Acute effect of rapid ventricular pacing and volume loading on total vascular capacitance.
OBJECTIVE
Rapid right ventricular pacing (RRVP) at 250 beats/min plus a saline volume load produces acute heart failure manifested by a limited increase in cardiac output in response to the volume load and increased right atrial, pulmonary artery and capillary wedge pressures. The effects on vascular capacitance are unknown.


METHODS
Three groups of six anesthetized splenectomized dogs were subjected to RRVP alone at 250 beats/min for 40 mins volume loading alone with intravenous 0.9% sodium chloride 40 mL/kg over 10 mins or volume loading followed by RRVP for 15 mins. Vascular capacitance, unstressed volume and compliance were determined from pressure-volume curves using transient circulatory arrests induced by acetylcholine before and 40 mins after starting the interventions.


RESULTS
Neither RRVP nor volume loading alone produced acute heart failure or altered total vascular compliance. Fifteen minutes of RRVP after the volume load induced heart failure, reduced compliance (3.4 +/- 0.5 to 2.5 +/- 0.3 mL/mmHg/kg, P < 0.05), increased central blood volume (7.7 +/- 0.7 to 10.6 +/- 0.5 mL/kg, P < 0.01) and reduced the unstressed vascular volume to 57 +/- 10 mL/kg, compared with 77 +/- 9 mL/kg (P < 0.01) after the volume load alone. Stressed blood volume was increased similarly with either volume loading alone (20.1 +/- 2.0 to 30.0 +/- 1.7 mL/kg, P < 0.01) or volume loading plus RRVP (23.5 +/- 3.8 to 30.2 +/- 4.9 mL/kg, P < 0.01). The reduction in unstressed volume rather than an increase in stressed volume was the major peripheral change associated with acute heart failure induced by volume loading plus RRVP.


CONCLUSIONS
RRVP reduced vascular capacitance by a reduction in unstressed volume. Acute volume loading of this smaller vascular compartment resulted in redistribution centrally and acute heart failure.
Ogilvie
R I
RI
Clinical Pharmacology Service, Toronto Hospital, Ontario.
Zborowska-Sluis
D
D
D000818:Animals; D001794:Blood Pressure; D001810:Blood Volume / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology; D002303:Cardiac Output, Low / Q000503:physiopathology*; D002304:Cardiac Pacing, Artificial; D004285:Dogs; D006321:Heart / Q000502:physiology*; D011651:Pulmonary Artery / Q000502:physiology; D016276:Ventricular Function