Myocardial oxidative metabolism in stunned myocardium after reperfusion therapy in acute coronary syndrome

Objectives Myocardial stunning has been observed after reperfusion therapy in acute coronary syndrome (ACS). However, the mechanisms and myocardial metabolism of stunned myocardium have not been fully studied especially in subacute phase. A clearance rate of 11C acetate reflects myocardial oxygen consumption as oxidative metabolism. We aimed to clarify the oxidative metabolism in stunned myocardium by 11C acetate PET.

Methods 17 patients (mean age 68.0±9.0 y) with acute coronary syndrome (ACS) after reperfusion underwent echocardiography, rest 99mTc sestamibi SPECT and rest 11C acetate PET within 2 weeks after ACS (8.1±2.6 days). Regional wall motion was estimated by 5-point scoring system (1; normal, 5: dyskinesis). Reperfused myocardium was divided into 3 categories such as normal, stunned (normal perfusion but reduced wall motion), and scar (reduced perfusion and wall motion). Oxidative metabolism was measured by the mono-exponential fit of the 11C acetate time-activity curve (kmono) and relative regional kmono was estimated.

Results Among reperfused myocardium, both stunned (n=36) and scar (n=16) segments showed reduced regional wall motion compared to normal (n=37) (2.3±0.6, 2.7±0.9 vs 1.0±0, P<0.05). Both kmono and relative kmono was lower in stunned myocardium (0.042±0.01/min and 67.7±14.7%) than normal (0.051±0.009/min and 82.5±9.3%, p<0.05 each). Such reduction was similar with those in scar segments (0.039±0.01/min, ns, 58.9±18.2%, P<0.05 vs. normal). There was no significant difference in both index between stunned and scar segments.

Conclusions Stunned myocardium showed reduced oxidative metabolism similarly with those of scar tissue. In stunned myocardium, myocardial oxidative metabolism depended on regional function rather than perfusion. This may indicate cardiac protective effect after ischemic injury