Minimizing Inappropriate or “Unnecessary” Implantable Cardioverter-Defibrillator Shocks

Machine learning-derived cycle length variability metrics predict spontaneously terminating ventricular tachycardia in implantable cardioverter defibrillator recipients

Aims

Implantable cardioverter defibrillator (ICD) therapies have been associated with increased mortality and should be minimized when safe to do so. We hypothesized that machine learning-derived ventricular tachycardia (VT) cycle length (CL) variability metrics could be used to discriminate between sustained and spontaneously terminating VT.

Methods and results

In this single-centre retrospective study, we analysed data from 69 VT episodes stored on ICDs from 27 patients (36 spontaneously terminating VT, 33 sustained VT). Several VT CL parameters including heart rate variability metrics were calculated. Additionally, a first order auto-regression model was fitted using the first 10 CLs. Using features derived from the first 10 CLs, a random forest classifier was used to predict VT termination. Sustained VT episodes had more stable CLs. Using data from the first 10 CLs only, there was greater CL variability in the spontaneously terminating episodes (mean of standard deviation of first 10 CLs: 20.1 ± 8.9 vs. 11.5 ± 7.8 ms, P < 0.0001). The auto-regression coefficient was significantly greater in spontaneously terminating episodes (mean auto-regression coefficient 0.39 ± 0.32 vs. 0.14 ± 0.39, P < 0.005). A random forest classifier with six features yielded an accuracy of 0.77 (95% confidence interval 0.67 to 0.87) for prediction of VT termination.

Conclusion

Ventricular tachycardia CL variability and instability are associated with spontaneously terminating VT and can be used to predict spontaneous VT termination. Given the harmful effects of unnecessary ICD shocks, this machine learning model could be incorporated into ICD algorithms to defer therapies for episodes of VT that are likely to self-terminate.

Complications related to pacemakers and other cardiac implantable electronic devices: essentials for internists and emergency physicians

With the aging population, improving technology, and expanding indications for diagnosing and treating arrhythmias and heart failure, many patients are receiving cardiac implantable electronic devices (CIEDs) such as pacemakers and implantable cardioverter defibrillators. Consequently, patients with CIEDs are frequently encountered in the emergency department and in the wards. It is imperative that emergency physicians and internists have a strong foundation on CIEDs and their potential complications. This review aims to help physicians develop a framework in approaching CIEDs and to recognize and manage clinical scenarios that may arise from CIED complications.

A Case of 25 Inappropriate Automatic Implantable Cardioverter Defibrillator Shocks and 22 Episodes of Antitachycardia Pacing

An implantable cardioverter defibrillator (ICD) can save lives from fatal tachyarrhythmias. In rare cases, these devices can fail or malfunction. We present a case of a patient that suffered from 25 inappropriate shocks and 22 episodes of antitachycardia pacing (ATP), secondary to a probable non-traumatic dual lead fracture. One episode of ATP induced an R-on-T phenomenon, causing monomorphic ventricular tachycardia in the patient. The inappropriately functioning ICD also required two magnets to be placed on the patient's chest in the emergency department to convert the device to an asynchronous mode. An unexpected case of this magnitude and in such a brief timeframe has not been reported in prior ICD studies.

Effect of Novel Programming on Inappropriate Implantable Cardioverter-Defibrillator Therapy in Patients With Very Low Ejection Fraction (from A MADIT-RIT)

The Multicenter Automatic Defibrillator Implantation Trial - Reduce Inappropriate Therapy showed a significant reduction in the risk of inappropriate therapy in patients with a programmed high-rate cutoff ≥200 beats per minute or delayed therapy for events ≥170 beats per minute compared with conventional programming. We aimed to characterize outcomes by left ventricular ejection fraction (LVEF) ranges for patients with high-rate, delayed, or conventional implantable cardioverter-defibrillator programming. We assessed the effect of LVEF (LVEF <15%, LVEF 15% to 25%, LVEF >25%) on the risk of inappropriate conventional implantable cardioverter-defibrillator therapy and death in Multicenter Automatic Defibrillator Implantation Trial - Reduce Inappropriate Therapy. Inappropriate therapies and death were independently evaluated by the adjudication committee. Statistical methods involved Kaplan-Meier time-to-event graphs and Cox proportional hazards regression analyses. The study involved 140 patients (9%) with LVEF 15%, 585 with LVEF 15% to 25% (39%), and 774 with LVEF >25% (52%). High-rate or delayed programming significantly reduced the risk of inappropriate therapy compared with conventional programming in patients with all LVEFs (p <0.001 for all LVEF). Patients with LVEF <15% had an exceptional 97% lower risk of inappropriate therapy, with high-rate programming than conventional programming (hazard ratio 0.028, p = 0.001), without an increase in mortality. High-rate and delayed programming is superior to conventional programming in all LVEF ranges, without adverse effects.

Ventricular arrhythmia management in patients with genetic cardiomyopathies

Genetic cardiomyopathies are associated with increased risk for cardiac arrhythmias and sudden cardiac death. The management of ventricular arrhythmias (VAs) in patients with these conditions can be nuanced due to particular disease-based considerations, yet data specifically addressing management in these patients are limited. Here we describe the current evidence-based approach to the management of ventricular rhythm disorders in patients with genetic forms of cardiomyopathy, namely, hypertrophic cardiomyopathy, arrhythmogenic cardiomyopathy, left ventricular noncompaction, and Brugada syndrome, including recommendations from consensus guideline statements when available.

Quantifying cardiac sympathetic denervation: first studies of 18F-fluorohydroxyphenethylguanidines in cardiomyopathy patients

PURPOSE

4-¹⁸F-Fluoro-m-hydroxyphenethylguanidine (¹⁸F-4F-MHPG) and 3-¹⁸F-fluoro-p-hydroxyphenethylguanidine (¹⁸F-3F-PHPG) were developed for quantifying regional cardiac sympathetic nerve density using tracer kinetic analysis. The aim of this study was to evaluate their performance in cardiomyopathy patients.

METHODS

Eight cardiomyopathy patients were scanned with ¹⁸F-4F-MHPG and ¹⁸F-3F-PHPG. Also, regional resting perfusion was assessed with ¹³N-ammonia. ¹⁸F-4F-MHPG and ¹⁸F-3F-PHPG kinetics were analyzed using the Patlak graphical method to obtain Patlak slopes K_p (mL/min/g) as measures of regional nerve density. Patlak slope polar maps were used to evaluate the pattern and extent of cardiac denervation. For comparison, "retention index" (RI) values (mL blood/min/mL tissue) were also calculated and used to assess denervation. Perfusion polar maps were used to estimate the extent of hypoperfusion.

RESULTS

Patlak analysis of ¹⁸F-4F-MHPG and ¹⁸F-3F-PHPG kinetics was successful in all subjects, demonstrating the robustness of this approach in cardiomyopathy patients. Substantial regional denervation was observed in all subjects, ranging from 25 to 74% of the left ventricle. Denervation zones were equal to or larger than the size of corresponding areas of hypoperfusion. The two tracers provided comparable metrics of regional nerve density and the extent of left ventricular denervation. ¹⁸F-4F-MHPG exhibited faster liver clearance than ¹⁸F-3F-PHPG, reducing spillover from the liver into the inferior wall. ¹⁸F-4F-MHPG was also metabolized more consistently in plasma, which may allow application of population-averaged metabolite corrections.

CONCLUSION

The advantages of ¹⁸F-4F-MHPG (more rapid liver clearance, more consistent metabolism in plasma) make it the better imaging agent to carry forward into future clinical studies in patients with cardiomyopathy.

TRIAL REGISTRATION

Registered at the ClinicalTrials.gov website (NCT02669563). URL: https://clinicaltrials.gov/ct2/show/NCT02669563.

A review of specialized and automated features in implantable cardiac devices

Automated features available in cardiac implantable electronic devices continue to increase in number and complexity. These features are frequently confused with device malfunction and often result in unnecessary clinical attention. This review will serve as an update to some of the more commonly-encountered features discussed in terms of the behavior they exhibit.

Inappropriate ICD shock due to hot tub-induced external electrical interference

BACKGROUND

A 72-year-old white male with a history of rapid nonsustained ventricular tachycardia, hypertrophic cardiomyopathy, and intermittent Brugada-type ECG had a single-lead implantable cardioverter-defibrillator (ICD) implantation and received a sudden ICD shock while in the hot tub. To the best of our knowledge this is the first case report of hot tub jet-induced inappropriate ICD shock.

METHODS

ICD interrogation and analysis of intracardiac electrograms and event markers.

RESULTS

ICD interrogation revealed inappropriate ICD shocks due to electrical interference of hot tub engine; 60-cycle electrical artifact mimicking fast ventricular fibrillation erroneously detected by the device. The device then delivered a 34.8 joules shock while the patient was actually in sinus rhythm.

CONCLUSIONS

Electrical interference due to external sources such as hot tub engines may occur and produce an inappropriate detection and ICD shock. Precaution and patient education is warranted.

Inappropriate ICD Discharge Related to Electrical Muscle Stimulation in Chiropractic Therapy: A Case Report

Implantable cardioverter defibrillators (ICDs) have been shown to reduce mortality in high-risk patients. Despite several advances in programming ICDs, inappropriate shocks persist and continue to be psychologically and physically disturbing. External electromagnetic interference from electrocautery, welding, acupunctures, low-output transcutaneous electric nerve stimulators, and electronic muscle stimulators may result in inappropriate ICD sensing and shock. We present a 63-year-old female who presented to the emergency department after an ICD shock while undergoing electronic muscle stimulation in chiropractic treatment, during which light electrical pulses were sent through skin electrodes. Our case highlights the importance of recognizing methods used by alternative medicine doctors, including electrical muscle stimulation that may cause electromagnetic interference and inappropriate ICD discharge and therefore, a higher overall mortality risk.

Incidence of Atrial Tachyarrhythmias in Patients With Early Repolarization Syndrome

Atrial tachyarrhythmias (ATAs) occur in a significant proportion of Brugada syndrome (BrS) patients and are often an important cause of inappropriate shocks. The aim of this retrospective study was to evaluate the incidence of ATAs and ATA-induced inappropriate shocks in early repolarization syndrome (ERS) patients as compared to BrS patients.We analyzed data from 20 consecutive patients who were diagnosed with ERS and compared them with patients diagnosed with BrS (n = 31). Clinical and ICD interrogation data were collected and analyzed for all events with ICD shocks.Three patients had a history of atrial fibrillation (AF) prior to ICD implantation. One patient had AV reentrant tachycardia and was successfully ablated before ICD implantation. ATAs were newly diagnosed in 4 patients with no prior history of AF. There were no significant differences in gender, age, or left atrial diameter between ATA development. Four (20%) of 20 consecutive patients received inappropriate ICD shocks for ATAs. One suffered from repeat inappropriate shocks triggered by paroxysmal AF and received catheter ablation for AF.ATAs were not infrequent in patients with ERS and seemed to be related to inappropriate ICD therapy. Careful ICD programming is required to reduce ATA-related inappropriate ICD shock in patients with ERS.

Effectiveness of Implantable Cardioverter-Defibrillator Therapy for Heart Failure Patients according to Ischemic or Non-Ischemic Etiology in Korea

Background and Objectives

This study was performed to describe clinical characteristics of patients with left ventriculars (LV) dysfunction and implantable cardioverter-defibrillator (ICD), and to evaluate the effect of ICD therapy on survival in Yeongnam province of Korea.

Subjects and Methods

From a community-based device registry (9 centers, Yeongnam province, from November 1999 to September 2012), 146 patients with LV dysfunction and an ICD implanted for primary or secondary prophylaxis, were analyzed. The patients were divided into two groups, based on the etiology (73 with ischemic cardiomyopathy and 73 with non-ischemic cardiomyopathy), and indication for the device implantation (36 for primary prevention and 110 for secondary prevention). The cumulative first shock rate, all cause death, and type and mode of death, were determined according to the etiology and indication.

Results

Over a mean follow-up of 3.5 years, the overall ICD shock rate was about 39.0%. ICD shock therapy was significantly more frequent in the secondary prevention group (46.4% vs. 16.7%, p=0.002). The cumulative probability of a first appropriate shock was higher in the secondary prevention group (p=0.015). There was no significant difference in the all-cause death, cardiac death, and mode of death between the groups according to the etiology and indication.

Conclusion

Studies from this multicenter regional registry data shows that in both ischemic and non-ischemic cardiomyopathy patients, the ICD shock therapy rate was higher in the secondary prevention group than primary prevention group.

Very high rate programming in primary prevention patients with reduced ejection fraction implanted with a defibrillator: Results from a large multicenter controlled study

BACKGROUND

Programming implantable cardioverter-defibrillators (ICDs) with a high-rate therapy strategy has proven to be effective in reducing shocks and is associated with a reduced mortality.

OBJECTIVE

We sought to determine the impact of a very high rate cutoff programming strategy on outcomes in patients with a primary indication for an ICD due to reduced left ventricular ejection fraction.

METHODS

Using data from the multicenter French DAI-PP registry, this cohort-controlled study compared outcomes in 500 patients programmed with a very high rate cutoff (VH-RATE group: monitor zone 170-219 beats/min; ventricular fibrillation zone ≥220 beats/min with 13 ± 4 detection intervals) with 1500 matched control patients programmed with 1 or 2 therapy zone. All ICDs were implanted for primary prevention in patients with systolic dysfunction. Risks of events were compared after propensity score matching of sex, age, ejection fraction, New York Heart Association class, cardiomyopathy, atrial fibrillation, and type of device.

RESULTS

After a mean follow-up of 3.6 ± 2.3 years, VH-RATE programming was associated with a reduction of appropriate therapy risk (hazard ratio [HR] 0.40; 95% confidence interval [CI] 0.31-0.51; P < .0001) and inappropriate shock (HR 0.42; 95% CI 0.27-0.63; P < .0001). It was also associated with a decreased risk of sudden cardiac death (HR 0.43; 95% CI 0.17-0.99; P = .04) as compared with patients programmed with 2 therapy zones. There was no significant difference in overall survival between the groups.

CONCLUSION

In patients implanted with an ICD in primary prevention with left ventricular dysfunction, very high rate cutoff programming (single therapy zone ≥220 beats/min) was associated with a 60% reduction of appropriate therapies as well as inappropriate shocks, without affecting mortality.

ICD discrimination of SVT versus VT with 1:1 V-A conduction: A review of the literature

Inappropriate ICD shocks are associated with increased mortality. They also impair patients' quality of life, increase hospitalizations, and raise health-care costs. Nearly 80% of inappropriate ICD shocks are caused by supraventricular tachycardia. Here we report the case of a patient who received a single-lead dual-chamber sensing ICD for primary prevention of sudden cardiac death and experienced inappropriate ICD shocks. V-A time, electrogram morphology, and response to antitachycardia pacing suggested atrioventricular nodal reentry tachycardia, which was confirmed in an electrophysiology study. Inspired by this case, we performed a literature review to discuss mechanisms for discrimination of supraventricular tachycardia with 1:1 A:V relationship from ventricular tachycardia with 1:1 retrograde conduction.

Low rate of and rapid attention to inappropriate ICD shocks with remote device and rhythm monitoring: a qualitative study

Objectives

Inappropriate shocks are unpleasant and painful. We hypothesise that remote monitoring and careful attention to known and incident atrial fibrillation (AF) can reduce inappropriate shocks to a very low level in clinical praxis.

Methods

Altogether 259 patients with implantable cardioverter defibrillator implanted for secondary (S, n=113) and primary (P, n=146) prevention were followed via remote monitoring. At implant, 42S (37%) and 54P (37%) patients had known AF.

Results

Inappropriate shocks, all but five due to AF, occurred in 7S (6.2%) and 11P (7.5%), and there were only inappropriate shocks in 5/7S and in 8/11P. They occurred in four of 42S (9.5%) with and in three of 71S (4.2%) without known AF, and in seven of 54P (13%) with and in four of 92P (4.3%) without known AF. The median time from shock to action was 5 and 1 day, respectively. Actions were medication with amiodarone, β blockers, β blockers+amiodarone or β blockers+digoxin (n=5), β blockers+insertion of an atrial lead (n=1), replacement of a fractured lead (n=2), reprogramming in combination with β blockers, digoxin or amiodarone (n=4), reprogramming (n=2) and none (n=4). After action, four further inappropriate shocks occurred during more than 2 years of follow-up, all due to AF.

Conclusions

Inappropriate shocks occurred at a low rate and most often because of AF known at implant. Remote monitoring enabled rapid action, after which few inappropriate shocks occurred over more than 2 years. Attention to known and incident AF was the most important action to reduce inappropriate shocks.

Implantable cardioverter-defibrillators in children

Implantable cardioverter-defibrillators (ICD) have become an integral component in the management of children with life-threatening cardiac arrhythmias complicating a variety of different inherited and congenital cardiovascular conditions. Implantation often requires novel approaches and configurations to overcome the size and anatomic limitations posed by many children needing ICDs. While their use has undoubtedly saved many lives, ICD use may be associated with significant morbidity, so detailed case selection and individualised postimplant programming is critical.

The healthcare utilization and cost of treating patients experiencing inappropriate implantable cardioverter defibrillator shocks: a propensity score study

BACKGROUND

Inappropriate shocks (IASs) from implantable cardioverter defibrillators (ICDs) are associated with decreased quality of life, but whether they increase healthcare utilization and treatment costs is unknown. We sought to determine the impact of IASs on subsequent healthcare utilization and treatment costs.

METHODS

We conducted a case-control analysis of ICD patients at a single institution from 1997 to 2010 and who had ≥12 months of post-ICD implant follow-up. Cases included all patients experiencing an IAS during the first 12 months after implantation. Eligible control patients did not receive a shock of any kind during the 12 months after implantation. Propensity scores based on 36 covariates (area under curve = 0.78) were used to match cases to controls. We compared the rate (occurrences/person year [PY]) of healthcare utilization immediately following IAS to the end of the 12-month follow-up period to the rate in the no-shock group over 12 months of follow-up. We also compared 12-month postimplant treatment (outpatient clinic, emergency room, and hospitalization) costs in both groups.

RESULTS

A total of 76 patients experiencing ≥1 IAS during the first 12 months after implant (contributing 48 PYs) were matched to 76 no-shock patients (contributing 76 PYs). Cardiovascular (CV)-related clinic visit and hospitalization rates were increased following an IAS compared to those not receiving a shock (4.0 vs 3.3 and 0.7 vs 0.5, respectively, P = 0.02 for both). CV-related emergency room visitation (0.15 vs 0.08) rates were also numerically higher following an IAS, but did not reach statistical significance (P = 0.26). Patients experiencing an IAS accrued greater treatment costs during the 12 months postimplant compared to no-shock patients ($13,973 ± $46,345 vs $6,790 ± $19,091, P = 0.001).

CONCLUSION

Recipients of IAS utilize the healthcare system more frequently following an IAS than patients not experiencing a shock. This increased utilization results in higher costs of treating IAS patients during the 12 months postimplant.

Implant-based multiparameter telemonitoring of patients with heart failure (IN-TIME): a randomised controlled trial

BACKGROUND

An increasing number of patients with heart failure receive implantable cardioverter-defibrillators (ICDs) or cardiac resynchronisation defibrillators (CRT-Ds) with telemonitoring function. Early detection of worsening heart failure, or upstream factors predisposing to worsening heart failure, by implant-based telemonitoring might enable pre-emptive intervention and improve outcomes, but the evidence is weak. We investigated this possibility in IN-TIME, a clinical trial.

METHODS

We did this randomised, controlled trial at 36 tertiary clinical centres and hospitals in Australia, Europe, and Israel. We enrolled patients with chronic heart failure, NYHA class II-III symptoms, ejection fraction of no more than 35%, optimal drug treatment, no permanent atrial fibrillation, and a recent dual-chamber ICD or CRT-D implantation. After a 1 month run-in phase, patients were randomly assigned (1:1) to either automatic, daily, implant-based, multiparameter telemonitoring in addition to standard care or standard care without telemonitoring. Investigators were not masked to treatment allocation. Patients were masked to allocation unless they were contacted because of telemonitoring findings. Follow-up was 1 year. The primary outcome measure was a composite clinical score combining all-cause death, overnight hospital admission for heart failure, change in NYHA class, and change in patient global self-assessment, for the intention-to-treat population. The trial is registered with ClinicalTrials.gov, number NCT00538356.

FINDINGS

We enrolled 716 patients, of whom 664 were randomly assigned (333 to telemonitoring, 331 to control). Mean age was 65·5 years and mean ejection fraction was 26%. 285 (43%) of patients had NYHA functional class II and 378 (57%) had NYHA class III. Most patients received CRT-Ds (390; 58·7%). At 1 year, 63 (18·9%) of 333 patients in the telemonitoring group versus 90 (27·2%) of 331 in the control group (p=0·013) had worsened composite score (odds ratio 0·63, 95% CI 0·43-0·90). Ten versus 27 patients died during follow-up.

INTERPRETATION

Automatic, daily, implant-based, multiparameter telemonitoring can significantly improve clinical outcomes for patients with heart failure. Such telemonitoring is feasible and should be used in clinical practice.

FUNDING

Biotronik SE & Co. KG.

State of the art of ICD programming: Lessons learned and future directions

The lifesaving benefits of implantable cardioverter defibrillator (ICD) therapy are more and more weighted against possible harm (e.g. unnecessary device therapy, procedural complications, device malfunction etc.) which might have adverse effects on patients' perceived health status and quality of life. Hence, there has been an increasing interest in the optimisation of ICD programming to prevent inappropriate and appropriate but unnecessary device therapy. The purpose of the current report is to give an overview of research into the optimisation of ICD programming and present the design of the on-going ENHANCED-ICD study. The ENHANCED-ICD study is a prospective, safety monitoring study enrolling 60 primary and secondary prophylactic ICD patients at the University Medical Center Utrecht. Patients implanted with any type of ICD with SmartShock technology(TM), and between 18-80 years of age, were eligible to participate. In all patients a prolonged detection of 60/80 intervals was programmed. The primary objective of the study is to investigate whether enhanced programming to further reduce ICD therapies is safe. The secondary objective is to examine the impact of enhanced programming on (i) antitachycardia pacing and shocks (both appropriate and inappropriate) and (ii) quality of life and distress. The first results of the ENHANCED-ICD study are expected in 2015.

Admittance to detect alterations in left ventricular stroke volume

BACKGROUND

Implantable cardioverter-defibrillators monitor intracardiac electrograms (EGMs) to discriminate between ventricular and supraventricular tachycardias. The incidence of inappropriate shocks remains high because of misclassification of the tachycardia in an otherwise hemodynamically stable individual. Coupling EGMs with an assessment of left ventricular (LV) stroke volume (SV) could help in gauging hemodynamics during an arrhythmia and reducing inappropriate shocks.

OBJECTIVE

The purpose of this study was to use the admittance method to accurately derive LV SV.

METHODS

Ultrasonic flow probe and LV endocardial crystals were used in canines (n = 12) as the standard for LV SV. Biventricular pacing leads were inserted to obtain admittance measurements. A tetrapolar, complex impedance measurement was made between the Bi-V leads. The real and imaginary components of impedance were used to discard the myocardial component from the blood component to derive instantaneous blood conductance (Gb). Alterations in SV were measured during right ventricular pacing, dopamine infusion, and inferior vena cava occlusion.

RESULTS

Gb tracks steady-state changes in SV more accurately than traditional magnitude (ie, |Y|, without removal of the muscle signal) during right ventricular pacing and dopamine infusion (P = .004). Instantaneous LV volume also was tracked more accurately by Gb than ∣Y∣ in the subset of subjects that underwent inferior vena cava occlusions (n = 5, P = .025). Finite element modeling demonstrates that admittance shifts more sensitivity of the measurement to the LV blood chamber as the mechanism for improvement (see Online Appendix).

CONCLUSION

Monitoring LV SV is possible using the admittance method with biventricular pacing leads. The technique could be piggybacked to complement EGMs to determine if arrhythmias are hemodynamically unstable.

Inappropriate Detection of a Supraventricular Tachycardia as Dual Tachycardia by the PR Logic™ Algorithm

Tachycardia detection and therapy algorithms in Implantable Cardioverter-Defibrillators (ICD) reduce, but do not eliminate inappropriate ICD shocks. Awareness of the pros and cons of a particular algorithm helps to predict its utility in specific situations. We report a case where PR logic™, an algorithm commonly used in currently implanted ICDs to differentiate supraventricular tachycardia (SVT) from ventricular tachycardia resulted in inappropriate detection and shock for an SVT, and discuss several solutions to the problem.

Dynamic analysis of cardiac rhythms for discriminating atrial fibrillation from lethal ventricular arrhythmias

BACKGROUND

Implantable cardioverter-defibrillators (ICDs), the first line of therapy for preventing sudden cardiac death in high-risk patients, deliver appropriate shocks for termination of ventricular tachycardia (VT)/ventricular fibrillation. A common shortcoming of ICDs is imperfect rhythm discrimination, resulting in the delivery of inappropriate shocks for atrial fibrillation (AF). An underexplored area for rhythm discrimination is the difference in dynamic properties between AF and VT/ventricular fibrillation. We hypothesized that the higher entropy of rapid cardiac rhythms preceding ICD shocks distinguishes AF from VT/ventricular fibrillation.

METHODS AND RESULTS

In a multicenter, prospective, observational study of patients with primary prevention ICDs, 119 patients received shocks from ICDs with stored, retrievable intracardiac electrograms. Blinded adjudication revealed shocks were delivered for VT/ventricular fibrillation (62%), AF (23%), and supraventricular tachycardia (15%). Entropy estimation of only 9 ventricular intervals before ICD shocks accurately distinguished AF (receiver operating characteristic curve area, 0.98; 95% confidence intervals, 0.93-1.0) and outperformed contemporary ICD rhythm discrimination algorithms.

CONCLUSIONS

This new strategy for AF discrimination based on entropy estimation expands on simpler concepts of variability, performs well at fast heart rates, and has potential for broad clinical application.

Improvement of left ventricular function under cardiac resynchronization therapy goes along with a reduced incidence of ventricular arrhythmia

Objectives

The beneficial effects of cardiac resynchronization therapy (CRT) are thought to result from favorable left ventricular (LV) reverse remodeling, however CRT is only successful in about 70% of patients. Whether response to CRT is associated with a decrease in ventricular arrhythmias (VA) is still discussed controversially. Therefore, we investigated the incidence of VA in CRT responders in comparison with non-responders.

Methods

In this nonrandomized, two-center, observational study patients with moderate-to-severe heart failure, LV ejection fraction (LVEF) ≤35%, and QRS duration >120 ms undergoing CRT were included. After 6 months patients were classified as CRT responders or non-responders. Incidence of VA was compared between both groups by Kaplan-Meier analysis and Cox regression analysis. ROC analysis was performed to determine the aptitude of LVEF cut-off values to predict VA.

Results

In total 126 consecutive patients (64±11years; 67%male) were included, 74 were classified as responders and 52 as non-responders. While the mean LVEF at baseline was comparable in both groups (25±7% vs. 24±8%; P = 0.4583) only the responder group showed an improvement of LVEF (36±6% vs. 24±7; p<0.0001) under CRT. In total in 56 patients VA were observed during a mean follow-up of 28±14 months, with CRT responders experiencing fewer VA than non-responders (35% vs. 58%, p<0.0061). Secondary preventive CRT implantation was associated with a higher likelihood of VA. As determined by ROC analysis an increase of LVEF by >7% was found to be a predictor of a significantly lower incidence of VA (AUC = 0.606).

Conclusions

Improvement of left ventricular function under cardiac resynchronization therapy goes along with a reduced incidence of ventricular arrhythmia.

Ventricular arrhythmias and sudden cardiac death

Management strategies for ventricular arrhythmias are guided by the risk of sudden death and severity of symptoms. Patients with a substantial risk of sudden death usually need an implantable cardioverter defibrillator (ICD). Although ICDs effectively end most episodes of ventricular tachycardia or ventricular fibrillation and decrease mortality in specific populations of patients, they have inherent risks and limitations. Generally, antiarrhythmic drugs do not provide sufficient protection from sudden death, but do have a role in reducing arrhythmias that cause symptoms. Catheter ablation is likewise important for reducing the frequency of spontaneous arrhythmias and is curative for some patients, usually those with idiopathic arrhythmias and no heart disease. Arrhythmia surgery is now infrequent, offered by only a few specialised centres for refractory arrhythmias. Advances in understanding of genetic arrhythmia syndromes and in technology for mapping and ablation of ventricular arrhythmias, and enhanced algorithms in implantable devices for rhythm management, have contributed to improved outcomes.