Use of the 12-lead ECG to detect myocardial reperfusion and salvage during acute myocardial infarction

Paramedic transtelephonic communication to cardiologist of clinical and electrocardiographic assessment for rapid reperfusion of ST-elevation myocardial infarction

BACKGROUND/PURPOSE

We tested the hypothesis that paramedic recognition of ST-elevation myocardial infarction (STEMI) and cardiologist activation of the cardiac catheterization laboratory without transmission of the electrocardiogram reduces door-to-balloon times.

METHODS

We studied a consecutive series of patients suspected to have STEMI who were taken to the cardiac catheterization laboratory in the 6-month period before hotline implementation (historical controls) and during the first year of hotline use (intervention group, hotline; emergency medical service patients without hotline, concurrent controls).

RESULTS

Emergency medical services activated the hotline 47 times, and 25 patients were subsequently taken to the catheterization laboratory. Patients who received PCI involving hotline use (n = 20) had significantly shorter door-to-balloon times (58 minutes; 25th-75th percentile, 52-73 minutes) than historical controls (n = 15) (112 minutes; 25th-75th percentile, 81-137; P < .0001) and concurrent controls (n = 15) (92 minutes; 25th-75th percentile, 76-112; P = .019).

CONCLUSIONS

Paramedic transtelephonic communication to cardiologist of clinical and electrocardiogram assessment resulted in a 54-minute reduction in door-to-balloon time for patients with STEMI.

Electrocardiographic infarct size assessment after thrombolysis: insights from the Acute Myocardial Infarction STudy ADenosine (AMISTAD) trial

BACKGROUND

Noninvasive methods are needed to evaluate reperfusion success in patients with acute myocardial infarction (MI). The AMISTAD trial was analyzed to compare MI size and myocardial salvage determined by electrocardiogram (ECG) with technetium Tc 99m sestamibi single-photon emission computerized tomography (SPECT) imaging.

METHODS

Of 236 patients enrolled in AMISTAD, 166 (70 %) with no ECG confounding factors and no prior MI were included in this analysis. Of these, group 1 (126 patients, 53%) had final infarct size (FIS) available by both ECG and SPECT. Group 2 (56 patients, 24%) had myocardium at risk, FIS, and salvage index (SI) assessed by both SPECT and ECG techniques. Aldrich/Clemmensen scores for myocardium at risk and the Selvester QRS score for final MI size were used. Salvage index was calculated as follows: SI = (myocardium at risk-FIS)/(myocardium at risk).

RESULTS

In group 1, FIS was 15% (6, 24) as measured by ECG and 11% (2, 27) as measured by SPECT. In the adenosine group, FIS was 12% (6, 21) and 11% (2, 22). In the placebo group, FIS was 16.5% (7.5, 24) and 11.5% (3.0, 38.5) by ECG and SPECT, respectively. The overall correlation between SPECT and ECG for FIS was 0.58 (P = .0001): 0.60 in the placebo group (P = .0001) and 0.54 (P = .0001) in the adenosine group. In group 2, myocardium at risk was 23% (17, 30) and 26% (10, 50) with ECG and SPECT, respectively (P = .0066). Final infarct size was 17% (6, 21) and 12% (1, 24) (P < .0001). The SI was 29% (-7, 57) and 46% (15, 79) with ECG and SPECT, respectively (P = .0510).

CONCLUSIONS

The ECG measurement of infarct size has a moderate relationship with SPECT infarct size measurements in the population with available assessments. This ECG algorithm must further be validated on clinical outcomes.

Estimates of myocardium at risk and collateral flow in acute myocardial infarction using electrocardiographic indexes with comparison to radionuclide and angiographic measures

OBJECTIVES

This study sought to determine the accuracy of the initial 12-lead electrocardiogram (ECG) in predicting final infarct size after direct coronary angioplasty for myocardial infarction and to examine which physiologic variables known to be determinants of outcome the ST segment changes most closely reflect.

BACKGROUND

Myocardium at risk, collateral flow and time to reperfusion have been shown to be independent physiologic predictors of infarct size in animal and clinical models. However, such measurements may be difficult to perform on a routine basis in patients with myocardial infarction. The standard 12-lead ECG is inexpensive and readily available.

METHODS

Sixty-seven patients with acute myocardial infarction, ST segment elevation and duration of chest pain < 12 h had an initial injection of technetium-99m sestamibi. Tomographic imaging was performed 1 to 8 h later (after direct coronary angioplasty), and the images were quantified to measure perfusion defect size (myocardium at risk) and severity (a measure of collateral flow). Contrast agent injection and tomographic acquisition were repeated at hospital discharge to measure infarct size. The ST segment elevation score was calculated for each patient according to infarct location and using previously described formulas.

RESULTS

ST segment elevation score correlated closest with the radionuclide measure of collateral flow (r = -0.44, p < or = 0.0001), as well as an angiographic measure of collateral flow (r = -0.38, p = 0.05). Although ST segment elevation score correlated weakly with the magnitude of myocardium at risk by technetium-99m sestamibi, it was not as strong as infarct location alone in predicting myocardium at risk ([mean +/- SD] anterior 51 +/- 13% left ventricle vs. inferior 17 +/- 10% left ventricle, p < 0.0001). ST segment elevation score was weakly associated with final infarct size (r = 0.34, p = 0.005). A multivariate ECG model was constructed with infarct location as a surrogate for myocardium at risk, ST segment elevation score as a surrogate for estimated collateral flow, and elapsed time to reperfusion from onset of chest pain. All three variables were independently associated with infarct size.

CONCLUSIONS

The initial standard 12-lead ECG can provide insight into myocardium at risk and, to a greater extent, collateral flow and can consequently provide some estimate of subsequent infarct size. However, the confidence limits for such predictors are wide.