Incidence of very high defibrillation thresholds (DFT) and efficacy of subcutaneous (SQ) array insertion during implantable cardioverter defibrillator (ICD) implantation

Azygous Vein Coil Implantation in Left Ventricular Assist Device Patients: A Hands-on Approach

Recently, there have been reports of left ventricular assist device (LVAD) patients presenting with multiple ineffective implantable cardioverter-defibrillator (ICD) shocks. In such patients, the placement of an azygous vein coil by providing an alternative anteroposterior trajectory of the electrical shock vector can enable successful defibrillation. This review discusses a hands-on approach to azygous vein coil implantation. Additionally, we compare our tools and technique to those that have been previously described by other operators. From 2018 to 2021, eight patients were identified who underwent azygous vein coil implantation at MedStar Washington Hospital Center using a specific technique and tools. Demographic and procedural data were obtained by a retrospective review of patient charts, procedure logs, fluoroscopy, and venography performed during coil implantation. The indication for azygous vein coil implantation was ineffective ICD shocks in seven patients. The presenting rhythm was ventricular fibrillation in six (75%) cases and sustained ventricular tachycardia in two (25%) cases. Using the approach described, we were able to successfully implant an azygous vein coil in all eight (100%) patients. There were no procedure-related complications. Postimplantation, defibrillation threshold (DFT) testing was successfully performed in six of eight (75%) patients. One patient failed DFT testing despite placement of an azygous vein coil. In another patient, DFT testing was not performed because the patient was in atrial fibrillation and was not systemically anticoagulated. In conclusion, the placement of an azygous vein coil in LVAD patients with failed ICD shocks using the tools and technique described in this report is safe and highly efficacious (successful in 100% of cases).

Pre- and post-treatment with amiodarone for elective electrical cardioversion of atrial fibrillation: a systematic review and meta-analysis

AIMS

Clinicians frequently pre-treat patients with amiodarone to increase the efficacy of electrical cardioversion for atrial fibrillation (AF). Our objective was to determine the precise effects of amiodarone pre- and post-treatment on conversion efficacy and sinus rhythm maintenance.

METHODS AND RESULTS

We conducted a systematic review and meta-analysis of trials comparing pre- and post-treatment for electrical cardioversion with amiodarone vs. no therapy on (i) acute restoration and (ii) maintenance of sinus rhythm after 1 year. We searched MEDLINE and EMBASE from inception to July 2018 for randomized controlled trials. We evaluated the risk of bias for individual studies with the Cochrane tool and overall quality of evidence with the GRADE framework. We identified eight eligible studies (n = 1012). Five studies were deemed to have unclear or high risk of selection bias. We found the evidence to be of high quality based on GRADE. Treatment with amiodarone (200-800 mg daily for 1-6 weeks pre-cardioversion; 0-200 mg daily post-cardioversion) was associated with higher rates of acute restoration [relative risk (RR) 1.22, 95% confidence interval (CI) 1.07-1.39, P = 0.004, n = 1012, I2 = 65%] and maintenance of sinus rhythm over 13 months (RR 4.39, 95% CI 2.99-6.45, P < 0.001, n = 695, I2 = 0%). The effects of amiodarone for acute restoration were maintained when considering only studies at low risk of bias (RR 1.22, 95% CI 1.10-1.36, P < 0.001, n = 572, I2 = 0%). Adverse effects were typically non-serious, occurring in 3.4% (6/174) of subjects receiving amiodarone.

CONCLUSION

High-quality evidence demonstrated that treatment with amiodarone improved the restoration and maintenance of sinus rhythm after electrical cardioversion of AF. Short-term amiodarone was well-tolerated.

Risk Factors for Inadequate Defibrillation Safety Margins Vary With the Underlying Cardiac Disease: Implications for Selective Testing Strategies

INTRODUCTION

In view of the shift from routine toward no or selective defibrillation testing, optimization of the current risk stratification for inadequate defibrillation safety margins (DSMs) could improve individualized testing decisions. Given the pathophysiological differences in myocardial substrate between ischemic and nonischemic heart disease (IHD/non-IHD) and the accompanying differences in clinical characteristics, we studied inadequate DSMs and their predictors in relation to the underlying etiology.

METHODS AND RESULTS

Cohort of routine defibrillation tests (n = 785) after first implantable cardioverter defibrillator (ICD)-implantations at the Radboud UMC (2005-2014). A defibrillation threshold >25 J was regarded as an inadequate DSM. In total, 4.3% of patients had an inadequate DSM; in IHD 2.5% versus 7.3% in non-IHD (P = 0.002). We identified a group of non-IHD patients at high risk (13-42% inadequate DSM); the remainder of the cohort (>70%) had a risk of only 2% (C-statistic entire cohort 0.74; C-statistic non-IHD 0.82). This was based upon two identified interaction terms: (1) non-IHD and age (aOR 0.94 [95% CI 0.91-0.97]); (2) non-IHD and the indexed left ventricular (LV) internal diastolic diameter (aOR 3.50 [95% CI 2.10-5.82]).

CONCLUSION

The present study on risk stratification for an inadequate DSM not only confirms the importance of making a distinction between IHD and non-IHD, but also shows that risk factors in an entire cohort (LV dilatation, age) may only apply to a subgroup (non-IHD). Appreciation of this concept could favorably affect current risk stratification. If confirmed, our approach may be used to optimize individualized testing decisions in an upcoming era of non-routine testing.

Frequency characteristics and associations with the defibrillation threshold of ventricular fibrillation in patients with implantable cardioverter defibrillators

OBJECTIVE

The dominant frequency (DF) in frequency analyses is considered to represent the objective cycle length and complexity of activation under conditions of ventricular fibrillation (VF). However, knowledge regarding the mechanisms determining the DF in human VF is limited. We studied the characteristics of the DF of human VF and relationship between DF and the defibrillation threshold.

METHODS

Seventy-two implantable cardioverter-defibrillator patients and 211 VF were studied. Using defibrillation tests, we performed a frequency analysis with fast Fourier transformation. The correlations between DF and clinical characteristics, including the defibrillation threshold, were assessed.

RESULTS

The mean DF of all induced VFs was 5.2±0.8 Hz. The patients were divided into two groups according to DF: the low-DF (DF <5.2 Hz, n=32) and high-DF (DF ≥5.2 Hz, n=40) groups. The frequency of structural heart disease was significantly higher in the low-DF group. In addition, the QRS duration, QT interval and effective refractory period of the right ventricle (RV-ERP) were significantly longer in the low-DF group. A multivariate analysis showed RV-ERP to be the only independent predictor of DF. Excluding patients receiving group III anti-arrhythmic drugs, which are known to have potent defibrillation threshold effects, the defibrillation threshold was significantly lower in the low-DF group (p=0.026).

CONCLUSION

We found that the DF of human VF is associated with underlying heart disease, the cardiac function, cardiac conduction, ventricular refractoriness and defibrillation threshold. Our findings may be useful for identifying and managing patients with a high defibrillation threshold.

A Novel Solution for the High Defibrillation Threshold in Patients with a DF-4 Lead: Adding a High Voltage Adaptor/Splitter

A high defibrillation threshold occurs in approximately 6% of implants. The defibrillation threshold can be improved by addition of a defibrillation lead. However, the DF-4 high energy ICD header precludes the addition of a defibrillation lead. Here we report on use of a new high voltage adaptor/splitter that enables the addition of an extra defibrillation lead.

Implantation of additional subcutaneous array electrode reduces defibrillation threshold in ICD patients - preliminary results

INTRODUCTION

Among the recipients of implantable cardioverter-defibrillators (ICDs), there is a group of patients in whom the defibrillation threshold (DFT) is too high to enable a sufficient safety margin between the DFT and the maximal available output of the device. The aim of the study was to investigate the ability of an additionally implanted single-coil subcutaneous array electrode to reduce the DFT in such patients.

MATERIAL AND METHODS

Medtronic 6996SQ electrode was implanted in 15 patients selected from our follow-up group of 741 ICD patients: 10 of them had insufficient post-implant DFT safety margin, and 5 had ineffective first maximal energy shock as recorded by the device. In 6 cases the patients had CRT-D devices, in 5 cases - dual-chamber ICDs, and in 4 cases - single-chamber ICDs. In all patients but one the defibrillating electrode was single-coil. In one patient it was dual-coil. The underlying disease was coronary artery disease in 10 patients, dilated cardiomyopathy in 4 patients and hypertrophic cardiomyopathy in 1 patient.

RESULTS

The subcutaneous electrode was successfully implanted in all the patients qualified for the procedure. No technical issues or perioperative complications were observed. Mean DFT was reduced from 33.3 ±4.1 J before the procedure to 25.3 ±4.4 J after the implantation procedure (p < 0.01).

CONCLUSIONS

Our results show that the use of a single-coil subcutaneous electrode to reduce the DFT is a safe and effective procedure. Further studies are necessary to confirm these results.