Time to therapy and salvage in myocardial infarction

Objectives. This study sought to examine the influence of time to reperfusion on myocardial salvage. Background. Major trials of reperfusion therapy for myocardial infarction (MI) have demonstrated improved outcome for patients achieving earlier reperfusion. However, some patients experience significant benefit despite delayed reperfusion. Methods. Fifty-five patients with a first anterior MI underwent successful reperfusion therapy (angioplasty or thrombolysis). Technetium-99m (Tc-99m) sestamibi was injected before reperfusion therapy and again at hospital discharge to determine the myocardial salvage index for each patient. Residual flow to the infarct territory was assessed by the nadir of the Tc-99m sestamibi count-profile curve. Results. The salvage index showed wide variability (range -0.04 to 1.0), and extreme values were seen in 34.5% of the group (<0.10 in 9%, >0.90 in 25%). A high salvage index was associated with reperfusion therapy before 2 h (p = 0.02) or good residual blood flow (p < 0.01). For the 10 patients who received reperfusion therapy within 2 h, residual blood flow was not correlated with salvage (p = 0.12). For the 45 patients treated after 2 h, residual blood flow correlated significantly with salvage (r = 0.57, p < 0.0001). There was a significant interaction (p < 0.05) between residual blood flow and time to therapy, indicating that the effect of each variable on salvage depended on the value of the other. Multiple historic and hemodynamic variables were examined, but none demonstrated any association with residual flow or myocardial salvage. Conclusions. In patients with acute MI, successful reperfusion therapy within 2 h is associated with the greatest degree of myocardial salvage. For patients treated after 2 h, residual blood flow to the infarct-related territory appears to be the most important determinant of myocardial salvage.