An intuitive method to reduce the defibrillation threshold: a case report

Background

Defibrillation threshold (DFT) testing is done to assess whether proper sensing of ventricular fibrillation and adequate safety margin for defibrillation are present in an implantable cardioverter defibrillator (ICD). This case report presents an intuitive method for lowering the DFT. It may be used on a larger scale in other patients with high DFTs when other methods for lowering the DFT (changing medications, adjusting the device, and adding coils) are not feasible or preferable to use.

Case summary

A 64-year-old male presented to the emergency room with failed appropriate shocks from his ICD. Device interrogation revealed that he failed his first maximum output shock before subsequent shock at the same polarity and output succeeded, suggesting a high DFT. Therefore, the DFT needs to be lowered in our patient. After considering the potential efficacy and risk of a number of traditional options, we used an intuitive method whereby the right ventricular (RV) coils of two separate leads were combined via a y-adapter. This method successfully lowered the patient's DFT, and he received successful shocks from his ICD over the next 9 months before reaching end-stage heart failure. He received a transplant, and the device and transvenous leads, except for the superior vena cava coil, were successfully removed.

Discussion

Combining two RV coils from different locations may lower the DFT. This method may be considered in the larger population in cases where using traditional methods are not safe or possible for certain patients. This method may work by lowering shock impedance and increasing the shock tissue surface area.

Propofol dose and efficacy of defibrillation testing during implantation of subcutaneous implantable cardioverter-defibrillators: A retrospective, single center cohort study

INTRODUCTION

Defibrillation testing (DFT) is recommended during subcutaneous implantable cardioverter-defibrillator (S-ICD) implantation. Previous studies analyzing the potential interference of propofol with defibrillation threshold are inconsistent. The purpose of this study was to analyze whether propofol affects DFT post S-ICD placement.

METHODS

All patients with S-ICD implantation between 01/2017 and 11/2020 at the University Heart Center Freiburg were retrospectively analyzed. Two groups were generated depending on the success of the first shock during DFT. Implantation characteristics and dose of anesthetics were analyzed.

RESULTS

In 12 of the included 80 (15%) patients, first shock during DFT failed. The absolute dose of propofol was significantly higher in patients with first shock failure (median 653 mg [IQR 503-855]) compared to patients with first shock termination (376 mg [200-600]; p = 0.027). Doses of opioids and midazolam as well as type of anesthesia did not differ between the groups. A multivariable binary logistic regression analysis confirmed an independent association of first shock termination and propofol dose (per 100 mg: OR 0.73 (95% CI: 0.56-0.95); p = 0.021).

CONCLUSION

There is an independent association of propofol dose and first shock failure in routine S-ICD defibrillation testing.

High Defibrillation Threshold: Brace For Impact

Sudden cardiac death (SCD) constitutes a major public health problem and accounts for approximately 50% of all cardiovascular deaths This article is protected by copyright. All rights reserved.

Successful treatment of prolonged refractory ventricular fibrillation in an anesthetized dog

OBJECTIVE

To describe a case of successful return of spontaneous circulation in an anesthetized dog that developed spontaneous ventricular fibrillation during CPR that was refractory to multiple defibrillation attempts by utilizing pharmacological antiarrhythmic therapy.

CASE SUMMARY

Cardiopulmonary arrest occurred during surgical preparation in a 1-year-old German Shepherd Dog under general anesthesia for fluoroscopic implantation of an Amplatz canine duct occluder for treatment of a patent ductus arteriosus. Pulseless electrical activity was initially diagnosed, and resuscitative efforts were immediately initiated, including basic cardiac life support, discontinuation of anesthesia with administration of reversal agents, and low-dose epinephrine administration (0.01 mg/kg, IV). After 10 minutes of CPR, the patient developed ventricular fibrillation and single-dose monophasic defibrillation attempts of escalating energy were performed. Despite these efforts, return of spontaneous circulation was unable to be achieved. However, administration of magnesium sulfate (20 mg/kg, IV) along with an additional single monophasic defibrillation attempt was successful in achieving return of spontaneous circulation.

NEW OR UNIQUE INFORMATION PROVIDED

Under current advanced cardiac life support guidelines, the best resuscitation strategy for refractory ventricular fibrillation, in which the arrhythmia persists despite multiple defibrillation attempts, remains unclear. This is especially true for veterinary patients, where refractory ventricular fibrillation is an uncommon cardiac arrest rhythm. Although guidelines for the use of antiarrhythmic therapy during cardiac arrest are well established in human medicine, evidence-based guidelines to support best practices in companion animals do not exist due to sparse data gathered through experimental studies. Only a few case reports describe successful return of spontaneous circulation following prolonged ventricular fibrillation in clinical veterinary patients. Although the use of magnesium sulfate as an antiarrhythmic agent during refractory ventricular fibrillation has been previously reported in people, this is the first case to our knowledge of refractory ventricular fibrillation in a dog that responded to magnesium sulfate.

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.

Clinical and electrocorticographic response to antiepileptic drugs in patients treated with responsive stimulation

OBJECTIVE

The objective of this study was to explore whether chronic electrocorticographic (ECoG) data recorded by a responsive neurostimulation system could be used to assess clinical responses to antiepileptic drugs (AEDs).

METHODS

Antiepileptic drugs initiated and maintained for ≥3 months by patients participating in clinical trials of the RNS^® System were identified. Such "AED Starts" that produced an additional ≥50% reduction in patient-reported clinical seizure frequency were categorized as clinically beneficial, and the remaining as not beneficial. Electrocorticographic features recorded by the RNS^® Neurostimulator were analyzed during three periods: 3 months before the AED Start, first month after the AED Start, and the first 3 months after the AED Start.

RESULTS

The most commonly added medications were clobazam (n = 41), lacosamide (n = 96), levetiracetam (n = 31), and pregabalin (n = 25). Across all four medications, there were sufficient clinical data for 193 AED Starts to be included in the analyses, and 59 AED Starts were considered clinically beneficial. The proportion of AED Starts that qualified as clinically beneficial was higher for clobazam (53.7%) and levetiracetam (51.6%) than for lacosamide (18.8%) and pregabalin (12%). Across all AED Starts for which RNS ECoG detection settings were held constant, the clinically beneficial AED Starts were associated with a significantly greater reduction in the detection of epileptiform activity (p < 0.001) at 1 (n = 33) and 3 months (n = 30) compared with AED Starts that were not beneficial at 1 (n = 71) and 3 months (n = 60). Furthermore, there was a significant reduction in interictal spike rate and spectral power (1-125 Hz) associated with a clinically beneficial response to an AED Start at 1 (n = 32) and 3 months (n = 35) (p < 0.001). These reductions were not observed at either 1 (n = 59) or 3 months (n = 60) for AED Starts that were not clinically beneficial.

CONCLUSIONS

Significant quantitative changes in ECoG data recorded by the RNS System were observed in patients who experienced an additional clinical response to a new AED. While there was variability across patients in the changes observed, the results suggest that quantitative ECoG data may provide useful information when assessing whether a patient may have a favorable clinical response to an AED.

The Selective Late Sodium Current Inhibitor Eleclazine, Unlike Amiodarone, Does Not Alter Defibrillation Threshold or Dominant Frequency of Ventricular Fibrillation

INTRODUCTION

We examined the effects of the selective late INa inhibitor eleclazine on the 50% probability of successful defibrillation (DFT50) before and after administration of amiodarone to determine its suitability for use in patients with implantable cardioverter defibrillators (ICDs).

METHODS AND RESULTS

In 20 anesthetized pigs, transvenous active-fixation cardiac defibrillation leads were fluoroscopically positioned into right ventricular apex through jugular vein. ICDs were implanted subcutaneously. Dominant frequency of ventricular fibrillation was analyzed by fast Fourier transform. The measurements were made before drug administration (control), and at 40 minutes after vehicle, eleclazine (2 mg/kg, i.v., bolus over 15 minutes), or subsequent/single amiodarone administration (10 mg/kg, i.v., bolus over 10 minutes). Eleclazine did not alter DFT50, dominant frequency, heart rate, or mean arterial pressure (MAP). Subsequent amiodarone increased DFT50 (P = 0.006), decreased dominant frequency (P = 0.022), and reduced heart rate (P = 0.031) with no change in MAP. Amiodarone alone increased DFT50 (P = 0.005; NS compared to following eleclazine) and decreased dominant frequency (P = 0.003; NS compared to following eleclazine).

CONCLUSION

Selective late INa inhibition with eleclazine does not alter DFT50 or dominant frequency of ventricular fibrillation when administered alone or in combination with amiodarone. Accordingly, eleclazine would not be anticipated to affect the margin of defibrillation safety in patients with ICDs.

Antiarrhythmic Drug Therapy to Avoid Implantable Cardioverter Defibrillator Shocks

Implantable cardioverter defibrillators (ICDs) are effective in the prevention of arrhythmic sudden cardiac death. Many patients receiving an ICD are affected by heart failure and are at risk of ventricular arrhythmias, which may lead to appropriate shocks. On the other hand, in this population the incidence of atrial fibrillation, giving rise to inappropriate ICD shocks, is high. Accordingly, ICD discharges occur frequently and many patients with an ICD will need concomitant antiarrhythmic drug therapy to avoid or reduce the frequency of shocks. Therapeutic agents such as β-blockers, class I or class III antiarrhythmic drugs effectively suppress arrhythmias, but may have side-effects. Some drugs could eventually influence the function of ICDs by altering defibrillation or pacing threshold. Few prospective randomised trials are available, but current data suggest that amiodarone is most effective for prevention of appropriate or inappropriate ICD shocks. This review article summarises current knowledge regarding the antiarrhythmic management of patients with ICDs.

Basic Cardiac Electrophysiology and Common Drug-induced Arrhythmias

Drugs can be a double-edged sword, providing the benefit of symptom alleviation and disease modification but potentially causing harm from adverse cardiac arrhythmic events. Proarrhythmia is the ability of a drug to cause an arrhythmia, the number one reason for drugs to be withdrawn from the patient. Drug-induced arrhythmias are defined as the production of de novo arrhythmias or aggravation of existing arrhythmias, as a result of previous or concomitant pharmacologic treatment. This review summarizes normal cardiac cell and tissue functioning and provides an overview of drugs that effect cardiac repolarization and the adverse effects of commonly administered antiarrhythmics.

Management of pace-terminated ventricular arrhythmias

An implantable-cardioverter defibrillator (ICD) can terminate ventricular arrhythmias by delivering a shock or by antitachycardia pacing (ATP). The ATP works by capturing the excitable gap and disrupting re-entrant ventricular arrhythmias. Multiple studies have demonstrated that ATP is successful at terminating ventricular tachycardia (VT). Shocks from the ICD are associated with higher mortality. The data are conflicting about whether appropriate ATP is associated with higher mortality. In a patient with VT that is treated by ATP, the patient's guideline-based heart failure medications should be maximized. The use of VT ablation after appropriate and successful ATP requires additional studies.

Quinoline-2-carboimine copper complex immobilized on amine functionalized silica coated magnetite nanoparticles: a novel and magnetically retrievable catalyst for the synthesis of carbamates via C–H activation of formamides

A novel and magnetically recoverable nanocatalytic system consisting of a magnetic silica based copper complex has been fabricated and applied in the synthesis of carbamates via C–H activation of formamides.

PdCl2 catalyzed efficient assembly of organic azides, CO, and alcohols under mild conditions: a direct approach to synthesize carbamates

A simple and readily available PdCl2 catalyzed carbamate synthesis method via isocyanate generation and application in situ has been developed. This chemistry provides an efficient and practical approach to synthesize carbamates from simple organic azides, CO atmosphere and alcohols. The broad scope, mild and neutral conditions, and only N2 as the byproduct make this transformation very useful. Moreover, simple examples of modification of bioactive molecules and construction of macrocycles were achieved through this protocol.

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.

Autonomic boundary conditions for ventricular fibrillation and their implications for a novel defibrillation technique

The sympathetic and parasympathetic divisions of the autonomic nervous system modulate cardiac rhythm and the probability of arrhythmia occurrence. Both increased sympathetic drive and hypoxia increase the likelihood for ventricular fibrillation (VF). Vagus nerve stimulation (VNS) can protect from fatal arrhythmias via cholinergic and nitrergic action. We sought to determine boundary conditions for VF and defibrillation by autonomic manipulations accompanied or not by hypoxic changes in urethane-anesthetized rats. VF was induced with (1) vagotomy, (2) systemic high-dose (>15 mg/kg) isoproterenol, and (3) hypoxemia. When VNS (50 Hz) produced cardiac standstill, it converted every VF episode (59/59). A nitric oxide synthase inhibitor did not reduce VNS efficacy (13/14 episodes converted), but addition of atropine reduced VNS efficacy (11/27 episodes converted). VF can be induced by autonomic derangements only under constrained conditions, including sympathetic over-activation, reduced parasympathetic input, and hypoxemia. VNS can provide an alternative method to defibrillate via its cholinergic action.

Chronic oral amiodarone but not dronedarone therapy increases ventricular defibrillation threshold during acute myocardial ischemia in a closed-chest animal model

Dronedarone, a recently approved antiarrhythmic drug, has been shown to have fewer side effects than amiodarone, particularly with regard to thyroid and neurologic events. Since the effects of either drug on ventricular defibrillation threshold during ischemia are unknown, the aim of this study was to compare the effects of dronedarone and amiodarone on defibrillation efficacy during ischemia in a closed-chest animal model. Dronedarone (30 mg·kg·d) and amiodarone (20 mg·kg·d) were administered orally for 3 weeks to 19 and 21 pigs, respectively. A control group (no treatment) comprised 19 pigs. A 2-lead endovascular defibrillation system was used. Each biphasic shock was delivered after 8 seconds of ventricular fibrillation. A step-up/step-down protocol was used to calculate mean defibrillation threshold before and 10 minutes after coronary artery occlusion using an angioplasty balloon in the left descending artery. At basal state, defibrillation threshold did not differ between the control (20.8 ± 4.8 J), amiodarone (21.2 ± 2 J), and dronedarone (19.5 ± 3 J) groups. After ischemia, the amiodarone group had a significantly higher defibrillation threshold than the control group (29.6 ± 3 J vs. 21.8 ± 5 J, respectively; P = 0.015), but the dronedarone (22.8 ± 4 J) and control groups had similar defibrillation threshold values. These data indicate that oral dronedarone treatment, unlike oral amiodarone, does not affect defibrillation threshold during ischemia in pigs.

Mitochondrial basis of the anti-arrhythmic action of lidocaine and modulation by the n-6 to n-3 PUFA ratio of cardiac phospholipids

The aim of this study was to evaluate the involvement of mitochondria in the mechanism of the anti-arrhythmic lidocaine. Rats were fed with a diet containing either n-6 polyunsaturated fatty acids (PUFAs, SSO group) or an equimolecular mixture of n-3 and n-6 PUFAs (FO group) for 8 weeks. The hearts were perfused according to the working mode using a medium with or without lidocaine 5 μm. They were then subjected to local ischemia (20 min) and reperfusion (30 min). Dietary n-3 PUFAs triggered the expected decrease in the n-6/n-3 PUFA ratio of cardiac phospholipids. Reperfusing the ischemic area favored the incidence of severe arrhythmias. Lidocaine treatment abolished almost completely reperfusion arrhythmias in the FO group, but did not display anti-arrhythmic properties in the SSO group. As it was indicated by measurements of the mitochondrial function, lidocaine seemed to favor mitochondrial calcium retention in the FO group, which might prevent cytosolic calcium spikes and reperfusion arrhythmias. In the SSO group, the resistance to lidocaine was associated with an aggravation of cellular damages. The mitochondrial calcium retention capacities were saturated, and lidocaine was unable to increase them, making the drug inefficient in preventing reperfusion arrhythmias.

Evaluation of defibrillation safety margin in modern implantable cardioverter defibrillators after administration of amiodarone

AIM

The adjunctive medication with amiodarone plays a major role in patients with an implantable cardioverter defibrillator (ICD). Amiodarone as class III antiarrhythmic drug may significantly alter the defibrillation threshold (DFT). Conflicting results exist on the clinical relevance of a DFT rise on amiodarone. The only prospective study on this issue included only a small number of patients on amiodarone. The purpose of this study was to assess the safety and clinical relevance of repeat defibrillator testing after initiation of amiodarone in modern defibrillator systems.

METHODS AND RESULTS

We assessed risks and clinical consequences of retesting defibrillation safety margin after initiation of amiodarone in 130 consecutive patients. All patients underwent intraoperative testing at the time of first ICD implantation. A repeated VF induction and defibrillator test (by protocol with a single shock and 10 J safety margin) after a total dose of at least 10 g amiodarone 4-6 weeks after initiation of medication was performed. DFT testing after initiation of amiodarone was safe as there were no complications that led to a prolonged hospital stay. In 4 of 114 patients with a left-sided device (1.6%) and 3 of 7 patients with a right-sided device (42.8%), a 10 J safety margin could not be achieved. As a result 4 patients (3.1% of study collective) had a revision of the system.

CONCLUSION

Repeat defibrillation testing after administration of amiodarone therapy rarely fails in patients with left-sided devices. We observed a higher test failure in patients with a device in the right-subpectoral position although this subgroup was small. Repeat defibrillator testing is safe as no relevant complications were observed.

Vernakalant selectively prolongs atrial refractoriness with no effect on ventricular refractoriness or defibrillation threshold in pigs

Vernakalant is a novel antiarrhythmic agent that has demonstrated clinical efficacy for the treatment of atrial fibrillation. Vernakalant blocks, to various degrees, cardiac sodium and potassium channels with a pattern that suggests atrial selectivity. We hypothesized, therefore, that vernakalant would affect atrial more than ventricular effective refractory period (ERP) and have little or no effect on ventricular defibrillation threshold (DFT). Atrial and ventricular ERP and ventricular DFT were determined before and after treatment with vernakalant or vehicle in 23 anesthetized male mixed-breed pigs. Vernakalant was infused at a rate designed to achieve stable plasma levels similar to those in human clinical trials. Atrial and ventricular ERP were determined by endocardial extrastimuli delivered to the right atria or right ventricle. Defibrillation was achieved using external biphasic shocks delivered through adhesive defibrillation patches placed on the thorax after 10 seconds of electrically induced ventricular fibrillation. The DFT was estimated using the Dixon "up-and-down" method. Vernakalant significantly increased atrial ERP compared with vehicle controls (34 ± 8 versus 9 ± 7 msec, respectively) without significantly affecting ventricular ERP or DFT. This is consistent with atrial selective actions and supports the conclusion that vernakalant does not alter the efficacy of electrical defibrillation.

Effect of substance abuse on defibrillation threshold in patients with implantable cardioverter-defibrillator

BACKGROUND

The use of recreational drugs has been observed to have deleterious effects on the heart. The aim of our study was to evaluate the effect of substance abuse on the defibrillation threshold (DFT) in patients with implantable cardioverter-defibrillators (ICDs).

METHODS

A retrospective analysis was conducted on patients who had undergone ICD placement at a tertiary university medical center in Detroit, Michigan. Subjects were identified based on self-reported drug use and placed into one of the three groups: controls, cocaine, and other illicit drugs. Due to a disparity in race among groups, the main analysis on DFT value was conducted on African-American patients only. Furthermore, exploratory analyses were conducted to investigate the effects of marijuana use and race on DFT values.

RESULTS

A history of cocaine use (n = 17) significantly increases DFT among African Americans (17.3 ± 8 Joule [J] vs 12.5 ± 5 J in cases vs controls, P < 0.05), while previous use of marijuana does not significantly influence DFT. African-American patients with a history of illicit drug use had indications for ICD implantation at an earlier age and that within the control (nondrug using) group; African Americans (n = 73) had higher DFT compared to Caucasians (n = 32), (14.5 ± 0.5 J vs 9.7 ± 0.6 J, P < 0.05).

CONCLUSIONS

A history of cocaine use in African Americans with ICD is a risk factor for high DFT and race itself (being African American) may be a risk for high DFT. Use of high-energy ICDs and other DFT lowering techniques may be considered for patients who have used or continue to use cocaine or in whom DFT testing cannot be performed at the time of implantation.

Nifekalant versus lidocaine for in-hospital shock-resistant ventricular fibrillation or tachycardia

OBJECTIVE

To compare the efficacy and safety of nifekalant, a pure class III anti-arrhythmic drug, and lidocaine in patients with shock-resistant in-hospital ventricular fibrillation (VF) or ventricular tachycardia (VT).

PATIENTS AND METHODS

Between August 2005 and March 2008, we conducted a prospective, two-arm, cluster observational study, in which participating hospitals were pre-registered either to the nifekalant arm or the lidocaine arm. Patients were enrolled if they had in-hospital VF or VT resistant to at least two defibrillation shocks. Congenital or drug-induced long QT syndrome was excluded. The primary end-point was termination of VF or VT with/without additional shock. The secondary end-points were return of spontaneous circulation (ROSC), 1-month survival and survival to hospital discharge. We also assessed the frequency of adverse events, including asystole, pulseless electrical activity and torsade de pointes.

RESULTS

In total, 55 patients were enrolled. After nifekalant, 22 of 27 patients showed termination of VF or VT, as compared with 15 of 28 patients treated with lidocaine with/without additional shock (odds ratio (OR): 3.8; 95% confidence interval (CI): 1.1-13.0; P=0.03). Twenty-three of 27 patients given nifekalant showed ROSC, as compared with 15 of 28 patients given lidocaine (OR: 5.0; 95% CI: 1.4-18.2; P=0.01). There was no difference in 1-month survival or survival to hospital discharge between the nifekalant and lidocaine arms. There was a higher incidence of asystole with lidocaine (7 of 28 patients) than with nifekalant (0 of 27 patients) (P=0.005). Torsade de pointes was not observed.

CONCLUSION

Nifekalant was more effective than lidocaine for termination of arrhythmia and for ROSC in patients with shock-resistant in-hospital VF or VT (umin-CTR No. UMIN 000001781).

[Efficacy of procainamide in the treatment of refractory ventricular fibrillation: report of 4 cases and a review of the literature]

Ventricular fibrillation is the most common malignant arrhythmia, found in up to 55% of patients who go on to experience cardiac arrest. Only monophasic or biphasic defibrillation has been shown to be effective. The efficacy of antiarrhythmic drugs is much lower and depends on how much time has elapsed since the onset of symptoms. In patients with persistent ventricular fibrillation refractory to shocks, treatment options are limited. We report 4 cases in which procainamide was administered at a dosage of 17 mg/kg in 1 minute. Heart rhythm was restored and pulse rate recovered in less than 3 minutes in all cases.