Comparison of Hyperemic Impedance Echocardiography with Dobutamine Stress Echocardiography to Detect Inducible Myocardial Ischemia: A Pilot Study

Abstract

Background: Stress echocardiography using exercise or pharmacological stressors is either contraindicated or associated with significant side effects in some patients. This pilot study was designed to evaluate a new technique, hyperemic impedance echocardiography (HIE). It is based on reactive coronary hyperemia when transient limb ischemia is induced by tourniquet inflation. We hypothesized that this physiologic coronary hyperemia can identify inducible myocardial ischemia by assessment of regional wall motion abnormalities on echocardiography when compared with dobutamine stress echocardiography (DSE).

Methods: Twenty consecutive outpatients with suspected stable coronary artery disease (CAD) who underwent clinically indicated DSE were recruited for performance of HIE after informed consent was obtained. Standard graded dobutamine infusion protocol from 5 to 40 μg/kg per min was used for DSE. HIE was performed by inflating tourniquets at a pressure of 10 mmHg below the systolic blood pressure for 1 minute in three of four extremities at a time for total of four cycles. Echocardiography was performed immediately after the last rotating tourniquet deflation. DSE and HIE were classified as abnormal for development of new or worsening wall motion abnormality in at least one myocardial segment. Test characteristics were also determined for a subset of these patients (n = 12) who underwent clinically indicated coronary angiography.

Results: Hyperemic impedance echocardiography showed 86% sensitivity, 67% specificity, 86% positive predictive value, and 67% negative predictive value with a test accuracy of 80% to detect inducible myocardial wall motion abnormalities when compared with DSE. HIE also showed 83% sensitivity, 75% negative predictive value with a test accuracy of 66.7% for detection of significant (≥50% diameter stenosis) CAD on coronary angiography.

Conclusion: In this pilot study, HIE was a feasible, safe, and promising method for detection of inducible myocardial ischemia by assessment of regional wall motion abnormalities when compared to DSE and coronary angiography. Larger studies are needed to confirm these findings.

Keywords: dobutamine stress echocardiography; hyperemic impedance echocardiography; rotating tourniquet.