[The echo-nitrate test for the detection of viable myocardium after a myocardial infarct: a comparison with delayed-acquisition thallium scintigraphy].

BACKGROUND

The aim of this study was to evaluate the ability of echocardiography, associated with nitroglycerin infusion, in the detection of myocardial viability in patients with recent infarction.

METHODS

Fourteen patients (11 male, 3 female, mean age 59 +/- 8 years) with first acute myocardial infarction (12 Q wave, 2 non-Q wave) underwent predischarge (18 +/- 3 days) nitrate echocardiography. All patients underwent delayed planar thallium scintigraphy within four weeks from AMI. Nitrate echocardiography was performed with a nitroglycerin infusion starting from 0.4 mcg/Kg/min every 5 minutes up to 2.0 mcg/Kg/min; the test was terminated with an improvement of wall motion abnormalities or with a drop of systolic blood pressure > or = 20%. Wall motion abnormalities were evaluated with a 16-segment wall motion score index (WMSI). Thallium was performed after a symptom-limited exercise test, after 3 and 24 hours. The left ventricle was divided in 15 regions. Thallium was considered the gold standard for myocardial viability.

RESULTS

Basal echo identified 59 dyssynergic segments: of these, 12 (20%-6 patients) showed improvement in contractility during nitrate echocardiography at a mean dose of 0.9 +/- 0.3 mcg/Kg/min. WMSI decreased from 1.42 +/- 0.22 to 1.27 +/- 0.13 (p = 0.022), with no significant change of haemodynamic data (mean systolic blood pressure from 125 to 112 mmHg; mean heart rate from 66 to 76 beats/min; mean rate/pressure product from 8415 to 8848; all p = ns). Thallium scintigraphy showed 40 fixed defects (19%-7 patients) and 10 (4.7%-7 patients) late reversible defects. 20% of the 3-hour fixed defects improved at 24-hour imaging. 5/7 patients with echo improvement had 24-hour reversible defects, while 6/7 with no WMSI improvement had 24-hour fixed defects. Therefore, nitrate echocardiography demonstrated 71% sensitivity, 86% specificity, 83% positive predictive value, 75% negative predictive value and 78% accuracy.

CONCLUSIONS

Nitrate echocardiography may be a feasible and low cost method in the detection of myocardial viability after myocardial infarction, but awaits further validation.