Cardiac responses to β-adrenergic stimulation in anesthetized dogs with chronic congestive heart failure

The cardiac responses to i. v. bolus injections of norepinephrine (NE, 5 and 10 μg) and isoproterenol (ISO, 2 and 5 μg) were compared in dogs with and without chronic congestive heart failure (CHF) induced by construction of a large infrarenal aortacaval fistula. Prior to establishing the shunt there was a significant increase in left ventricular pressure (LVSP), dp/dt_max cardiac output (CO) and stroke volume (SV) to both doses of NE. Pre-shunt there was a significant increase, in dp/dt_max, heart rate (HR), CO and SV to both doses of ISO. Following establishment of the shunt and CHF, there was a significantly depressed response of LVSP and dp/dt_max to both doses of NE compared to pre-shunt changes. Following the shunt and CHF, the response of LVSP was significantly greater at the 2 μg dose of ISO while there was a depressed response of dp/dt_max at both, doses of ISO and a depressed chronotropic response of ISO at both doses. In eight dogs with ligated A-V fistulas and a return of hemodynamic variables as well as heart size to pre-shunt level, there was a reversal of inotropic and chronotropic response to ISO while the inotropic responses to NE were more variable and appeared to remain depressed. In a group of seven normal dogs which were volume expanded with isotonic, isooncotic dextran to similar levels of end diastolic pressures as the CHF dogs, the responses to ISO were not depressed. NE responses were not tested in this group. It is concluded that dogs with chronic volume overload heart failure have a reduced capacity to respond to exogenous catecholamines and that this phenomenon is not related to the volume expanded state of these animals.