The hypertrophied left ventricle is at considerably greater risk for injury when subjected to global
ischemia than is an otherwise normal heart. We evaluated the efficacy of
verapamil, a
calcium-channel blocking agent, as an adjunct to standard
crystalloid cardioplegic solution in animals with
left ventricular hypertrophy subjected to
myocardial ischemia during
cardiopulmonary bypass. Infracoronary
aortic stenosis was produced in 15 mongrel puppies by plication of the noncoronary cusp of the aortic valve. Studies were conducted 3 to 4 months later. Left ventricular
catheter-tip
pressure transducers and major and minor axis ultrasonic dimension crystals were inserted, and the animals were then supported by
cardiopulmonary bypass with 30 minutes of normothermic
ischemia. Animals were randomized to receive either standard hyperkalemic
crystalloid cardioplegic solution (n = 8) or the same
solution with
verapamil, 0.1 mg/kg (n = 7). After the 30 minutes of
ischemia, the animals were supported on
cardiopulmonary bypass for an additional 30 minutes and then separated from bypass. They were then studied for another 2 hours by measurement of myocardial
adenosine triphosphate content, myocardial blood flow, systolic function with use of the end-systolic pressure/volume ratio, and compliance with use of the natural strain coefficient of the minor axis at 15 mm Hg end-diastolic pressure. There was a better recovery of systolic function in the animals treated with
verapamil (89.2% versus 63.3%). The compliance as measured with use of the minor axis natural strain coefficient returned essentially to baseline in the group of animals treated with
verapamil (0.236 +/- 0.038 before
ischemia and 0.254 +/- 0.043 2 hours after
ischemia), but it fell markedly in the control animals (0.219 +/- 0.027 before
ischemia and 0.153 +/- 0.016 2 hours after
ischemia). Myocardial
adenosine triphosphate levels were not significantly different at any time during the study. Likewise, myocardial blood flow was not significantly different between groups. We conclude that the addition of
verapamil to hyperkalemic
cardioplegic solution improves recovery of both systolic and diastolic function after global
ischemia in dogs with
left ventricular hypertrophy resulting from
aortic stenosis. The precise mechanism for this is unknown.