Comparison of electrocardiogram and intrathoracic electrogram signals for detection of ischemic ST segment changes during normal sinus and ventricular paced rhythms

Introduction: The aim of this study was to compare surface ECGs with electrograms (EGM) that are available from implanted devices for the ability to detect ischemic ST segment changes during normal sinus (NS) and ventricular paced (VP) rhythms. Methods and Results: ECG leads I, II, and V-2, right atrial ring to left pectoral patch (representing the can of the device), right ventricular ring to left pectoral patch, and right atrial ring to right ventricular ring EGM were recorded continuously during percutaneous transluminal coronary angioplasty. One balloon inflation (greater than or equal to60 sec) was analyzed from each of 22 NS and 22 VP subjects. The parameter DeltaST was defined as the maximum absolute ST segment deviation (from isoelectric) during the first 60 seconds of inflation, measured relative to the baseline (preinflation) ST segment deviation. For EGM, a normalized DeltaST was defined as the DeltaST divided by the ratio of QRS amplitudes of EGM to ECG. During NS, the DeltaST for EGM (0.43 mV) was significantly larger than that of ECG (0.09 mV, P = 0.0001) but the normalized DeltaST for EGM (0.11 mV) was comparable to that of ECG (0.09 mV, P = 0.45). During VP, the AST for EGM (1.08 mV) was significantly larger than that of ECG (0.17 mV, P = 0.0001), but the normalized AST for EGM (0.11 mV) was significantly smaller than that of ECG (0.17 mV, P = 0.02). Conclusion: During both NS and VP, ischemic ST segment changes were significantly larger in EGM than in ECG. Much of this difference appears to be related to larger amplitudes of EGM signals.