Patients with
aortic stenosis are susceptible to
myocardial ischemia during hemodynamic stress, which may be caused by two mechanisms. First, vascular abnormalities inherent in myocardial
hypertrophy may impair coronary vasodilation, limiting the ability to increase coronary blood flow to meet increased metabolic demands. Second,
aortic stenosis itself may cause an imbalance between
oxygen supply and demand during hemodynamic stress by decreasing aortic pressure (decreasing coronary perfusion or
oxygen supply) and increasing left ventricular pressure (increasing
oxygen demand). By decreasing aortic valve gradient without immediately altering ventricular
hypertrophy, aortic balloon valvuloplasty offers the opportunity to distinguish these mechanisms. We hypothesized that aortic valvuloplasty would improve the balance between myocardial
oxygen supply and demand, especially during
isoproterenol infusion. Nine patients undergoing aortic balloon valvuloplasty were assessed at baseline and during
isoproterenol infusion (5 +/- 2 micrograms/min, mean +/- SD) before and after valvuloplasty. Valvuloplasty increased myocardial
oxygen supply. After valvuloplasty,
isoproterenol decreased diastolic pressure time index (DPTI) less and increased coronary sinus blood flow more than before valvuloplasty (-630 +/- 367 vs. -292 +/- 224 mm Hg.sec/min, p = 0.02 and 53 +/- 137 vs. 179 +/- 145 ml/min, p = 0.001, respectively). Valvuloplasty also decreased
oxygen demand, decreasing systolic pressure time index (SPTI) from 4,135 +/- 511 to 3,021 +/- 492 mm Hg.sec/min (p = 0.0002). Valvuloplasty improved the balance between myocardial
oxygen supply and demand, increasing baseline DPTI:SPTI, decreasing aortocoronary sinus
oxygen content difference (0.51 +/- 0.15 to 0.68 +/- 0.14, p = 0.005 and 96 +/- 14 to 78 +/- 15 ml O2/l, p = 0.002, respectively), and decreasing myocardial
lactate production during
isoproterenol infusion (mean
lactate extraction fraction, -0.26 +/- 0.40 to 0.14 +/- 0.17; p = 0.01). We conclude that aortic valvuloplasty improves the balance between myocardial
oxygen supply and demand during hemodynamic stress induced by
isoproterenol infusion. We speculate that the clinical improvement, which often occurs in these patients after valvuloplasty despite persistence of hemodynamically "critical"
aortic stenosis, is in part attributable to immediate improvement in the myocardial
oxygen supply:demand ratio.