Predictors of high defibrillation threshold in the modern era

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).

Non-traditional implantable cardioverter-defibrillator configurations and insertion techniques: a review of contemporary options

Implantable cardioverter-defibrillators (ICDs) have revolutionized the treatment of acquired or inherited cardiac diseases associated with a high risk of sudden cardiac death due to ventricular tachyarrhythmias. Contemporary ICD devices offer reliable arrhythmia detection and discrimination algorithms and deliver highly efficient tachytherapies. Percutaneously inserted transvenous defibrillator coils with pectoral generator placement are the first-line approach in the majority of adults due to their extensively documented clinical benefit and efficiency with comparably low periprocedural implantation risks as well as the option of providing pain-free tachycardia treatment via anti-tachycardia pacing (ATP), concomitant bradycardiaprotection, and incorporation in a cardiac resynchronization therapy if indicated. Yet, expanding ICD indications particularly among younger and more complex patient groups as well as the increasingly evident long-term consequences and complications associated with intravascular lead placements promoted the development of alternative ICD configurations. Most established in daily clinical practice is the subcutaneous ICD but other innovative extravascular approaches like epicardial, pericardial, extra-pleural, and most recently substernal defibrillator coil placements have been introduced as well to overcome shortcomings associated with traditional devices and allow for individualized treatment strategies tailored to the patients characteristics and needs. The review aims to provide practical solutions for common complications encountered with transvenous ICD systems including restricted venous access, high defibrillation/fibrillation thresholds (DFTs), and recurrent device infections. We summarize the contemporary options for non-traditional extravascular ICD configurations outlining indications, advantages, and disadvantages.

Defibrillation threshold testing during implantable cardioverter defibrillator implantation: 5-year follow-up

PURPOSE

Defibrillation threshold (DFT) testing is a routine practice in some Asian countries for patients receiving an implantable cardioverter defibrillator (ICD). However, there are few long-term data about the necessity of intraoperative DFT testing in an Asian population. We investigated the safety of DFT testing and the long-term clinical outcomes in Asian patients undergoing ICD implantation.

METHODS

All patients undergoing de novo transvenous ICD implantation were randomized to undergo periprocedural DFT testing. The study included 67 patients (50 males; 51.5 ± 16.9 years) who underwent ICD implantation with (n = 33) or without (n = 34) intraoperative DFT testing between March 2012 and February 2014. We compared first-shock success, composite safety end points (the sum of complications recorded at 30 days), arrhythmic death, and all-cause mortality.

RESULTS

The baseline clinical characteristics and the procedural-related adverse event rate (3.0% with DFT vs. 0% with non-DFT, p = 0.214) did not differ between groups. The programmed output of the first shock was lower in the DFT testing group (22.9 ± 4.4 J vs. 25.3 ± 5.4 J, p = 0.007). However, there were no significant differences between groups for all-cause mortality (12.1% vs. 17.6%, p = 0.526) or first-shock success rate for ventricular arrhythmia (100% vs. 88.2%, p = 0.471).

CONCLUSIONS

There were no between-group differences in periprocedural safety, complications, and long-term clinical outcomes. Our results suggest that DFT testing in Asian patients allows reduction of the programmed output of the first shock, but does not affect long-term clinical outcomes.

Coronary vein defibrillator coil placement in patients with high defibrillation thresholds

BACKGROUND

Elevated defibrillation threshold (DFT) occurs in 2%-6% of patients undergoing implantable cardioverter defibrillator (ICD) implantation. Adding a defibrillation coil in the coronary sinus (CS) or its branches can result in substantial reductions in the mean DFT. However, data regarding acute success and long-term stability remain lacking. We report our experience with this bailout strategy.

METHODS

Patients with elevated DFT at implantation (safety margin at implantation <10 J) and those with failed ICD shocks for ventricular arrhythmias (VA) referred for high DFT underwent placement of an additional defibrillation coil in the CS. DFT testing was performed at the completion of the implantation procedure. External potentially reversible factors were excluded. High-output devices were systematically used.

RESULTS

Four patients with high DFT at implantation and two with several failed shock attempts underwent placement of a defibrillation coil in the CS. Mean age was 41.8 (23-78). They presented a mean LVEF of 21% (15-30), QRS-complex duration of 109.8 milliseconds (87-168), body surface area of 1.96 m2 (1.45-2.58), and a mean R wave of 16.3 mV (8-27). Defibrillation coil implantation in the CS (final shocking configuration of right ventricle as anode and left ventricle (LV) plus can as cathode) was associated with successful DFT testing in all. Three patients had a concomitant LV lead for biventricular pacing. During a mean follow-up of 54.67 months (10-118), two patients experienced successful ICD shocks for VA (one of them also presented inappropriate shocks because of the fast conducting atrial fibrillation).

CONCLUSIONS

Positioning of a defibrillation coil in the CS can result in a substantial reduction in mean DFT and associates with optimal long-term stability.

Defibrillation Threshold Testing: Current Status

When the transvenous ICD initially came into use for primary and secondary prevention of sudden cardiac death, defibrillation threshold (DFT) testing was universally performed. However, DFT testing is no longer routinely recommended for transvenous ICD implantation except in certain situations. Risk scores can help guide the decision to perform DFT testing. The subcutaneous ICD represents an area of uncertainty, with limited data available regarding the role of DFT testing in these devices. Current guidelines give a class I recommendation for performing DFT testing at the time of implant. Further studies are needed before this recommendation can be safely dismissed.

Thoracoscopic Implantation of An Array Electrode in the Pericardium Transverse Sinus to Reduce Defibrillation Threshold

Among the implantable cardioverter defibrillator recipients, there is still a subgroup of patients in whom the defibrillation threshold is too high and the maximal shock output of the implantable cardioverter defibrillator can fail to terminate a ventricular arrhythmia. We report a new thoracoscopic minimally invasive approach to place a standard array electrode in the transverse pericardial sinus of a patient implanted with a cardiac resynchronization and defibrillation therapy device with persistent high defibrillation threshold. This approach was developed to achieve very low shock impedance with a consequent increase in the current flow and reduction of defibrillation threshold.

The association between defibrillation shock energy and acute cardiac damage in patients with implantable cardioverter defibrillators

BACKGROUND

The aim of this study was to establish a minimally invasive defibrillation testing (DT) protocol for patients with implantable cardioverter defibrillators (ICDs).

METHODS

Two different energy DTs were performed, immediately after (15 J-DT) and 7 days after (≤10 J-DT) device implantation, in 20 consecutive ICD implantation patients. Cardiac-troponin T (c-TNT) and heart-type fatty acid binding protein (H-FABP) levels were measured before implantation, 2 h after implantation, and 1 day after each DT. For an additional 122 patients with ICD, we retrospectively analyzed 203 DTs immediately and 7 days after device implantation.

RESULTS

Serum c-TNT levels were significantly elevated 2 h after 15 J-DT [0.008 (0.004-0.019) vs. 0.053 (0.037-0.068) ng/mL, p<0.001], but not ≤10 J-DT [0.007 (0.004-0.018) ng/mL]. Similarly, serum H-FABP levels were significantly elevated 2 h after 15 J-DT (2.9±1.5 vs. 6.4±3.4 ng/mL, p<0.001), but not ≤10 J-DT (2.7±1.5 ng/mL). The changes in c-TNT and H-FABP levels between baseline and 2 h after DT were significantly greater for 15 J-DT compared with ≤10 J-DT [c-TnT: 0.039 (0.029-0.060) vs. 0 (0-0.003) ng/mL, p<0.001; H-FABP: 3.6±2.8 vs. -0.16±1.1 ng/mL, p<0.001]. The success rates of the initial shocks delivered for ventricular fibrillation were no different between ≤10 J-DT (85% [78/92]) and ≥15 J-DT (92% [103/111]).

CONCLUSIONS

Elevated levels of myocardial damage markers such as c-TNT and H-FABP were not found after ≤10 J-DT. In addition, an acceptable success rate was confirmed in ≤10 J-DT.

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.

The Effect of Direct Current Stimulation versus T-Wave Shock on Defibrillation Threshold Testing

INTRODUCTION

There are several methods to induce ventricular fibrillation (VF) during defibrillation threshold (DFT) testing. Delivering a shock at a critical time during the T wave (T-shock) is the conventional approach, while delivering a constant direct current voltage (DC stim) from the implantable cardioverter defibrillator is an alternative method. Only a few reports compare VF induction methods. The purpose of this study was to evaluate the effects and safety of DC stim versus T-shock.

METHODS

We retrospectively investigated 414 consecutive patients undergoing DFT testing. We compared the two groups (DC stim and T-shock) with respect to clinical characteristics, electrocardiogram (ECG) changes, and complications.

RESULTS

Ventricular arrhythmia, including ventricular tachycardia (VT) and VF, was induced by DC stim in 93 patients or T-shock in 321 patients. No more than three attempts were performed during one procedure. There was no significant difference in the baseline ECG, induced tachycardia cycle length (TCL), or complications between the two groups. However, the induced TCL was significantly shorter than the clinical TCL regardless of induction method (P = 0.001). Five patients suffered major complications (i.e., electromechanical dissociation or incessant VT). A history of atrial fibrillation was significantly greater in patients with major complications than the others (80% vs 24%, P = 0.004), and was an independent predictor on multivariate analysis.

CONCLUSIONS

There is no significant difference in induced TCL or complications between the DC stim and T-shock. The induced TCL is significantly shorter than clinical TCL regardless of induction method.

Intra-operative defibrillation testing and clinical shock efficacy in patients with implantable cardioverter-defibrillators: the NORDIC ICD randomized clinical trial

AIMS

This trial was designed to test the hypothesis that shock efficacy during follow-up is not impaired in patients implanted without defibrillation (DF) testing during first implantable cardioverter-defibrillator (ICD) implantation.

METHODS AND RESULTS

Between February 2011 and July 2013, 1077 patients were randomly assigned (1 : 1) to first time ICD implantation with (n = 540) or without (n = 537) DF testing. The intra-operative DF testing was standardized across all participating centres, and all ICD shocks were programmed to 40 J irrespective of DF test results. The primary end point was the average first shock efficacy (FSE) for all true ventricular tachycardia and fibrillation (VT/VF) episodes during follow-up. The secondary end points included procedural data, serious adverse events, and mortality. During a median follow-up of 22.8 months, the model-based FSE was found to be non-inferior in patients with an ICD implanted without a DF test, with a difference in FSE of 3.0% in favour of the no DF test [confidence interval (CI) -3.0 to 9.0%, Pnon-inferiority <0.001 for the pre-defined non-inferiority margin of -10%). A total of 112 procedure-related serious adverse events occurred within 30 days in 94 patients (17.6%) tested compared with 89 events in 74 patients (13.9%) not tested (P = 0.095).

CONCLUSION

Defibrillation efficacy during follow-up is not inferior in patients with a 40 J ICD implanted without DF testing. Defibrillation testing during first time ICD implantation should no longer be recommended for routine left-sided ICD implantation.

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.

Predictors of high defibrillation threshold in patients with implantable cardioverter-defibillator using a transvenous dual-coil lead

BACKGROUND

Defibrillation testing (DT) is considered a standard procedure during implantable cardioverter-defibrillator (ICD) implantation. However, little is known about the factors that are significantly related to patients with high defibrillation threshold (DFT) using the present triad system.

METHODS AND RESULTS

We examined 286 consecutive patients who underwent ICD implantation with a transvenous dual-coil lead and DT from December 2000 to December 2011. We defined patients who required 25 J or more by the implanted device as the high DFT group, and those who required less than 25 J as the normal DFT group. For each patient, assessment parameters included underlying disease, comorbidities, NYHA functional class, drugs, and echocardiographic measures. The high DFT group consisted of 12 patients (4.2%). Multivariate analysis identified 3 independent predictors for high DFT: atrial fibrillation (odds ratio (OR) 4.85, 95% confidence interval (CI) 1.24-22.33, P=0.023), hypertension (OR 4.01, 95% CI 1.08-15.96, P=0.039), thickness of interventricular septum (IVS) >12 mm (OR 4.82, 95% CI 1.17-20.31, P=0.030).

CONCLUSIONS

Atrial fibrillation, hypertension and IVS hypertrophy were significantly associated with high DFT. Identification of such patients could help to lower the risk of complications with DT.