Electrocardiographic changes after dipyridamole infusion in patients undergoing myocardial perfusion imaging

Although the diagnostic and prognostic importance of perfusion defects has been clearly established, the meaning of the development and characteristics of electrocardiographic (ECG) changes during dipyridamole infusion is less well defined. This study tries to evaluate the prevalence and significance of ECG changes after dipyridamole infusion and their relation to ischemia in myocardial perfusion single-photon emission computed tomography (SPECT).

Two hundred patients underwent 2-day dipyridamole stress/rest Tc-99m-sestamibi myocardial perfusion SPECT. Basal and post dipyridamole ECGs were analyzed. Myocardial perfusion images were interpreted visually and semiquantitatively.

New ECG changes were noted in 20.2% of cases and consisted of 1.1% T-wave flattening, 1.1% T-wave inversion and 14.8% ST depression and 4.2% psuedonormalization. Abnormal ECG changes were noted after dipyridamole infusion in approximately 27.7% of patients with and 14.3% of patients without reversible defect in myocardial perfusion SPECT. A new ST depression was noted in lateral leads in 72.2% of new ST changes. The mean post-dipyridamole heart rate increment in patients with reversible or partially reversible defects was significantly lesser than in patients with normal myocardial perfusion SPECT. In addition, the corrected QT interval (QTc) increment in patients with reversible defects was significantly more than in patients with fixed defects; however, there was no difference when compared with patients with no defects. Using linear regression model, the severity of ST depression and QTc increment were significant predictors of summed difference score. Sensitivity, specificity, and negative and positive predictive values of ST-segment depression for the diagnosis of ischemia were 20.2, 89.5, 60.7, and 58.4%, respectively.

The most common ECG change seen after dipyridamole infusion is ST-segment depression. The new ST-segment depression after dipyridamole infusion is highly specific for ischemia. Reversible defects are associated with a lesser increment in heart rate, whereas QTc increment and severity of ST segment depression were significant predictors of summed difference score.