Analysis of Troponin I Levels After Spontaneous Implantable Cardioverter Defibrillator Shocks

INTRODUCTION: Serum cardiac troponin I (cTnI) is a sensitive and specific marker for myocardial injury. Myocardial ischemia and/or injury can be a trigger for ventricular arrhythmias. The aim of this study was to assess the frequency and significance of elevated serum cTnI levels after spontaneous implantable cardioverter defibrillator (ICD) shocks. METHODS AND RESULTS: Serial cTnI measurements and ECGs were performed in 35 patients with transvenous ICDs who were admitted after spontaneous ICD shocks. Elevated cTnI levels were found in 18 patients (51%). Acute coronary syndrome was diagnosed in 5 (22%) of 23 patients with known coronary artery disease. After excluding the patients with acute coronary syndrome, elevated cTnI levels were present in 13 (43%) of 30 patients: 18% of patients with < or =3 shocks and 58% of patients with >3 shocks. Patients with elevated cTnI levels received a higher number of shocks (16+/-18 vs 5+/-7; P < 0.05) and had higher total delivered energies (475+/-538 J vs 128+/-184 J; P < 0.05) compared with patients with normal cTnI. Patients with acute coronary syndrome had higher peak cTnI levels (18+/-16 ng/mL) compared with patients with elevated cTnI without acute coronary syndrome (3.8+/-4.3 ng/mL; P < 0.01). CONCLUSION: Serum cTnI rises occur in the majority of patients after multiple (>3) spontaneous ICD discharges but are due to acute coronary syndrome only 14% of the time (22% of the time in patients with known coronary artery disease).