INTRODUCTION: Lead reversal of a dual-chamber (D-C) ICD is a rare but possible event that can occur during device implantation or at the time of generator replacement. The presence of DF-1 connector is a prerequisite for the switch between atrial and pace/sense ventricular lead. The effects may be deleterious for the patient.
CLINICAL CASE: A 86 y-o man was admitted to the hospital for fatigue; ICD malfunction was suspected. Medical history included paroxysmal AF, ICD implantation for ischemic cardiomyopathy, generator replacement one year ago and access to ED for ICD-shock 3 months before: the device check showed an appropriate intervention on VT. Device was programmed in DDD-70 bpm and at the admission the surface ECG showed: a first spike not followed by electrical activity and a subsequent spike after the programmed AV which resulted in atrial depolarization; the latter was followed by spontaneous narrow QRS. Subsequently the ECG showed a paced QRS complex with another spike 80ms later inside the QRS (Fig.1a). The EGMs at device check are represented in Fig.1b. Impedance, threshold and lead sensing parameters were normal except for atrial threshold close to the programmed output. During sensing test the atrial EGM followed the ventricular EGM (Fig.2) and raised the suspicion of 1) atrial undersensing with T-wave oversensing, ruled out by testing different PVARP and atrial sensitivity; 2) Atrial lead dislodgement in the ventricle 3) atrial and ventricular lead connection switch. To better define the problem the threshold test was combined with the surface ECG recording: threshold tests in VVI and AAI showed respectively atrial and ventricular capture on the surface ECG (Fig.3a,3b), which confirmed the inversion of atrial and ventricular pace/sense connections. Subsequent surgical repositioning of the correct lead to the IS1 sensing/pacing RA and RV ports allowed resolution of this problem.
DISCUSSION: Atrial and ventricular lead connection switch is only possible in DF-1 D-C ICD. Diagnosis can easily be missed if the device check is not combined with surface ECG. In this case once the diagnosis was made, it was possible to understand that the ICD-shock occurred 3 months before was inappropriately delivered on a SVT.
CONCLUSION: Atrial and ventricular lead switch diagnosis is complex and often requires additional manoeuvers. The confirmation is crucial to avoid both inappropriate shocks and the failure to treat life-threatening ventricular arrhythmias.
