ELECTROCARDIOGRAPHIC PSEUDO-INFARCT PATTERNS AFTER IMPLANTATION OF CARDIOVERTER-DEFIBRILLATORS

Postoperative electrocardiographic (EGG) changes are frequently presen t after insertion of implantable cardioverter-defibrillators (ICD) and may mimic perioperative myocardial infarction (MI). The purpose of th is study was to assess the incidence and clinical significance of post operative ECG changes in relation to clinical, laboratory, and implant ation data. In 25 (16%) of 156 patients undergoing ICD implantation, s ignificant ECG changes (greater than or equal to 50% reduction in R-wa ve amplitude in greater than or equal to 3 leads or new Q waves in gre ater than or equal to 2 leads) were present 1 to 3 days after the oper ation and persisted at hospital discharge in 12 (8%). Presence of thor acotomy, the total number of induced ventricular fibrillation episodes , and the number of defibrillation shocks required during defibrillati on threshold (DFT) testing correlated with postoperative ECG changes. Other factors associated with a significant R-wave loss in the lateral precordial reads included left-sided pleural effusion, lung infiltrat es or atelectasis, and large defibrillator patch electrodes over the l eft ventricle or the lateral chest wall. Myocardial necrosis documente d by elevated cardiac enzymes occurred in 6 (5%) of 151 patients witho ut significant ECG changes and in 3 (12%) with (p value not significan t). However, postoperative ECG changes associated with elevated enzyme s were indistinguishable from changes unrelated to necrosis. Therefore the sensitivity and specificity of the surface ECG for detection of M I after ICD placement is poor. Multiple factors such as thoracotomy, m yocardial injury from DFT testing, electric insulation, or shielding o f the heart may contribute to the development of electrocardiographic pseudo-infarct patterns.