HEMODYNAMIC, RENAL, AND HORMONAL EFFECTS OF RAPID VENTRICULAR PACING IN CONSCIOUS DOGS

The interactions of the systemic adaptations during and after rapid ve ntricular pacing, a model of heart failure, were assessed in conscious , unstressed dogs. One week of ventricular tachycardia (260 beats/min) significantly reduced mean +/- SEM cardiac output (2.3 +/- 0.1 to 1.2 +/- 0.1 liter/min), mean arterial pressure (119 +/- 3 to 93 +/- 3 mm Hg), renal blood flow (168 +/- 19 to 96 +/- 9 ml/min), sodium excretio n (36 +/- 5 to 10 +/- 4 mEq/d), increased left and right atrial pressu res (8 +/- 1 to 21 +/- 1 and 4 +/- 0 to 11 +/- 1 mm Hg, respectively), plasma atrial natriuretic peptide concentration (24 +/- 4 to 141 +/- 38 fmol/ml), plasma cyclic GMP concentration (9 +/- 1 to 16 +/- 4 pmol /ml), and urinary cyclic GMP excretion (0.77 +/- 0.05 to 2.18 +/- 0.34 nmol/min). These changes persisted throughout 3 weeks of pacing. Grad ual increases in systemic and renal vascular resistances (to 122 +/- 1 7 and 1.30 +/- 0.22 mm Hg/liter/min, respectively) and reductions in g lomerular filtration rate (65 +/- 6 to 44 +/- 4 ml/min) reached signif icance during the third week. Resumption of sinus rhythm stimulated a brisk natriuresis and a return of cardiac output, systemic vascular re sistance, and hormone concentrations to control values within 7 days. However, increases of left and right atrial pressures (14 +/- 2 and 8 +/- 1 mm Hg, respectively) were still present after 2 months of recove ry. In conclusion, persistent increases in cardiac filling pressures w ere induced by rapid ventricular pacing in conscious, unstressed dogs, whereas the systemic hemodynamic, renal, and hormonal responses were largely reversible during recovery. These data suggest that this model may be used to sustain a standing colony of conscious dogs with conge stive heart failure.