Diagnostic Electrophysiology Study Research Articles

Cardiac Arrhythmias and Their Management: An In-Depth Review of Current Practices and Emerging Therapies.

Cardiac arrhythmias encompass a range of conditions characterized by abnormal heart rhythms, affecting millions globally and significantly contributing to morbidity and mortality. This review provides a comprehensive analysis of the current practices and emerging therapies in managing cardiac arrhythmias, covering their definition, classification, epidemiology, and the critical importance of effective management. It explores the pathophysiology underlying various arrhythmias, including the mechanisms of arrhythmogenesis, such as re-entry, automaticity, and triggered activity. The review details the latest diagnostic tools, including ECG, Holter monitoring, and electrophysiological studies, and discusses the clinical presentation of different arrhythmias, from supraventricular to ventricular types and bradyarrhythmias. We examine current pharmacological and non-pharmacological treatment strategies, such as antiarrhythmic drugs, catheter ablation, and device therapy, highlighting their efficacy and limitations. Furthermore, the review delves into emerging therapies, including advanced catheter ablation techniques, novel antiarrhythmic agents, gene therapy, and innovative device technologies like leadless pacemakers and subcutaneous implantable cardioverter-defibrillators (ICDs). Special considerations for managing arrhythmias in diverse populations, including pediatrics, the elderly, and pregnant women, are discussed. Additionally, the review explores future directions in arrhythmia management, emphasizing personalized medicine, artificial intelligence applications, and the integration of advanced technologies in diagnosis and treatment. By synthesizing current knowledge and prospects, this review aims to enhance understanding and promote advancements in the field, ultimately improving patient outcomes with cardiac arrhythmias.

Is electrophysiological study a novel predictor for permanent pacemaker implantation after transcatheter aortic valve implantation?

Despite advancements in valve technology and increased clinical experience, complications related to conduction defects after transcatheter aortic valve implantation (TAVR) have not improved as rapidly as expected. In this study, we aimed to predict the development of complete atrioventricular (AV) block and bundle branch block during and after the TAVR procedure and to investigate any changes in the cardiac conduction system before and after the procedure using electrophysiological study. A total of 30 patients who were scheduled for TAVR at our cardiovascular council were planned to be included in the study. TAVR was performed on patients at Erciyes University Medical Faculty Hospital as a single center between May 2019 and August 2020 Diagnostic electrophysiological study was performed before the TAVR procedure and after its completion. Changes in the cardiac conduction system during the preprocedure, intra-procedure, and postprocedure periods were recorded. Significant increases in baseline cycle length, atrial-His (AH) interval, his-ventricular (HV) interval and atrioventricular (AV) distance were observed before and after the TAVR procedure (p = 0.039, p < 0.001, p = 0.018, p < 0.001, respectively). During the TAVR procedure, the preprocedural HV interval was longer in patients who developed AV block and bundle branch block compared to those who did not and this difference was statistically significant (p = 0.024). ROC curve analysis revealed that a TAVR preprocedure HV value >59.5 ms had 86% specificity and 75% sensitivity in detecting AV block and bundle branch block (AUC = 0.83, 95% CI: 0.664-0.996, p = 0.013). The preprocedure HV distance was 98 ± 10.55ms in the group with permanent pacemaker implantation and the mean value in the group without permanent pacemaker implantation was 66.27 ± 15.55 ms, showing a borderline significant difference (p = 0.049). The prolongation of HV interval in patients with AV block and bundle branch block suggests that the block predominantly occurs at the infra-hisian level. Patients with longer preprocedural HV intervals should be closely monitored for the need for permanent pacemaker implantation after the TAVR procedure.

Diagnostic Electrophysiology Study: The Auckland Regional Experience

Auckland City Hospital provides electrophysiology (EP) procedures for people residing in the Northern Region and is a national service for paediatric and congenital cardiac patients. Electrophysiology procedures are primarily therapeutic and typically undertaken with a view to ablation. When ablation is not delivered, these procedures are considered diagnostic. This retrospective study was undertaken to explore the clinical characteristics and outcomes of patients who underwent diagnostic EP study. The Auckland City Hospital Electrophysiology Registry was reviewed and patients who underwent an EP procedure without ablation from 1 June 2020 to 31 December 2021 were included. Patient characteristics, indications, procedure prioritisation, study indication, reason for no ablation, antiarrhythmic medications, procedure outcomes, and complications were reviewed. There were 912 procedures, 79 (8.7%) were diagnostic EP studies alone. Patients were aged 3–83 years (median, 41). Ethnicities included NZ European (54%) and Māori (18%). The indication in 56 patients was for an assessment of palpations. The most common reason for no ablation undertaken was no inducible tachycardia (n=36). Other reasons included no accessory pathway identified, high-risk procedure due to proximity to the AV node, and no ablation was intended (i.e., for VT stimulation). There were three reported complications: one moderate pericardial effusion that did not require intervention, one VT/VF arrest, and one access site haematoma. Diagnostic EP studies remain common with acceptable complication rates.

Invasive electrophysiology study guided loop recorder implantation in myotonic dystrophy type 1: a prospective single-center study

Abstract Funding Acknowledgements Type of funding sources: None. Introduction In one third of the patients with myotonic dystrophy type 1 (DMT1) the cause of death is of cardiac origin. The most common cardiac manifestations are arrhythmias and conduction disturbances. Purpose Due to its extreme long monitoring properties, implantable loop recorders (ILRs) are highly suitable to detect rare cardiac arrhythmias. To date, there are only limited data using ILRs in DMT1. We aimed to evaluate the role of the invasive electrophysiology study (EPS)-guided loop recorder implantation in patients with DMT. Methods In our prospective study 18 genetically confirmed DMT1 patients underwent non-invasive cardiac examination including transthoracic echocardiography, 24-hour Holter monitoring and surface ECG. In addition, EPS was performed in all cases to evaluate the risk of sudden cardiac death and infra-Hisian conduction properties. Based on the performed non-invasive diagnostic evaluation and EPS findings, patients were divided into low, intermediate and high-risk groups. For patients with normal investigation results and normal HV interval (&amp;lt;55 ms) only annual cardiac follow-up visits were planned (low-risk group). Patients with increased PR interval (&amp;gt;240 ms), QRS duration (&amp;gt;120 ms), or slightly prolonged HV interval (55-70 ms) underwent implantable loop recorder (ILR) implantation (intermediate-risk group). Permanent pacemaker (PM) or implantable cardiac defibrillator (ICD) was implanted in patients with 2nd/3rd degree atrioventricular block (AVB), significantly prolonged HV interval (&amp;gt;100 ms) or if sustained ventricular tachyarrhythmia could be induced during EPS. All patients were followed for at least 3 years. Results According to our study criteria, 8 patients could be categorized as "intermediate risk", 7 of them received implantable loop recorder (ILR). 1 ILR had to be removed 3 weeks after implantation due to skin infarction. During three-years of follow-up, 2 patients had many asymptomatic atrial high-rate episodes, but no 2nd or 3rd degree AVB, significant asystole or malignant ventricular arrhythmia were detected. Conclusions Our single-center prospective study examined the EPS-guided ILR implantation for the risk stratification of DMT1 patients for the first time. A more extensive, multicenter study is warranted to define optimal management of DMT1 patients with slightly impaired infrahisian conduction.

PO-03-147 EVALUATION OF A PEDIATRIC ELECTROPHYSIOLOGY CASE COMPLEXITY PREDICTION MODEL TO OPTIMIZE PROCEDURAL SCHEDULING

While operational efficiency has been evaluated in adult interventional and surgical specialties, limited data exist regarding the prediction of case complexity in the pediatric and congenital electrophysiology (EP) laboratory. To identify pre-procedural variables that predict prolonged case durations among pediatric and adult congenital patients presenting for diagnostic EP study and catheter ablation. A retrospective cross-sectional study was performed of all EP studies performed at Boston Children’s Hospital between 1/1/2015-1/1/2020 including pediatric and adult congenital heart disease patients of all ages. The primary outcome was case duration ≥180 minutes. Univariate and multivariate analyses were performed for the primary outcome using logistic regression, with a sub-analysis repeated for pediatric patients <20 years of age. During the 5-year period, 1025 patients underwent EP study and 292 (28.5%) had a case duration ≥180 minutes. Factors associated with the primary outcome on multivariate analysis were: age ≥20 years at EP study (OR 1.95, 95% CI 1.24-3.07, p 0.004), arrhythmia diagnosis of premature ventricular contractions/ventricular tachycardia (PVC/VT, OR 3.70, 95% CI 2.10-6.55, p <0.001), Fontan (OR 3.74, 95% CI 1.69-8.30, p=0.001) or Mustard/Senning physiology (OR 4.13, 95% CI 1.48-11.60, p=0.007), and the presence of non-cardiac comorbidities (OR 2.47, 95% CI 1.29-4.73, p 0.006). Restricting the analysis to pediatric patients <20 years old, factors associated with the primary outcome on multivariate analysis were an arrhythmia diagnosis of PVC/VT (OR 3.04, 95% CI 1.64-5.63, p <0.001), Fontan physiology (OR 3.13, 95% CI 1.10-8.92, p 0.033), non-cardiac comorbidities (OR 4.32, 95% CI 2.07-9.01, p <0.001), and prior ablation (OR 1.58, 95% CI 1.03-2.41, p 0.035). Intra-atrial reentrant tachycardia was not associated with prolonged case duration in either multivariate model. A weighted risk score using factors identified on multivariate analyses correctly classified procedures with prolonged case duration with reasonable accuracy (c-statistic 0.70). Age-dependent anatomic, electrophysiologic, and comorbid factors are associated with prolonged case duration in the pediatric and congenital EP laboratory. Applying a simple risk score using pre-procedural variables can discriminate cases with and without prolonged duration, and may aid in efficient procedural scheduling practices.

Proposing national diagnostic reference levels for electrophysiology studies and catheter ablation procedures in Bulgaria

IntroductionThe implementation of diagnostic reference levels (DRLs) is an essential tool for optimisation of the routine practice, better management of patient exposure while maintaining sufficient image quality. National DRLs for electrophysiology (EP) procedures are not available in our country. PurposeThe main purpose of the study was to propose, for first time in Bulgaria, national DRLs (NDRLs) for EP studies and ablation procedures of two different levels of complexity. The proposed DRLs can be later used to establish NDRLs by the national authority with regulatory functions related to medical exposure. MethodA retrospective study was done with the three highest volume Bulgarian EP centers, where over 95% of all cardiac ablations were performed. Data were extracted from the electronic registry for invasive electrophysiology BG-EPHY. Independently of the proposed NDRLs, we also compared the air kerma-area product (KAP) between the participating centers for procedures of the same level of complexity. ResultsThe proposed NDRL in terms of KAP were: 5.2 Gy.cm2 for diagnostic EP studies, 25.5 Gy.cm2 for simple ablations, and 52.1 Gy.cm2 for complex ablations. There was a significant variation in KAP for procedures with the same degree of complexity within each center. ConclusionThis study is the first to propose NDLRs for EP studies and ablation procedures of two levels of complexity in Bulgaria. The results identified EP procedures requiring further optimization of patient protection and provided a basis for future comparisons and standardization with further investigations on the topic. The proposed NDRLs are recommended to be used for better management of radiation exposure during EP procedures of different levels of complexity.

Para-Hisian pacing in a patient with a long RP tachycardia-What is the mechanism?

A 29-year-old man underwent a diagnostic electrophysiology study because of a recurrent symptomatic long RP supraventricular tachycardia (SVT). Twelve-lead electrocardiography and echocardiography were normal. Atrio-His (AH) and His-ventricular intervals measured 86 and 52 ms, respectively. The patient had retrograde ventriculoatrial (VA) activation that was midline and decremental. Para-Hisian pacing repeatedly induced his clinical SVT (Figure 1, top). The response to His-refractory ventricular premature depolarizations and entrainment from the ventricle are shown (Figure 1, middle and bottom).

Delayed termination and transformation of a supraventricular tachycardia—What is the mechanism?

A 75-year-old woman underwent a diagnostic electrophysiology study because of a recurrent, symptomatic, drug-refractory supraventricular tachycardia (SVT). The 12-lead electrocardiogram showed only mild PR prolongation. Atrio-His and His-ventricular intervals measured 140 and 45 ms, respectively. She demonstrated retrograde ventriculoatrial activation that was earliest at the anteroseptum and decremental. Single atrial extrastimulation and spontaneous atrial premature depolarizations (APDs) repeatedly induced a short RP SVT.

Nine reasons for performing an electrophysiology study in patients with apparently idiopathic ventricular fibrillation.

Idiopathic ventricular fibrillation (IVF) occurs in approximately 10% of patients resuscitated from cardiac arrest.1 When magnetic resonance imaging, exercise stress or epinephrine testing, and sodium channel blocker challenge are normal, there is a strong suspicion of IVF diagnosis,2 and many cardiac electrophysiologists are proceeding with implantable cardioverter-defibrillator (ICD) implantation without performing a diagnostic electrophysiology study (EPS) (“knee-jerk” ICD implantation).

An unusual incessant long RP tachycardia—What is the mechanism?

A 40-year-old man underwent a diagnostic electrophysiology study because of a slow incessant long RP supraventricular tachycardia (SVT). Echocardiography revealed an ejection fraction of 35%. Upon presentation to the electrophysiology laboratory, he was in SVT. His refractory ventricular premature depolarizations (VPDs) delivered from the right ventricular (RV) apex failed to affect the tachycardia; the responses to earlier VPDs and coronary sinus (CS) atrial premature depolarizations (APDs) are shown in Figure 1, top and bottom, respectively.

High-sensitivity cardiac troponin and C-reactive protein dynamics after cardiac electrophysiological procedures

The catheter ablation of cardiac arrhythmias causes myocardial destruction and increase of the cardiac troponin and C-reactive protein (CRP). Data regarding dynamics of high-sensitivity troponin during irrigated ablation are scarce, and for diagnostic electrophysiological studies (EPS) are lacking. We aimed to study the periprocedural dynamics of high-sensitivity cardiac troponin I (hscTn I) and CRP, as well as their relation to different procedural parameters during EPS and ablation of various arrhythmias. Material and methods: Consecutive patients with EPS or ablation performed were studied prospectively. Clinical and procedural characteristics, and pre- and postprocedural values of hscTn I and CRP are presented at days 1, 2 and 3. Six indices were chosen as procedural markers of induced myocardial injury. P-value &amp;#60; 0.05 was accepted as statistically signifi cant for all tests performed. Results: Eight EPS and 98 ablations were performed in 103 patients (58 males, 56.3%). For ablations the baseline values of hscTn I at day 1 were 3.2 ng/L (1.7-4.93), while postprocedural values at days 2 and 3 were 500 ng/L (269-1044) and 404 ng/L (179-1017), р &amp;#60; 0.05 for all days. Postprocedural hscTn I values were moderately to strongly correlated to radiofrequency (RF) energy, time and number of RF applications. Postprocedural increase of CRP was also significant, but its magnitude was much smaller. Its correlation to procedural indices was weak. For EPS the baseline values of hscTn I were 5.95 ± 5.34 ng/L (0.6-15.9), while for the next 2 days these were 53.2 ± 43.1 ng/L (13.3-144) и 16.7 ± 9.65 ng/L (3.3-30.9), р &amp;#60; 0.05 for all days. Conclusion: Signifi cant postprocedural increase of hscTn I was detected in all electrophysiology procedures – EPS and ablations. This increase was more pronounced and prolonged to at least the next day after ablation. It was clearly correlated to the cumulative RF energy, RF time and number of RF applications. Early increase of CRP was also signifi cant, but to a lesser magnitude and in weak correlation to the procedural parameters.

Differences in ventricular tachycardia inducibility in patients with Tetralogy of Fallot depending on the clinical indication for the electrophysiologic study

Abstract Introduction The arrhythmic risk stratification of patients with repaired Tetralogy of Fallot (TOF) is still controversial. The performance of an electrophysiologic (EP) study before pulmonary valve replacement (PVR), regardless of patient's risk factors, is an extended practice in some centers that is not recommended in current guidelines. The aim of our study was to explore the differences in ventricular tachycardia (VT) inducibility in patients with TOF during programmed ventricular stimulation (PVS) depending on the clinical indication. Methods All patients with repaired TOF who underwent an EP study with PVS between January 2001 and October 2020 were included. EP studies performed in the context of ventricular or supraventricular tachycardia ablations that had been previously diagnosed were excluded. We defined two clinical scenarios for performing the EP study: pre-PVR (performed previous to pulmonary valve replacement) or diagnostic EP study (performed due to high risk symptoms which included palpitations, syncope or presyncope). Baseline clinical information, electrocardiogram, echocardiogram and cardiac MRI parameters were retrospective recorded. Results A total of 139 EP studies with PVS were included; 87 in the pre-PVR group and 52 in the diagnostic EP study group. There was a greater incidence of palpitations, syncope and presyncope in the “Diagnostic EP study” group. Moreover, there were statistical significant differences in right ventricle dimensions and function between groups. The repair surgical approach was similar in both groups. It was detected a statistical significant difference in VT induction between the pre-PVR group and the diagnostic indicated group (16,1% vs 34,6%, p=0,012). Conclusions Differences in VT induction are observed during PVS performing in TOF patients depending on the clinical indication. Symptomatology is an important parameter that must be taken into account in order to decide whether to perform an EP study in this population. Funding Acknowledgement Type of funding sources: None.

Case Report

A patient suffered from recurrent episodes of palpitations and documented wide QRS complex tachycardia. Echocardiography revealed no obvious abnormal heart structure. A diagnostic electrophysiological study was performed and fast-slow atrioventricular nodal reentrant tachycardia with aberrancy was diagnosed. Successful slow pathway ablation rendered the tachycardia noninducible.

The survey of electrophysiology lab activity during the COVID-19 pandemic.

BackgroundWith the onset and spread of the COVID‐19 pandemic, the hospitalization and treatment of noncovid patients were dramatically affected. The aim of this study is to evaluate the electrophysiology (EP) lab activity in a referral center in Iran during the COVID‐19 era.MethodsA cross‐sectional descriptive survey was conducted on EP lab activity in Shahid Chamran Heart Center, Isfahan, Iran. Two periods of COVID‐19 occurrence peaks in Iran were compared with same date in 2019. Information was collected on number of diagnostic and therapeutic electrophysiology studies (EPSs) and implantation of intracardiac devices such as permanent pacemaker (PPM), implantable cardioverter defibrillator (ICD), and cardiac resynchronization therapy (CRT).ResultsIn the first peak of COVID‐19 pandemic, both of EPSs and intracardiac device implantations decreased by 80% compared to the same period in 2019. The most common type of device implanted during this period was PPM (70%); however, at the time of control, the ICD (73%) was the most common. Paroxysmal supraventricular tachyarrhythmia (PSVT) was the best indication for diagnostic and therapeutic EPSs in covid and control periods. In the second peak of prevalence of COVID‐19 virus infection in Iran, 6% and 36% decreases in device implantations and EPSs were seen, respectively. During this period, the number of procedures increased, although it was still lower than in 2019.ConclusionA significant reduction in the EP lab activity has been observed during both the COVID‐19 pandemic peaks.

Hidden under the Surface: A Rare Cause of Repeated Syncope in a Patient with Recent Pacemaker Implantation

A 66-year-old woman received a pacemaker implantation because of syncope with documented sinus arrest and junctional bradycardia. Three weeks later the pacemaker analysis revealed episodes of nonsustained ventricular tachycardia. Coronary angiography and invasive coronary assessment showed diffuse moderate stenosis but no significant ischemia. Three months later she experienced a new syncope and the pacemaker analysis showed runs of nonsustained ventricular tachycardia at the time of syncope. The combination of brady- and tachyarrhythmias raised concern for cardiac sarcoidosis. 18F-fluorodeoxyglucose positron emission tomography (PET) scan showed increased FDG uptake in the basal segments compatible with inflammatory disease. Cardiac magnetic resonance imaging showed late gadolinium enhancement in the same region of the PET-avid lesions. Diagnostic electrophysiologic study could induce VT. The diagnosis of cardiac sarcoidosis was made, for which high dose corticosteroids were prescribed and an upgrade to a dual chamber implantable cardioverter defibrillator was performed. Because of the localization of the lesions, an endomyocardial biopsy was not performed. All the lesions regressed completely on PET-scan after treatment with high dose corticosteroids.

Change of Paradigm in the Management of Patients with Accessory Pathways over the Last Forty Years: Wolff-Parkinson-White Syndrome as an Electrophysiological Marvel at Risk of Extinction.

Over the last decades, the approach to the Wolff-Parkinson-White syndrome, as well as its treatment, has substantially changed, leading to improvement in the prognosis and quality of life of these patients. From the first diagnostic electrophysiologic studies to the most recent evaluations, important data on pathophysiologic and clinical aspects have been gathered, and this learning journey is still not concluded. This body of knowledge is a fundamental part of any cardiologists' armamentarium despite the fact that this syndrome is rarely observed in adult patients.

Fluoroscopy time and scattered radiation during electrophysiology procedures: analysis of one-year data of a laboratory providing electrophysiology training

Objectives Patients and medical staff expose to significant radiation during electro-physiological (EP) procedures. There are few data regarding the leading factors of longer fluoroscopy time and higher scattered radiation in a laboratory giving EP training during those interventions. Material and methods The patients’ recordings that underwent EP procedure in a single centre arrhythmia unit from February 2019 to January 2020 were examined. Prospectively collected data regarding procedure duration, fluoroscopy time and total air kerma, demographic characteristics of the patients, type of procedure, success of ablation and the use of electro anatomic mapping were retrospectively evaluated. Predictors of total air kerma were analysed with linear regression analysis. Results Study population consisted of 437 patients with a median age of 47 (39–56); 184 (42.1%) were male. Median fluoroscopy time was 768 (420–1320) seconds and median cumulative air kerma was 369 (191–750) mGy. Fluoroscopy time and cumulative air kerma were significantly lower in diagnostic EP studies compared to other procedures. There was no difference in terms of total air kerma between the procedures other than the diagnostic EP study. In multivariable linear regression analysis; body surface area, fluoroscopy time, not using the electro-anatomical mapping, unsuccessful ablation and atrial flutter ablation were predictors of total air kerma in EP studies performed by trainees. Conclusion Scattered radiation during EP procedures performed by in-training operators is related with some factors. Awareness about those may help to effort reducing the harmful effect of ionising radiation.

Incessant palpitations in a young male.

27-year-old male with incessant palpitations and reduced ejection fraction presents for diagnostic electrophysiology study. ECG shows a long RP tachycardia. Permanent junctional reciprocating tachycardia is diagnosed on EP study with successful ablation of posteroseptal accessory pathway.

Outcome of cardiac tamponades in interventional electrophysiology.

The aim of this study was to analyse tamponades following electrophysiological procedures regarding frequency and mortality in a high-volume centre and to identify independent predictors for severe tamponades. We performed a retrospective study on 34982 consecutive patients undergoing diagnostic electrophysiological studies or catheter ablation of cardiac arrhythmias. The combined endpoint was defined as severe tamponade. Criteria for severe tamponade included surgical repair, repeat pericardiocentesis, cardiopulmonary resuscitation, intrahospital death or death during follow-up, and thrombo-embolic events or complications due to therapeutic management. Multivariate analysis was performed to identify independent predictors for severe tamponade. A total of 226 tamponades were identified. Overall frequency of tamponades was 0.6%. Procedures requiring epicardial approach had the highest rate of tamponades (9.4%). Twenty-nine patients with tamponade underwent surgery (12.8% of all tamponades and 21.4% of tamponades during epicardial procedures). Overall tamponade-related mortality was 0.03% (9 deaths). Fifty-six patients (24.8%) experienced severe tamponade. Independent risk factors for severe tamponades were endocardial ablation of ventricular tachycardia, epicardial approach, balloon device ablation, high aspiration volume during pericardiocentesis and structural heart disease. The frequency of tamponades is strongly dependent on the type of procedure performed. Overall tamponade-related mortality was low but significantly higher in patients undergoing epicardial procedures. Surgical backup should be considered for patients undergoing complex ventricular tachycardia ablation and left atrial ablation procedures.

Implantable Cardioverter-Defibrillators and Wearable Defibrillators: Guidelines and Updates.

Implantable cardioverter-defibrillators (ICDs) have been a preferred treatment for ventricular arrhythmias. Clinical data have consistently supported their use; however, determining which patients will or will not benefit from treatment remains difficult.A documented episode of sustained ventricular tachycardia/ventricular fibrillation (VT/VF) without reversible cause warrants ICD implantation (class IA indication) to potentially treat episodes in the future.1 In patients without prior VT/VF, decreased left ventricular ejection fraction (LVEF) is the primary indication for preemptive ICD implantation. If the LVEF is ≤0.35 despite maximal guideline-directed medical therapy, or coronary revascularization was performed 90 or more days previously, then ICD implantation is a class I indication,1 in ischemic or nonischemic cardiomyopathy. An LVEF ≤0.35 in a patient with myocardial infarction (MI) who has been on medical therapy for 40 days also meets the guidelines for ICD implantation.1In addition to LVEF, other factors indicate which patients may benefit from ICD therapy. Diagnostic electrophysiologic studies (EPS), for example, have been part of risk-stratifying patients for more than 20 years. The Multicenter Unsustained Tachycardia Trial (Mustt) investigators categorized post-MI patients with nonsustained VT and an LVEF ≤0.40 according to whether ventricular arrhythmias were induced during EPS; the patients with inducible VT during EPS benefited from ICD implantation.2 Inducible VT/VF during EPS is also an indication for ICD implantation in patients with coronary artery disease who are at risk for ventricular arrhythmias, which present as unexplained syncope, immediately after MI.1Cardiac imaging is another diagnostic method that is playing a more prominent role in stratifying the risks of sudden death. In particular, cardiac magnetic resonance (CMR) has shown promise in evaluating intrinsic myocardial scarring and predicting cardiac death in patients with hypertrophic cardiomyopathy.3 However, its usefulness in determining the need for ICD therapy has not been fully established. An ongoing clinical trial, Cardioverter-Defibrillator Implantation to Prevent Tachyarrhythmias following Acute Myocardial Infarction (Protect-ICD) (NCT 03588286), is evaluating the use of both EPS and CMR to identify which post-MI patients could benefit from ICD treatment.It is unclear how best to monitor and prevent ventricular arrhythmias in patients with a decreased LVEF who are still undergoing optimal medical therapy within 90 days after MI. While being considered for ICD treatment, these patients may benefit from treatment with a wearable cardioverter-defibrillator. This vest-like device, which is worn under clothing, continuously monitors heart rhythm and delivers a shock to restore sinus rhythm in patients who have sustained VT/VF. Currently, using a wearable defibrillator is a class IIB indication in patients who are at high risk for sudden death but do not meet other immediate indications for ICD therapy.1 The Vest Prevention of Early Sudden Death Trial (VEST) investigators randomized post-MI patients with LVEF ≤0.35 in a 2:1 ratio to receive a wearable defibrillator and medical therapy (device group) or medical therapy alone (control group). There were no differences between groups in the primary outcome of arrhythmic death (device group, 1.6%; control group, 2.4%; P=0.18), whereas the overall mortality rate was lower in the device group (3.1% vs 4.9%; P=0.04).4An inherent limitation of the wearable defibrillator is compliance. For example, VEST trial participants wore it for only 14 hr/d, on average.4 In addition, the relatively low event rate suggests that the trial was underpowered to evaluate differences within the groups. Although no clear benefit was found with regard to arrhythmic death, the lower mortality rate in the defibrillator group suggested benefit from monitoring rhythm.In summary, ICD treatment remains important in managing ventricular arrhythmias. Current guidelines support ICD implantation in patients with prior episodes of VT/VF, and LVEF ≤0.35, or both. Further studies should clarify the value of wearable defibrillators and confirm the roles of EPS and CMR in determining which patients will benefit most from ICD implantation.