Predictors of an ischemic electrocardiographic response in patients with exercise-induced myocardial ischemia

The determinants of an ischemic electrocardiographic (ECG) response in patients with exercise-induced ischemia on single-photon emission computed tomography (SPECT) remain poorly defined. Specifically, it is unknown whether the occurrence of an ischemic ECG response is related to the extent and/or severity of SPECT ischemia.

Among 3,294 patients who underwent exercise SPECT using a rest thallium-201/exercise Tc-99m sestamibi protocol, 699 (21%) patients had myocardial ischemia defined as summed difference score (SDS) ≥2. The extent of SPECT ischemia was further defined as the total number of segments with difference score ≥1, and severity of ischemia as the largest difference score among all segments. Patients with ischemic ECG changes (n = 315) were significantly older and had a significantly greater prevalence of hyperlipidemia. SDS (7.4 ± 2.2 vs 4.7 ± 1.9, P < .0001), extent (4.2 ± 2.6 vs 2.9 ± 1.7, P < .0001), and severity (2.8 ± 0.9 vs 2.3 ± 0.8, P < .0001) of SPECT ischemia were greater among patients with ischemic ECG changes. In multivariate analysis, age and SDS (which is a composite of the extent and severity of ischemia) were associated with ischemic ECG. When analyzed in a separate model which did not include SDS, both severity of SPECT ischemia (OR 1.42, CI 1.13-1.79) and extent of SPECT ischemia (OR 1.21, CI 1.10-1.33) were independently associated with ischemic ECG.

Among patients with exercise-induced myocardial ischemia by SPECT, age and SDS were associated with ischemic ECG changes. When analyzed separately, the severity and extent of SPECT ischemia were both independent predictors of ischemic ECG changes.