Early detection of acute posterior myocardial infarction using body surface mapping and SPECT scanning.

BACKGROUND: Many patients with non-ST elevation myocardial infarction (NSTEMI) may have posterior STEMI, which should be emergently treated with reperfusion strategies but is difficult to identify by 12-lead ECG.

OBJECTIVES: To compare the initial ECG and body surface map (BSM) for the diagnosis of posterior MI as verified by single-photon emission computed tomography (SPECT) and cTroponin T.

METHODS: Patients with chest pain greater than 20 min at rest with either ST depression of at least 0.1 mV in at least one of leads I, aVL or V1-V6 on ECG or STE at least 0.05 mV in at least one posterior lead on the BSM which underwent early SPECT scan.

RESULTS: Sixty patients (87%, 60 out of 69 with interpretable SPECT) had a posterior wall perfusion defect, all had cTroponinT (>0.09 ng/ml) and thus had posterior MI. Initial ECG showed STE in 24 (40%, 24 out of 60): 36 were non-diagnostic (60%, 36 out of 60). STE on BSM identified inferior MI in seven patients (12%, 7 out of 60), posterior in 32 patients (53%, 32 out of 60), and nine patients had right ventricular (15%, 9 out of 60). Twelve had no STE (20%, 12 out of 60). Of the patients with posterior MI and non-diagnostic ECGs, 53% (19 out of 36) were posterior MI by the BSM and six (17%, 6 out of 36) right ventricular MI only. The BSM correctly identified 53% (32 out of 60) (95% confidence interval 40-66%) of posterior MI. Of the 60 patients with posterior MI, 60% (36) had non-diagnostic ECGs: the BSM identified 42% (25) either as posterior MI or right ventricular MI only.

CONCLUSION: We have shown that the BSM diagnoses significantly more posterior MI than the 12-lead ECG, allowing early identification of these patients so that maximum benefit from early reperfusion strategies can be gained.