Publications

Heterogeneity in depolarization and repolarization among regions of cardiac cells has long been recognized as a major factor in cardiac arrhythmogenesis. This fundamental principle has motivated development of noninvasive techniques for quantification of heterogeneity using the surface electrocardiogram (ECG). The initial approaches focused on interval analysis such as interlead QT dispersion and Tpeak -Tend difference. However, because of inherent difficulties in measuring the termination point of the T wave and commonly encountered irregularities in the apex of the T wave, additional techniques have been pursued. The newer methods incorporate assessment of the entire morphology of the T wave and in some cases of the R wave as well. This goal has been accomplished using a number of promising vectorial approaches with the resting 12-lead ECG. An important limitation of vectorcardiographic analyses is that they require exquisite stability of the recordings and are not inherently suitable for use in exercise tolerance testing (ETT) and/or ambulatory ECG monitoring for provocative stress testing or evaluation of the influence of daily activities on cardiac electrical instability. The objectives of the present review are to describe a technique that has been under clinical evaluation for nearly a decade, termed "interlead ECG heterogeneity." Preclinical testing data will be briefly reviewed. We will discuss the main clinical findings with regard to sudden cardiac death risk stratification, heart failure evaluation, and myocardial ischemia detection using standard recording platforms including resting 12-lead ECG, ambulatory ECG monitoring, ETT, and pharmacologic stress testing in conjunction with single-photon emission computed tomography myocardial perfusion imaging.

Cardiac sarcoidosis (CS) is a complex disease that can manifest as a diverse array of arrhythmias. CS patients may be at higher risk for sudden cardiac death (SCD), and, in some cases, SCD may be the first presenting symptom of the underlying disease. As such, identification, risk stratification, and management of CS-related arrhythmia are crucial in the care of these patients. Left untreated, CS carries significant arrhythmogenic morbidity and mortality. Cardiac manifestations of CS are a consequence of an inflammatory process resulting in the myocardial deposition of noncaseating granulomas. Endomyocardial biopsy remains the gold standard for diagnosis; however, biopsy yield is limited by the patchy distribution of the granulomas. As such, recent guidelines have improved clinical diagnostic pathways relying on advanced cardiac imaging to help in the diagnosis of CS. To date, corticosteroids are the best studied agent to treat CS but are associated with significant risks and limited benefits. Implantable cardioverter-defibrillators have an important role in SCD risk reduction. Catheter ablation in conjunction with antiarrhythmics seems to reduce ventricular arrhythmia burden. However, the appropriate selection of these patients is crucial as ablation is likely more helpful in the setting of a myocardial scar substrate versus arrhythmia driven by active inflammation. Further studies investigating CS pathophysiology, the pathway to diagnosis, arrhythmogenic manifestations, and SCD risk stratification will be crucial to reduce the high morbidity and mortality of this disease.

Catheter-based ultrasonography is a widely used tool in cardiac electrophysiology practice, and intracardiac echocardiography is supplanting other forms of imaging to become the dominant imaging modality. Given advances in pericardial access, intrapericardial echocardiography can be performed using ultrasound catheters as well. Intrapericardial echocardiography and echocardiography from the coronary sinus, also an epicardial structure, allows interventionalists to obtain unique views from virtually any vantage point, compared with other forms of echocardiography. Both intrapericardial echocardiography and coronary sinus echocardiography are safe and important alternatives that can be used during complex procedures in the electrophysiology laboratory.

BACKGROUND: Drugs belonging to diverse therapeutic classes can prolong myocardial refractoriness or slow conduction. These drugs may be effective and well-tolerated, but the risk of sudden cardiac death from torsades de pointes (TdP) remains a major concern. The corrected QT interval has significant limitations when used for risk stratification. Measurement of global electrical heterogeneity (GEH) could help identify the substrate vulnerable to drug-induced ventricular arrhythmias.

OBJECTIVE: The purpose of this study was to improve risk stratification for drug-induced TdP by measuring GEH on the electrocardiogram (ECG).

METHODS: We analyzed ECG data from a case-control study of patients with a history of drug-induced TdP as well as age- and sex-matched controls. Vectorcardiograms were constructed from ECGs. GEH was measured via the spatial ventricular gradient (SVG) vector (magnitude, azimuth, and elevation). Log odds coefficients for TdP were estimated using multivariable logistic regression.

RESULTS: Among 17 cases (47% male; age 58.9 ± 12.5 years) and 17 controls (29% male; age 61.0 ± 12.2 years), 34 ECGs were analyzed. SVG azimuth was significantly different between cases and controls (3.4 vs 22.0 degrees, respectively; P = 0.02). After adjusting for sex and QTc interval, odds of TdP increased by a factor of 3.2 for each 1 SD change in SVG azimuth from the control group mean (95% confidence interval 1.07-9.14; P = .04). QTc was not significant in the multivariable analysis (P = .20).

CONCLUSION: SVG azimuth is correlated with a history of drug-induced TdP independent of QTc. GEH measurement may help identify patients at high risk for drug-induced arrhythmias.

Since their introduction >2 decades ago, percutaneous catheter-based epicardial mapping and ablation have become widely adopted by cardiac electrophysiologists around the world. Although epicardial mapping has been used for catheter ablation of a wide variety of cardiac arrhythmias, its most common use is for ablation of intramural and subepicardial substrates that give rise to ventricular tachycardia, particularly in patients with nonischemic cardiomyopathy. As such, the subxiphoid percutaneous epicardial approach has emerged as an important adjunct, and, in some cases, is the preferred strategy in this regard. This review discusses the rationale and indications for epicardial catheter mapping and/or ablation. This paper also reviews the prevalence of epicardial arrhythmias and their electrocardiographic criteria. In addition, it examines the anatomy of the pericardium and commonly used epicardial access techniques, as well as the optimal methodologies for epicardial mapping and ablation and the impact of epicardial fat. Finally, this review discusses the potential of the various complications associated with the percutaneous epicardial approach, in addition to patient-specific risk factors, and potential strategies to mitigate the risk of complications.

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Sudden cardiac death (SCD) is a major cause of mortality in elderly individuals owing to a high prevalence of coronary heart disease, systolic dysfunction, and congestive heart failure (CHF). Although the incidence of SCD increases with age, the proportion of cardiac deaths that are sudden decreases owing to high numbers of other cardiac causes of death in elderly individuals. Implantable cardioverter-defibrillator (ICD) therapy has been demonstrated to improve survival and prevent SCD in selected patients with systolic dysfunction and CHF. However, ICD therapy in elderly patients might not be effective because of a greater rate of pulseless electrical activity underlying SCD and other competing nonarrhythmic causes of death in this population. Although under-represented in randomized trials of ICD use, elderly patients comprise a substantial proportion of the population that qualifies for and receives an ICD for primary prevention under current guidelines. Cardiac resynchronization therapy (CRT), which has been demonstrated to reduce mortality in selected populations with heart failure, is also more commonly used in this group of patients than in younger individuals. In this Review, we examine the causes of SCD in elderly individuals, and discuss the existing evidence for effectiveness of ICD therapy and CRT in this growing population.