Defibrillation Threshold Testing for Right-sided Device Implants: A Review to Inform Shared Decision-making, in Association with the British Heart Rhythm Society

Prevention of sudden death using ICDs requires the reliable delivery of a high-energy shock to successfully terminate VF. Until more recently, the device implant procedure included conducting defibrillation threshold (DFT) testing involving VF induction and shock delivery to ensure efficacy. Large clinical trials, including SIMPLE and NORDIC ICD, have subsequently demonstrated that this is unnecessary, with a practice of omitting DFT testing having no impact on subsequent clinical outcomes. However, these studies specifically excluded patients requiring devices implanted on the right side, in whom the shock vector is significantly different and smaller studies suggest a higher DFT. In this review, the data regarding the use of DFT testing, focusing on right-sided implants, and the results of a survey of current UK practice are presented. In addition, a strategy of shared decision-making when it comes to deciding on the use of DFT testing during right-sided ICD implant procedures is proposed.

Accuracy of AF burden detection with the new Confirm Rx with Sharp-sense technology

Funding Acknowledgements

Type of funding sources: None.

Introduction

Implantable cardiac monitors (ICMs) are increasingly used to monitor atrial fibrillation (AF) burden following catheter ablation. AF burden recorded by the Confirm Rx™ ICM cannot be modified even after adjudication of false-positive (FP) episodes. We sought to investigate accuracy of the AF burden detection in a UK cohort.

Methods

This multicentre retrospective study included patients with Confirm Rx™ and at least one episode >6 minutes across 9 UK hospitals. Each episode had a corresponding 120-second EGM (electrogram) and heart rate scatterplot which was considered representative of the whole episode. One cardiologist adjudicated all EGMs as ‘True AF’ or ‘False positive’ and a random sample of 10% was reviewed to account for intra and interobserver variability. AF burden was computed as the duration of all episodes classified as AF by the Confirm-Rx divided by the total duration of follow-up. ‘True-AF’ burden was calculated by dividing the duration of episodes adjudicated as ‘True-AF’ by the total duration of follow-up. We also investigated the accuracy of AF burden according to implantation indication and episode duration.

Results

A total of 16,230 individual AF episodes were included from 232 consecutive patients. Overall, 26,137 hours of AF were recorded and a total follow-up 315 patient-years which equates to an AF burden of 0.95%. However, only 24,404.7 (93.3%) hours represented time in ‘True-AF’ and a ‘True-AF’ burden for the whole cohort of 0.89% (Table 1). Patients with a Confirm-Rx™ for palpitations and suspected AF had the lowest proportion of ‘True-AF’ burden and had a modest contribution to the overall AF burden (Figure 1). Conversely, patients with known AF had the highest proportion of ‘True-AF’ burden recorded. Most AF (84.5%) episodes lasted less than 1 hour with approximately a quarter adjudicated as false-positive detections, but their contribution towards overall AF burden was very small (Figure 2A-2B). In contrast, AF >3 hours accounted for 76.4% of time in AF and the proportion of ‘True-AF’ burden was 98.5%.

Conclusion

The accuracy of the estimated AF burden for the whole cohort was excellent (93.3%), driven by the high proportion of ‘True-AF’ burden in AF>3 hours.

Establishing safe, effective ablation in the diseased human ventricle: an analysis of generator impedance and electrogram attenuation

Funding Acknowledgements

Type of funding sources: Private company. Main funding source(s): Biosense Webster Inc

Background

Predictors of effective and safe lesion delivery in the human left ventricle have not been established. Generator impedance (GI) drop and electrogram (EGM) attenuation are indices which can be used as surrogates for ablation lesion parameters. Tissue pops are a complication of myocardial overheating preceded by a rise in GI and can have adverse consequences.

Purpose

To establish the relationships between Ablation Index (AI), Force Time Integral (FTI) and contact force with GI and EGM attenuation. To establish factors early in ablation that are predictive of a GI rise.

Methods

Patients undergoing ventricular tachycardia ablation were recruited. All ablations were performed with contact force sensing surround flow catheters. Electrograms were collected pre and post ablation, with GI, AI, FTI measured during. Ablations were divided into low (LVM, < 0.50mV), intermediate (IVM, 0.51 – 1.50mV) and normal voltage (NVM, > 1.50mV) based upon pre-ablation bipolar EGM amplitude. Ablations with a 5% rise in GI from maximal drop were noted and predictors of this explored.

Results

In 15 patients, 402 ablations were analysed. Filtered percentage GI drop correlated with AI and FTI, (p < 0.0005, Spearman’s ρ = 0.522 and 0.524) and reached a plateau at 763AI and 713gs, a filtered GI drop of 7.5% (Figure 1). Shallower curves occurred progressively from NVM to IVM to LVM, (p < 0.0005), (Figure 2)

The bipolar EGM significantly attenuated with ablation, (median attenuation 0.14mV, [29.3%], p <0.0005), but percentage attenuation did not correlate with AI or FTI.

Parameters associated with a GI rise during ablation were greater mean CF to maximum GI drop, (p = 0.002), greater initial percentage GI drop at 5 seconds, (p < 0.0005), power of 50W (p = 0.005), and perpendicular orientation, (p = 0.006). Percentage GI drop at 5 seconds was the best predictor of ablations with a GI rise, (AUCROC 0.773; 95% CI 0.708 – 0.838; optimal cut-off 2.44%). Mean contact force to maximum GI drop was a poor predictor of a GI rise (AUCROC 0.647; 95% CI 0.577 – 0.718, optimal cut-off 14.7g).

Conclusion

During left ventricular ablation, AI of 763 and FTI of 713gs should be targeted, with a lower impedance drop observed for more scarred myocardium. A GI drop of <2.5% at 5 seconds and contact force < 15g should be used to optimise ablation safety.

Diagnostic accuracy of the Confirm-Rx atrial fibrillation detection algorithm in real-world patients

Funding Acknowledgements

Type of funding sources: None.

Introduction

Continuous rhythm monitoring with implantable cardiac monitors (ICMs) is commonly used to detect and characterise atrial fibrillation (AF) episodes. The Confirm Rx™ with SharpSense™ technology offers four new discriminators and second pass analysis aimed at enhancing detection and improving accuracy for cardiac arrhythmias. This study sought to investigate the diagnostic accuracy of the Confirm Rx™ AF detection algorithm in a UK cohort of ‘real-world’ patients.

Methods

This multicentre retrospective study included patients with Confirm Rx™ and at least one episode of AF>6 minutes from August 2018 to August 2021 across 9 UK hospitals. Each episode had a corresponding 120-second electrogram (EGM) and heart rate scatterplot. One cardiologist manually adjudicated all EGMs as ‘True-AF’ or ‘False-positive. To assess for intra and inter-observer variability, 10% of the EGMs were reviewed. Diagnostic accuracy was determined by calculating the raw and patient-averaged positive predictive value (PPV) for AF episode of different durations and implant indications.

Results

During the study 232 patients met inclusion criteria with a total of 315 patient-years of follow-up. 16,320 individual AF episodes were adjudicated; intra- and interobserver variability was excellent (Cohen’s kappa 0.85 and 0.86, respectively). The rate of ‘True-AF’ detection was 3.19 episodes per month corresponding to a raw PPV of 74.5% for the whole cohort. The highest number of episodes per months was observed in patients with a Confirm-Rx for palpitations (5.1) and suspected AF (5.8) but only approximately half of these represented ‘True-AF’ episodes (Figure 1). Patients with known AF had the lowest rate of AF episodes (1.6 episodes per month) but the highest proportion of ‘True-AF’ episodes (PPV of 95.5%). A clear trend of improving diagnostic accuracy was seen with longer AF episodes (Table1). AF>3 hours had a PPV above 94% and all episodes lasting longer than 24 hours were ‘True-AF’. For AF episode of short duration, the PPV varied with the population being monitored; however, for longer AF episodes the PPV increased significantly and irrespective of implant indication (Figure 2).

Conclusion

Overall, the Confirm Rx™ ICM diagnostic accuracy was modest for all AF episodes lasting longer than 6 minutes (74.5%) but improved considerably for longer AF episodes irrespective of implant indication.

Keeping up appearances: the radiographic evolution of cardiovascular implantable electronic devices

In recent years, there has been a significant evolution in the field of cardiovascular implantable electronic devices (CIEDs). Pacemakers can now be leadless, implantable cardioverter defibrillators can be entirely subcutaneous and implantable loop recorders have become miniaturized. Driven by technological advances and an ageing population implant numbers have also steadily increased. These highly prevalent systems are all radio-opaque and are frequently observed on chest radiographs, yet the devices are neither well recognized nor understood. We present a pictorial review of CIEDs; describing the chest radiograph appearances of both newer generation systems and their traditional predecessors. Furthermore, we discuss the clinical role of chest radiography in both CIED implantation and follow up, with the aim of improving understanding in this important and expanding field. Finally, we present a collection of interesting and challenging radiographs, where multiple CIED systems have been implanted.

Non-contact mapping guided cardiac resynchronization therapy for a failing systemic right ventricle

AIMS

Progressive systemic right ventricular (sRV) dysfunction, atrial and ventricular arrhythmias and sudden cardiac death are well-recognized late sequelae of atrial redirection surgery in which the right ventricle is left connected to the systemic circulation. Although cardiac resynchronization therapy (CRT) poses an attractive therapeutic option, little is known about indications, patient selection, and technical aspects of best lead placement.

METHODS AND RESULTS

We undertook CRT in a 27-year-old female patient post-Mustard correction for d-transposition (d-TGA) with New York Heart Association (NYHA) grade III disability with QRS duration measuring 130 ms. There was also echocardiographic (TTE) evidence of severe sRV dysfunction. Non-contact mapping (NCM) was used to define sites of late activation within the sRV and the acute intra-arterial blood pressure (BP) response was assessed during implantation of a 4 french (F) lead onto the endocardial surface of the sRV. At 4 weeks post-implant sRV lateral wall motion had improved and the ejection fraction (EF) rose from 23 to 33%. The patient has been successfully anticoagulated and improved to NYHA II status after 6 months.

CONCLUSION

The use of NCM proved safe and effective and provided a qualitative assessment of electrical viability of the sRV complimenting the measurement of mechanical function provided by TTE. The favourable clinical response in the above case justifies a prospective evaluation of this strategy.

Cardiac defibrillation therapy for at risk patients with systemic right ventricular dysfunction secondary to atrial redirection surgery for dextro-transposition of the great arteries

AIM

To review techniques of implantable cardioverter-defibrillators (ICD) in patients after Mustard surgery for arterial transposition.

METHODS AND RESULTS

Retrospective analysis of all Mustard patients receiving ICDs at our institution. Five patients (median age 24 years, range 19-35, 3 male) with systemic right ventricular dysfunction (sRV) dysfunction and New York Heart Association (NYHA) II and III, received ICDs. Implantation was performed transvenously in three patients, epicardial patches and subcutaneous arrays at surgery in two patients. Two patients required lead extraction and baffle stent angioplasty before ICD implantation. Defibrillation vectors incorporating the anterior sRV mass [i.e., sub-pulmonary left ventricle (pLV) to generator can, and between epicardial defibrillator patches], consistently achieved a minimum 10 joule(J) safety margin during defibrillation threshold (DFT) testing. Subcutaneous arrays and endocardial vectors that included a superior vena cava (SVC) electrode were less effective. One patient developed pulmonary oedema post-procedure. At a median 20 months, all patients were alive and in NYHA class II. Follow-up over 24 months documented multiple non-sustained ventricular tachycardia (VT) in the group and one patient had recurrent VT with aborted device therapy.

CONCLUSION

Defibrillator implantation in Mustard patients is challenging. Sub-optimal defibrillation should be anticipated and can be overcome using vectors which integrate the RV mass and high-energy devices. A staged procedure involving pre-implant interventions or separate DFT tests, where indicated, may be better tolerated by patients.

What is the role for revascularisation in patients being considered for ICD therapy?

Patients being considered for ICD therapy are a heterogeneous group.For the vast majority, who have significant left ventricular impairment, it has become common practice to assess their coronary artery anatomy as a surrogate for ischaemia and/or viability. Such patients are therefore frequently under the care of both electrophysiologists and interventionists. The coronary anatomy often raises the dilemma about whether such patients should undergo revascularisation. If the patients present with angina or in the context of an acute myocardial infarct then this decision is clear cut. By contrast, however, a significant proportion of them have no history to suggest ongoing ischaemia or of recent MI. In conventional practice, therefore, there would be no decisive mandate to offer them revascularisation, especially PCI, in the absence of further objective evidence of ischaemia or viability. A review of the literature in our paper does not resolve this dilemma.Further observational data are required to help guide cardiologists as to which of these patients will benefit from revascularisation, since in many cases the coronary anatomy is no surrogate for the presence of ischaemia or viability.

Passive electrode effect reduces defibrillation threshold in bi-filament middle cardiac vein defibrillation

AIMS

To investigate whether a passive electrode effect decreases defibrillation threshold (DFT) in multi-filament middle cardiac vein (MCV) defibrillation.

METHODS AND RESULTS

Twelve pigs underwent active housing (AH) insertion, with defibrillation coils placed transvenously in right ventricular apex and superior vena cava. The MCV was cannulated, and 1.12F, 50 mm coil electrodes (Ela Medical SA, France) were deployed in its right and left branches. Lead placement was possible in 11 of 12 animals. DFT (J, mean +/- SD) was determined by three-reversal binary search and compared between the MCV monofilament (single filament deployed) and the AH (25.9 +/- 10.9) and the MCV mono + passive filaments (both filaments deployed, one connected) and the AH (19.9 +/- 11.4); 24% DFT reduction P = 0.008.

CONCLUSION

A bystander electrode adjacent to a monofilament electrode in the MCV reduces DFT by 24% when compared with monofilament MCV alone. Microfilament electrodes decrease DFT as auxiliary anode but not as sole anode.

Radiation peak skin dose to risk stratify electrophysiological procedures for deterministic skin damage

Ionising radiation is has the potential to cause harm both by increasing the probability future malignancy (stochastic mechanisms) and by direct physical injury (deterministic mechanisms). Several measures have been developed to quantify radiation exposure during a procedure and cardiologists usually refer to fluoroscopic screening time (FST). FST, however, has limitations for predicting deterministic injury which is directly dependant on peak skin dose (PSD). We compared FST to PSD for a range of interventional cardiac electrophysiology procedures.

METHODS

All patients undergoing electrophysiology procedures during a 2-month period in our institution were studied. Demographic details, nature of procedure, FST and PSD were measured. The FST to PSD ratio was calculated and compared between patient and procedural factors.

RESULTS

67 procedures on patients (23 female) with body mass index (BMI) of 28 (SD 5) Kg/m2 were studied. Screening times ranged from 0.2 to 96.6 min (median 11.2). PSD ranged from <0.1 to 1108 mGy (median 141). There was a positive correlation between PSD to FST ratio and BMI (r = 0.59, p < 0.001). The PSD to FST ratio was higher in cardiac resynchronization therapy (CRT) devices than single or dual chamber ICDs (p = 0.002).

CONCLUSION

FST is not a reliable predictor of deterministic skin injury and in high-risk procedures such as CRT devices and those on individuals of high BMI PSD should be measured.

Implantable loop recorders detect tachyarrhythmias in symptomatic patients with negative electrophysiological studies

BACKGROUND

Implantable loop recorders (ILR) are a valuable tool in the investigation of syncope and compare favourably with non-invasive and intracardiac electrophysiological assessment of bradycardia. They are known to detect tachyarrhythmias but have not been shown to add to the diagnostic yield of electrophysiological testing in symptomatic patients.

METHODS

We prospectively studied the first 41 patients (aged 48+/-19 years) in whom ILR were used at our institution after negative electrophysiological studies (EPS). All patients were symptomatic with palpitations (11), syncope (22) or both (8). Nine patients had known structural heart disease (two ischaemic, four cardiomyopathy, two valvular and one congenital). Patients were assessed according to demographic factors, symptoms and investigations. Loop recordings were analysed and assessed according to conventional criteria.

RESULTS

Among 41 patients in whom electrophysiological studies had failed to demonstrate arrhythmias, six were found to have clinically significant tachyarrhythmias (four ventricular and two supraventricular).

CONCLUSION

ILR diagnose prognostically significant tachyarrhythmias in symptomatic patients with negative electrophysiological studies.

Determination of Human Ventricular Repolarization by Noncontact Mapping

Background— Noncontact mapping (NCM) has not been validated as a clinical technique to measure ventricular repolarization. We used NCM to determine repolarization characteristics by analysis of reconstructed unipolar electrograms (UEs) at the same sites as monophasic action potential (MAP) recordings in the human ventricle.

Methods and Results— MAPs were recorded from a total of 355 beats at 46 sites in the left or right ventricle of 9 patients undergoing ablation of ventricular tachycardia guided by NCM (EnSite system). Measurements were made during sinus rhythm, constant right ventricular pacing, and ventricular extrastimuli during restitution-curve construction. The EnGuide locator signal was used to document MAP catheter locations on the endocardial geometry. UE-determined activation-recovery interval (ARI) measured at the maximum derivative of the T wave (Wyatt method) and the minimum derivative of the positive T wave (alternative method) was correlated with MAP measured at 90% repolarization (MAP90%) at the same sites. ARI correlated with MAP90% during steady state by the Wyatt method ( r =0.83, P <0.001) and the alternative method ( r =0.94, P <0.001). Restitution curves constructed from MAP and UE data exhibited the same characteristics, with a mean correlation coefficient of 0.95 (range, 0.90 to 0.99, P <0.001). The error between ARI and MAP90% was greater over a shorter diastolic coupling interval but was not influenced by distance of the sampling site from the multielectrode array.

Conclusions— NCM accurately determines steady-state and dynamic endocardial repolarization in humans. Global, high-density, NCM data could be used to characterize abnormalities of human ventricular repolarization.

Examination of a middle cardiac vein defibrillation coil as stand-alone anode, auxiliary anode, and bystander electrode in a transvenous defibrillation circuit

In porcine studies anodes in the middle cardiac vein compare favorably with those in the RV. It has not been demonstrated whether the RV and middle cardiac vein or the middle cardiac vein alone anodes are superior when shocking to a conventional SVC and active housing cathode nor whether a bystander middle cardiac vein electrode exerts a passive electrode affect. Twelve pigs were anesthetized and had an active housing implanted in the left pectoral region and defibrillation coils placed at the RV apex and in the SVC. A custom-made defibrillation coil (Ela Medical) was advanced into the middle cardiac vein through a 9 Fr transvenous catheter. The DFT for three anodes (RV; RV and middle cardiac vein; middle cardiac vein) to the SVC and active housing was then assessed by a three reversal binary search, the order of testing was randomized. In seven animals DFT was assessed in the same way for the configuration of RV to SVC and active housing twice more, with and without a bystander middle cardiac vein coil electrode in place. The results were middle cardiac vein 7.5 +/- 1.7 J, RV and middle cardiac vein 7.3 +/- 1.7 J reduced DFT significantly compared to RV 13.8 +/- 4.2 J (both P < 0.000). There was no significant difference between the middle cardiac vein and the middle cardiac vein and RV (P = 0.67, 95% CI for difference -0.64-0.96). The DFT of RV to SVC and the active housing was the same with (13.2 +/- 4.0) and without (13.7 +/- 4.2) the middle cardiac vein bystander coil in place (P = 0.177, 95% CI for difference -0.33-1.33 J). Shocking to a SVC and active housing cathode, middle cardiac vein, and RV and middle cardiac vein anodes are equally effective in lowering DFT compared to the RV. The middle cardiac vein coil electrode does not exert a passive electrode affect on the RV to the SVC and active housing defibrillation.

Evaluation of body weight as a predictive factor for transvenous ventricular defibrillation characteristics

AIMS

To investigate the correlation between body weight and defibrillation threshold (DFT) for transvenous lead systems using a porcine model.

METHODS AND RESULTS

Twenty-eight pigs were anaesthetised and DFTs assessed in single and dual coil configurations using a four-reversal binary search method. DFT was correlated with body weight in the RV --> Can and RV --> SVC + Can configurations. A Pearson correlation coefficient and a two-sided p-value were calculated. A positive correlation exists between body weight and DFT in RV --> Can (r=0.66, p<0.000) and RV --> SVC + Can (r=0.44, p=0.018).

CONCLUSION

There is a significant correlation between body weight and DFT in swine. This tends to be greater in the two-electrode than in the three-electrode configuration. With these and previous human observations, one may predict a higher DFT in heavy individuals and make appropriate procedural adjustments.

Comparison of coronary venous defibrillation with conventional transvenous internal defibrillation in man

OBJECTIVE

Animal studies have shown that defibrillation in coronary veins is more effective than in the right ventricle. We aimed to assess the feasibility of placing defibrillation electrodes in the middle cardiac vein (MCV) in man and its impact on defibrillation requirements.

METHODS

A prospective randomised study conducted in a tertiary referral centre. 10 patients (9 male) undergoing ICD implantation (65 (12) yrs) for NASPE/BPEG indications were studied. Defibrillation thresholds (DFT) were measured, using a binary search and an external defibrillator after 10 seconds of ventricular fibrillation, for the following configurations in each patient (order of testing randomised): RV + MCV --> Can and RV --> SVC + Can.

INTERVENTIONS

A dual coil defibrillation electrode was placed transvenously in the right ventricle (RV) in the conventional manner. Using a guiding catheter a 3.2 Fr (67.5 mm length) electrode was placed transvenously in MCV. A test-can was placed subcutaneously in the left pectoral region.

RESULTS

Lead placement was possible in 8/10 pts. Time to perform a middle cardiac venogram and place the electrode was 21 (23) mins. No adverse events were observed. Defibrillation current was less (6.7 (2.7) A) with RV + MCV --> Can compared to the conventional RV --> SVC + Can configuration (8.9 (3.4) A, p = 0.03). There was no significant difference in defibrillation voltage or energy. However, shock impedance was higher in the former configuration (57 (10) v. 43 (6) Omega, p = 0.001).

CONCLUSIONS

In the majority of cases placement of a defibrillation lead in MCV is feasible. Defibrillation current requirements are 25% less when the shock is delivered using a MCV electrode.