Relationship between myocardial metabolites and contractile abnormalities during graded regional ischemia. Phosphorus-31 nuclear magnetic resonance studies of porcine myocardium in vivo.
The mechanisms responsible for changes in myocardial contractility during regional ischemia are unknown. Since changes in high-energy phosphates during ischemia are sensitive to reductions in myocardial blood flow, it was hypothesized that myocardial function under steady-state conditions of graded regional ischemia is closely related to changes in myocardial high-energy phosphates. Therefore, phosphorus-31 nuclear magnetic resonance spectroscopy was employed in an in vivo porcine model of graded coronary stenosis. Simultaneous measurements of regional subendocardial blood flow, high-energy phosphates, pH, and myocardial segment shortening were made during various degrees of regional ischemia in which subendocardial blood flow was reduced by 16-94%. During mild reductions in myocardial blood flow (subendocardial blood flow = 83% of nonischemic myocardium), only the ratio of phosphocreatine to inorganic phosphate (PCr/Pi), Pi, and [H+] were significantly changed from control. PCr, ATP, and PCr/ATP were not significantly reduced from control with mild reductions in blood flow. Changes in myocardial segment shortening were most closely associated with changes in PCr/Pi (r = 0.94). Pi and [H+] were negatively correlated with segment shortening (r = -0.64 and -0.58, respectively) and increased over twofold when blood flow was reduced by 62%. Thus, these data demonstrate that PCr/Pi is sensitive to reductions in myocardial blood flow and closely correlates with changes in myocardial function. These data are also consistent with a role for Pi or H+ as inhibitors of myocardial contractility during ischemia.
Schaefer
S
S
Magnetic Resonance Unit, Veterans Administration Medical Center, San Francisco, California 94121.
Schwartz
G G
GG
Gober
J R
JR
Wong
A K
AK
Camacho
S A
SA
Massie
B
B
Weiner
M W
MW
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003326:Coronary Circulation; D003327:Coronary Disease / Q000378:metabolism* / Q000503:physiopathology; D004734:Energy Metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism; D013552:Swine
D010725:Phosphocreatine; D000255:Adenosine Triphosphate