GADOLINIUM ATTENUATES THE UPWARD SHIFT OF THE LEFT-VENTRICULAR DIASTOLIC PRESSURE-VOLUME RELATION DURING PACING-INDUCED ISCHEMIA IN DOGS

Background The mechanism of the reversible upward shift of the left ventricular diastolic pressure-volume relation during demand ischemia is controversial. To assess the possibility that cation influx through stretch-activation channels may contribute to the upward shift, we asked whether gadolinium, a blocker of the stretch-activated channels, attenuates the upward shift of the diastolic pressure-volume relation during pacing-induced ischemia in 5 dogs. Methods and Results To produce pacing-induced ischemia, we constricted the left anterior descending and circumflex coronary arteries to reduce their flows by approximately 30% and paced the left atrium at 150 to 180 beats per minute for 3 minutes. We measured left ventricular pressure, volume, and two segment lengths with micromanometers, a conductance catheter, and ultrasonic crystals, respectively. We recorded these variables during baseline, coronary stenosis, and pacing-induced ischemia (immediately after rapid pacing). After injecting 20 mg/kg (76 mu mol/kg) gadolinium, we repeated the measurements during coronary stenosis (gadolinium experiment) and pacing-induced ischemia (pacing-induced ischemia plus gadolinium experiment). For each measurement, we recorded the variables in steady state to obtain diastolic pressure-volume and pressure-segment length loops and then during a brief (within 25 seconds) inferior vena caval occlusion to obtain the left ventricular end-diastolic pressure-volume relation. We found that left ventricular diastolic pressure-volume and pressure-segment length loops in steady-state beats shifted upward from coronary stenosis to pacing-induced ischemia. After injection of gadolinium, the upward shift from gadolinium to pacing-induced ischemia plus gadolinium was smaller than the shift from coronary stenosis to pacing-induced ischemia. Similarly, the left ventricular end-diastolic pressure-volume relation obtained during vena caval occlusion shifted upward (by 2.2+/-0.6 [SE] mm Hg) from coronary stenosis to pacing-induced ischemia. After injection of gadolinium, the upward shift from gadolinium to pacing-induced ischemia plus gadolinium was smaller (by -2.1+/-0.4 mm Hg). Conclusions These results indicate that gadolinium, a blocker of stretch-activated channels, attenuates the upward shift of the diastolic pressure-volume relation during pacing-induced, ischemia, suggesting that the cation influx through stretch-activated channels may contribute to this upward shift.