[Evaluation of myocardial viability very early after acute myocardial infarction by ultra-low dose echo-dipyridamole test]

Abstract

Background: After an acute myocardial infarction (AMI), stunned myocardium may cause a reversible left ventricular dysfunction. Dipyridamole echocardiography (0.56 mg*kg-1 over 4' e 0.84 mg*kg-1 over 10') can identify viable myocardium but can also induce ischaemia.

Aim of the study: To evaluate the usefulness of "Infra-low" dose dipyridamole echocardiography for identification of myocardial viability.

Method and results: Of thirty-four consecutive in-hospital patients, thirty (26 males; mean age 59 +/- 11 years) with AMI separately underwent (40 +/- 12 hours from symptoms onset): 1. a baseline resting echo (BASELINE); 2. a low dose dobutamine (DOB) echotest (5-10 mcg*kg-1*m-1 for 5') (DOB5, DOB10); 3. an "infra-low" dose dipyridamole echotest (0.28 mg*kg-1 over 4') (DIP). A pre-discharge resting echo was performed 7 days after admission (follow-up). No patient developed echocardiographic or electrocardiographic signs of ischaemia after DIP, while 4 patients developed ischaemia after DOB. The systolic blood pressure (112 +/- 18 mmHg) did not change after both DOB and DIP. The heart rate was unchanged after DIP (BASELINE = 73 +/- 18 bpm', DIP = 75 +/- 14 bpm'), while it increased after DOB (BASELINE 69 +/- 11 bpm'; DOB5 = 71 +/- 11 bpm', p = 0.02; DOB10 = 74 +/- 12 bpm', p = 0.001). Wall motion score index (WMSI), in a 16-segment model (from 1 = normal to 4 = diskinetic) (BASELINE = 1.64 +/- 0.3), improved after DIP (1.56 +/- 0.36, p < 0.05 vs BASELINE) and after DOB10 (1.50 +/- 0.36, p < 0.05 vs BASELINE) while did not change after DOB5 (1.59 +/- 0.35, p = n.s.). WMSI decreased at follow-up (1.53 +/- 0.31, p < 0.05 vs BASELINE); DIP and DOB10, but not DOB5, correctly predicted the WMSI decrease observed at follow-up. Results of DOB5, DOB10 and DIP were fully concordant in 118 segments (67%) (kappa = 0.54): 13 (7%) with concordant positivity and 105 (60%) with concordant negativity; 58 (33%) segments showed different results. At follow-up 54 (30%) of the 178 segments with baseline dysfunction, observed in 29 survivors, showed an improvement of grade 1 or more (viable). Two patients did not undergo DOB10; therefore, of the 168 segments with baseline dysfunction, in 27 survivors who underwent all tests, 54 (32%) showed an improvement of grade 1 or more (viable) e 114 (68%) showed no improvement (not viable). Of 25 DOB5 "responders" segments, 11 (44%) showed spontaneous recovery at follow-up (true-positive); of 153 "non responders" segments, 110 (72%) showed no spontaneous recovery at follow-up (true-negative). Of 61 DOB10 "responders" segments, 29 (47%) showed spontaneous recovery at follow-up (true positive); of 107 "non responders" segments, 82 (77%) showed no spontaneous recovery at follow-up (true-negative). Of 36 DIP "responders" segments, 19 (53%) showed spontaneous recovery at follow-up (true positive); of 142 "non responders" segments, 107 (75%) showed no spontaneous recovery at follow-up (true-negative). The sensitivity of DOB5, DIP and DOB10 for predicting short-term spontaneous recovery was 20, 35 and 53% (DOB10 vs DOB5: p < 0.001), respectively; specificity was 88, 86 and 71% (DOB5 vs DOB10: p = 0.002; DIP vs DOB10: p = 0.01); the positive value was 44, 52 and 47% (p = n.s.) and the negative predictive value was 72, 75 and 76% (p = n.s.) while the diagnostic accuracy was 67, 70 and 85% (p = n.s.).

Conclusions: "Infra-low" dose dipyridamole echocardiography appears to be a hemodynamically neutral stress which does not modify either heart rate or blood pressure. It allows to explore selectively the viability of stunned myocardium, without eliciting ischaemia; it shows a good overall concordance with low-dose dobutamine and a low sensitivity but an excellent specificity for predicting spontaneous recovery early after AMI.