Shocking truths about implantable cardioverter defibrillator monitoring zones

An inappropriate shock after reprogramming tachycardia zones

A patient with an implantable cardioverter-defibrillator (ICD) (Abbott®) had episodes of slow monomorphic ventricular tachycardia (VT) and his ICD was programmed with three tachycardia zones. During the follow-up, he received an inappropriate shock. Upon interrogation (of the device), trigeminal pattern binned as ventricular sensing (VS)-VS-ventricular fibrillation (VF) was detected. VF was assumed according to binning system. When VF is present, discrimination algorithms are not available and five consecutive sinus beats are necessary to reset binning system. Catheter ablation was performed to treat VT in order to reprogram tachycardia zones.

Importance of monitoring zones in the detection of arrhythmias in patients with implantable cardioverter-defibrillators under remote monitoring

INTRODUCTION

Implantable cardioverter-defibrillator (ICD) monitoring zones (MZ) provide passive features that do not interfere with the functioning of active treatment zones. However, it is not known for certain whether programming an MZ affects arrhythmia detection by the ICD. The aim of the present study is to assess the clinical relevance of MZ in a population of patients with ICDs.

METHODS

In this retrospective analysis of patients with ICDs, with or without cardiac resynchronization therapy, for primary prevention under remote monitoring, the MZ was analyzed and recorded arrhythmias were assessed in detail.

RESULTS

A total of 221 patients were studied (77% men; age 64±12 years). Mean ejection fraction was 30±12%. The mean follow-up was 63±35 months. One hundred and seventy-four MZ events were documented in 139 patients (62.9%): 74 of non-sustained ventricular tachycardia (NSVT), 42 of supraventricular tachycardia, 44 of atrial fibrillation/atrial flutter, and five cases of noise. Among the 137 patients who presented with arrhythmias in the MZ (excluding two cases with noise detection only), 22 (16.1%) received appropriate shocks and/or antitachycardia pacing (ATP), while of the other 84 patients, 15.5% received appropriate ICD treatment (p=NS). In patients who presented with NSVT in the MZ, 15 (20.5%) received appropriate shocks and/or ATP. In accordance with the MZ findings, physicians decided to change outpatient medication in 41.7% of all patients in whom arrhythmic events were reported.

CONCLUSION

Ventricular and supraventricular arrhythmias are common findings in the MZ of ICD patients. Programming an MZ is valuable in the diagnosis of arrhythmias and may be a useful tool in clinical practice.

A review of the confirmation algorithm and related timing cycles of St. Jude ICDs

The confirmation algorithm of implantable cardioverter-defibrillators (ICDs) functioning in the uncommitted mode verifies the presence of a continuing tachyarrhythmia during or following charging of the capacitor. Confirmation is usually applied in relation to the first shock. The details of the normal reconfirmation process of St. Jude ICDs and its role in delayed shock delivery or other abnormalities have received relatively little attention. This review describes the confirmation process of St. Jude ICDs and provides an illustrative clinical example of delayed shock as a result of a pacing or sensing lead fracture. The fundamental timing cycles of St. Jude ICDs are also reviewed to facilitate understanding of the problems related to the confirmation process.

Prevention of inappropriate ICD shocks in patients with Brugada syndrome

BACKGROUND

In Brugada syndrome implantable cardioverter defibrillator (ICD) therapy is associated with a high rate of inappropriate therapies, mainly due to supraventricular tachyarrhythmias (SVT) (2.7-14.1%/year). Aim of the present study was to evaluate a single ventricular fibrillation (VF) detection zone with a high cut-off rate with respect to prevention of inappropriate ICD shock due to SVT and safety of this programming.

METHODS

Sixty-one consecutive patients (mean age 42.6 +/- 12.9 years; 41 males) diagnosed with Brugada syndrome and implanted with an ICD were included. ICDs were prospectively programmed with a single VF detection zone and a cut-off rate of 222 beats/minute (bpm). A maximum of six shocks with the maximal shock energy were programmed. The minimal follow-up was 1 year.

RESULTS

During a follow-up of 47.6 +/- 23.1 months seven patients (2.91%/year) received appropriate ICD shocks. No patient suffered from syncope or died. Five patients (2.07%/year) received inappropriate ICD shocks: four patients due to T-wave oversensing and only one patient (0.4%/year) due to SVT (atrial fibrillation with a ventricular rate of >222 bpm).

CONCLUSIONS

Programming of a single, high-rate VF zone in patients with Brugada syndrome and an implanted defibrillator is safe. Such programming may be associated with reduced inappropriate defibrillator discharges. A single detection zone with a high VF cut-off rate can be recommended in patients with Brugada syndrome.