MYOCARDIAL EFFECTS OF REPETITIVE EPISODES OF RAPID VENTRICULAR PACINGIN CONSCIOUS DOGS - SURGICAL CREATION, ECHOCARDIOGRAPHIC EVALUATION, AND MORPHOMETRIC ANALYSIS

The interactions of the systemic and myocardial adaptations during and after rapid ventricular pacing, a model of heart failure, were assess ed in conscious, unstressed dogs; Ultrasonic probes and vascular cathe ters were surgically implanted into dogs for measurements of blood flo ws and pressures during 3 weeks of pacing and after 2 months of recove ry. Three weeks of tachycardia (260 beats/min) resulted in a marked re duction in hemodynamic parameters and left ventricular dilatation, wit h caudal wall thinning throughout the pacing period and 1 week of reco very. Sinus rhythm resumed after the pacer was turned off, with return toward normal in hemodynamic parameters; however, left ventricular di latation and ventricular remodeling with significant fibrosis, loss of myocytes, and hypertrophy of the surviving cells were still present a fter 2 months of recovery. In conclusion, even though hemodynamic para meters normalized during recovery, adaptive myocardial remodeling caus ed permanent ventricular fibrosis, hypertrophy, and increased cardiac filling pressures.