Automatic real-time detection of myocardial ischemia by epicardial accelerometer

Introduction

Epicardial accelerometers have proved to detect myocardial ischemia with high sensitivity [1]. In this combined experimental and clinical study using an epicardial accelerometer, we aimed to test two methods for real-time automated detection of myocardial ischemia.

Methods

One accelerometer (5 × 5 × 2 mm³) was sutured in the perfusion area of the left anterior descending artery (LAD). Epicardial acceleration was simultaneously recorded with ECG, and the ECG QRS complex was automatically detected for timing of systole. From the epicardial acceleration, signal circumferential peak velocity and displacement was automatically calculated within a time interval of 150 ms after peak R on the ECG. Experimental model: in 10 open-chest pigs, regional left ventricular function was reduced by temporary LAD occlusion and global myocardial function changed by esmolol infusion. The myocardial circumferential strain measured by echocardiography was used to confirm ischemia. Clinical model: the accelerometer methods were tested in seven patients, receiving coronary artery bypass grafting. LAD was occluded for 3 minutes before grafting and the accelerometer measurements were compared for hemodynamics, ECG ST-segment analysis and strain by transoesophageal echocardiography.

Results

Accelerometer systolic displacement was superior to systolic velocity to detect ischemia by automated analysis. Accelerometer systolic displacement demonstrated dyskinesia during LAD occlusion in pigs (11.5 ± 2.3 to -1.2 ± 2.8 mm, P < 0.01), while hypokinesia was found in patients (12.8 ± 8.1 to 3.5 ± 4.4 mm, P < 0.01). Ischemia was confirmed by strain echocardiography in both models (P < 0.01). No significant changes in hemodynamics and in the ECG ST segment were seen during LAD occlusion in patients. In the experimental model, esmolol infusion induced fewer changes in the automated accelerometer measurements than LAD occlusion (P < 0.01) and ischemia was detected with a sensitivity of 100% and specificity of 95 to 100%.

Conclusion

Sensitive real-time detection of myocardial ischemia was feasible by the use of automated analysis of continuous epicardial accelerometer signals. This technique may improve real-time detection of ischemia during and after cardiac surgery.