Defibillator Electrogram T Wave Alternans as a Predictor of Spontaneous Ventricular Tachyarrhythmias in Defibrillator Recipients

Background Although T wave alternans (TWA) and the T wave peak-to-end (Tpte) interval are associated with vulnerability to ventricular tachyarrhythmia (VT), no previous reports have demonstrated that TWA immediately precedes spontaneous VT in the human ambulatory setting. Methods and Results Stored electrograms from the implantable cardioverter defibrillators (ICD) of 74 patients (59 males, 55.3 +/- 12.2 years) were analyzed. TWA (Delta T amplitude), Tpte interval, QT interval, and RR intervals were measured from magnified digital images immediately before spontaneous VT (VTClinical; n=73), or immediately after ICD shocks during artificially-induced VT (VTInduced; n=74) or inappropriate shocks (Shock(Inapp); 11=6). (1) TWA was significantly greater in VTClinical than VTInduced (P<0.01) or Shock(Inapp) (P<0.001), but Tpte was not (P=NS). (2) In the VTClinical group, TWA was significantly greater in patients with ischemic VT than in those with non-ischemic cardiomyopathy or idiopathic VF (P<0.05). (3) In the same patient, the TWA for VTClinical was significantly greater than that for VTInduced (P<0.01). Conclusion T A measured from ICD electrograms is significantly greater immediately before spontaneous VT than immediately after inappropriate shocks or shocks during induced VT. These findings indicate that repolarization alternans plays an important role in the induction of VT in humans.