Electrocardiographic prediction of the severity of posterior wall perfusion defects on rest 99m Tc-sestamibi myocardial perfusion imaging

Abstract

Background: Myocardial perfusion imaging (MPI) is an excellent non-invasive method for the diagnosis of a posterior wall myocardial infarction (PMI) Using MPI as a surrogate endpoint we sought to identify ECG variables that predict the severity of a PMI. We also investigated the utility of an accepted scoring system (the Selvester QRS score (SQS)) for predicting the severity of PMI. Methods: The study group consisted of 249 patients with posterior wall perfusion defects (PWPD), 143 with only PWPD and 106 with additional defects in other territories. The left ventricle was divided into 9 segments, the uptake in 4 inferior and lateral segments were assessed as PWPD on a 4-point scoring system (0-normal, 3-absent) and stratified as mild, moderate and severe. We used attenuation-correction and gated SPECT to eliminate attenuation artefacts. We explored 58 ECG variables, as criteria for PMI, postero-lateral infarct (PLMI) as well as the SQS. Results: An upright T wave in V1 (67%) was the commonest finding in PWPD group but was not associated with defect severity (p=0.0897). Neither were classic ECG criteria for PMI (21%) and PLMI (19%) (p=0.8901, p= 0.3101). Univariate predictors of severity were SQS (p=0.0001), upright T-wave amplitude in V1>0.2 mV (UTV1) (p=0.0002), T amplitude V2T amplitude V6>0.5 mV (p=0.0022), Q duration in III39 ms (p=0.0042) and R/S ratio V1>1 (p=0.0234). In a multivariate model SQS (p=0.0001) and UTV1 (p=0.0064) were predictive of PWPD severity (c statistics=0.793). Correlation of SQS with PWPD was better in patients with isolated PWPD (R=0.556) than with defects in other territories (R=0.468; p=0.0001). All severe PWPD had SQS≥2. Conclusion: Classic ECG criteria used to diagnose PMI are insensitive and poor predictors of severity as assessed by MPI. An UTV1 will better identify the presence of a previous posterior infarction than other ECG criteria, and is the best predictor of severity. The Selvester QRS score is an effective tool to diagnose both the presence and severity of PMI as defined by MPI. SQS is predictive even in the presence of MPI defects in other territories.