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

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.

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.

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.

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.

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.