressure decreased (p