Haemodynamic and neurohumoral response in heart failure produced by rapid ventricular pacing

The aim was to determine the exact sequence of hormone changes during the progression of fluid retention in a canine model of "congestive cardiac failure" induced by rapid right ventricular pacing, and during recovery when pacing is stopped.

Rapid ventricular pacing at a rate of 250 pulses.min-1 was used in six mongrel dogs with implanted right ventricular pacemakers. Right heart haemodynamics were measured by means of Swan Ganz catheterisation, allowing flow measurement by thermodilution and pressure measurement by external manometry. Plasma renin activity, arginine vasopressin, and atrial natriuretic factor were assayed on venous blood samples by radioimmunoassay. Noradrenaline was assayed by high pressure liquid chromatography.

The onset of rapid pacing was accompanied by a fall in cardiac output and a rise in pulmonary arterial, pulmonary capillary wedge, and right atrial pressures. Noradrenaline and atrial natriuretic factor rose. Plasma renin activity showed an initial fall followed by a rise, and arginine vasopressin was unchanged in the first 8 h. When rapid pacing was continued for a further 35 d, clinical signs of fluid retention appeared by day 28, by which time cardiac output had fallen, and central pressures risen further. Atrial natriuretic factor peaked at around 14 d whereas plasma renin activity, arginine vasopressin, and noradrenaline tended to reach a plateau at about d 20 and then to show further increases as clinical signs of fluid retention appeared; this was most marked with plasma renin activity. Cessation of pacing at d 35 caused a rapid reversal (increase) of cardiac output but a more gradual reversal (decrease) of right heart pressures over 5 d; only wedge pressure returned to base line. Arginine vasopressin and plasma renin activity fell rapidly to around 40% of the final pacing levels and reached basal values after 8 h and 48 h respectively. Noradrenaline fell after 8 h and reached basal levels in 5 d. Atrial natriuretic factor fell quickly by 60% after 8 h but remained above basal levels for 5 d. At the end of pacing, body weight fell rapidly in conjunction with a large diuresis.

These findings are compatible with a major role of one or more of renin, vasopressin, and noradrenaline in the pathophysiology of the fluid retention of heart failure; the manifestations are not counteracted by the rise in atrial natriuretic factor.