Hemodynamic and intracavitary ECG changes with isoproterenol infusion in dogs with normal and hypertrophied right ventricles

Isoproterenol (I) was infused at 0.1 mcg/kg/min into dogs with normal (N) and hypertrophied (RVH) right ventricles to examine differences in coronary and electrographic responses. The pulmonary artery (PA) was banded to a mean proximal PA pressure of 30 mm Hg in 9 dogs and maintained for 6 mth. Mean RV weights in N was 24 gms and in RVH 51 gms. RV and aortic pressures, coronary flow (radioactive microspheres) and RV intracavitary electrograms were measured. Response to I differed (p < 0.5 between N and RVH groups in the following parameters: heart rate, up 43 beats/min in N vs 86 in RVH, RV systolic pressure up 6 mm Hg in N vs 44 in RVH, RV end diastolic pressure down .3 mm Hg in N vs up 2.4 mm Hg in RVH. RV myocardial flow (ml/min/100 g) with I increased from 58 to 86 in N (p < .05) and from 93 to 159 in RVH (p < .05). In N dogs RV coronary vascular resistance (mm Hg/sec/100 g/min) fell from 204 to 133, and in RVH dogs from 121 to 33. Therefore I stimulation increased hemodynamic factors affecting myocardial oxygen needs to a greater extent in dogs with RVH whose coronary vessels were more fully dilated at rest. On the RV electrograms T wave inversion with I increased more than 1 mv in 6/9 dogs with RVH but in none of N. The T wave changes suggest ischemia occurred in some animals with RVH. Recording of RV electrograms during I stimulation may be useful in detecting altered coronary hemodynamics in hypertrophied right ventricles.