Distal Right Ventricular Coil Position Reduces Defibrillation Thresholds

Patients with a high defibrillation threshold: Approaches to management

Implantable cardioverter-defibrillators (ICDs) have revolutionized the prognosis for patients at elevated risk of ventricular tachyarrhythmias. For safety, defibrillation should be effective with a minimum of 10 J below the device's maximum energy. While modern ICDs rarely deliver ineffective shocks in primary prevention, the surge in managing severe heart failure patients has led to an increased number of patients with high defibrillation thresholds (DFTs). This article elucidates the potential causes of high DFT, including clinical factors, lead and device placement, the presence of a Left Ventricular Assist Device (LVAD), prolonged ventricular arrhythmias, shock vectors, waveform tilt, medications, and manufacturer-specific options. We also detail management strategies, highlighting alternative shock coil placements, practical recommendations, and case studies from our institution. Our management algorithm suggests addressing preventable causes, re-evaluating coil positions, considering non-invasive system modifications, upgrading to a higher-capacity device, and adding extra coil(s).

Significance of intraoperative testing in right-sided implantable cardioverter-defibrillators

Background

Implantation of implantable cardioverter-defibrillators (ICD) from the left pectoral region is the standard therapeutical method. Increasing numbers of system revisions due to lead dysfunction and infections will consecutively increase the numbers of right-sided implantations. The reliability of devices implanted on the right pectoral side remains controversially discussed, and the question of testing these devices remains unanswered.

Methods

In a prospectively designed study all 870 patients (60.0±14 years, 689 male) who were treated with a first ICD from July 2005 until May 2012 and tested intraoperatively according to the testing protocol were analyzed. The indication for implantation was primary prophylactic in 71.5%. Underlying diseases included ischemic cardiomyopathy (50%), dilative cardiomyopathy (37%), and others (13%). Mean ejection faction was 27±12%. Implantation site was right in 4.5% and left in 95.5%.

Results

Five patients supplied with right-sided ICD (13%, p = 0.02 as compared to left-sided) failed initial intraoperative testing with 21 J. 3 patients were male. The age of the patients failing intraoperative testing with right-sided devices appeared higher than of patients with left-sided devices (p = 0.07). The ejection fraction was 28±8%. All patients reached a sufficient DFT ≤ 21 J after corrective procedures.

Conclusion

Implantation of ICDs on the right side results in significantly higher failure rate of successful termination of intraoperatively induced ventricular fibrillation. The data of our study suggest the necessity of intraoperative ICD testing in right-sided implanted ICDs.

Covering sleeves can shield the high-voltage coils from lead chatter in an integrated bipolar ICD lead

AIMS

Integrated bipolar implantable cardioverter-defibrillator (ICD) leads use the distal high-voltage coil as both the ventricular sensing anode and the distal shocking electrode. Mechanical interactions between the distal ICD coil and other intracardiac leads have been reported to result in electrical oversensing and inappropriate ICD therapies. We sought to determine whether covering sleeves over the high-voltage coils of an integrated bipolar ICD lead could prevent sensed artefact from mechanical lead interactions.

METHODS AND RESULTS

Endotak Reliance 0157 and Endotak Reliance-G 0185 leads, the latter with expanded polytetrafluoroethylene (ePTFE) sleeves covering the high-voltage coils, were connected to ICD generators and the leads were submerged in saline. Device programmers were used to communicate with the ICD generators, providing real-time electrogram recording throughout testing. A series of mechanical interactions were performed with the ICD leads, including sliding and striking each distal coil against metal and non-metal components of other ICD and pacemaker leads. All direct metal-metal interactions resulted in sensed electrical artefact, including interactions between the bare ICD coil and another bare ICD coil or metal pacemaker ring. Identical mechanical interactions where metal-metal contact was prevented due to an interposed ePTFE covering sleeve were electrically silent with no sensed artefact.

CONCLUSIONS

A covering sleeve over the distal high-voltage coil of an integrated bipolar ICD lead can mechanically shield the lead from metal-metal interactions, which might otherwise result in sensed artefact and inappropriate ICD therapies or withholding of pacing output. This finding has implications for lead selection when a new ICD lead is to be implanted adjacent to abandoned intracardiac leads or lead fragments.

A Biventricular ICD System with Biventricular Defibrillation

We describe the case of a 59-year-old gentleman with severe dilated cardiomyopathy requiring implantation of a dual-chamber biventricular implantable cardioverter-defibrillator (ICD). High defibrillation thresholds (DFT) were encountered at implant with an inadequate defibrillation safety margin. Testing of all possible shock vectors/polarities with and without the SVC coil and optimization of the distal RV coil position all proved inadequate. A satisfactory defibrillation safety margin was achieved following placement of a second lead in the coronary sinus to enable biventricular defibrillation. This case highlights an additional strategy for combating high DFTs and is an option even in dual-chamber biventricular ICD systems.