Left Ventricular Summit-Concept, Anatomical Structure and Clinical Significance

Prevalence and electrocardiographic and electrophysiological characteristics of idiopathic ventricular arrhythmias originating from the septal left ventricular summit

INTRODUCTION

The left ventricular summit (LVS) is the highest point on the epicardial surface of the left ventricle. A part of the LVS that is located between the left coronary arteries (lateral-LVS) is one of the major sites of idiopathic ventricular arrhythmia (VA) origins. Some idiopathic epicardial VAs can be ablated at endocardial sites adjacent to the epicardial area septal to the lateral-LVS (septal-LVS). This study examined the prevalence and electrocardiographic and electrophysiological characteristics of septal-LVS VAs.

METHODS

We studied consecutive patients with idiopathic VAs originating from the LVS (67 patients) and aortic root (93 patients).

RESULTS

Based on the ablation results, among 67 LVS VAs, 54 were classified as lateral and 13 as septal-LVS VAs. As compared with the lateral-LVS VAs, the septal-LVS VAs were characterized by a greater prevalence of left bundle branch block with left inferior-axis QRS pattern, later precordial transition, lower R-wave amplitude ratio in leads III to II, lower Q-wave amplitude ratio in leads aVL to aVR, and later local ventricular activation time relative to the QRS onset during VAs (V-QRS) in the great cardiac vein. The electrocardiographic and electrophysiological characteristics of the septal-LVS VAs were similar to those of the aortic root VAs. However, the V-QRS at the successful ablation site was significantly later during the septal-LVS VAs than aortic root VAs (p < .0001). The precordial transition was significantly later during the septal-LVS VAs than aortic root VAs (p < .05).

CONCLUSIONS

Septal-LVS VAs are considered a distinct subgroup of idiopathic VAs originating from the left ventricular outflow tract.

Definition and anatomical description of the left atrial appendage neck

The left atrial appendage (LAA) is well known as a source of cardiac thrombus formation. Despite its clinical importance, the LAA neck is still anatomically poorly defined. Therefore, this study aimed to define the LAA neck and determine its morphometric characteristics. We performed three-dimensional reconstructions of the heart chambers based on contrast-enhanced electrocardiography-gated computed tomography scans of 200 patients (47% females, 66.5 ± 13.6 years old). The LAA neck was defined as a truncated cone-shaped canal bounded proximally by the LAA orifice and distally by the lobe origin and was present in 98.0% of cases. The central axis of the LAA neck was 14.7 ± 2.3 mm. The mean area of the LAA neck walls was 856.6 ± 316.7 mm2 . The LAA neck can be divided into aortic, arterial (the smallest), venous (the largest), and free surfaces. All areas have a trapezoidal shape with a broader proximal base. There were no statistically significant differences in the morphometric characteristics of the LAA neck between LAA types. Statistically significant differences between the sexes in the main morphometric parameters of the LAA neck were found in the central axis length and the LAA neck wall area. The LAA neck can be evaluated from computed tomography scans and their three-dimensional reconstructions. The current study provides a complex morphometric analysis of the LAA neck. The precise definition and morphometric details of the LAA neck presented in this study may influence the effectiveness and safety of LAA exclusion procedures.

Mapping and ablation of ventricular arrhythmias arising from the left ventricular summit

The left ventricular summit (LVS) refers to the highest portion of the left ventricular outflow tract (LVOT). It is an epicardially delimited triangular area by the left coronary arteries and the coronary venous circulation. Its deep myocardium correlates closely with the left coronary cusp, aortic-mitral continuity, and right ventricular outflow tract (RVOT), complicating the anatomical relationship. Ventricular arrhythmias (VAs) originating from this area are common, accounting for 14.5% of all VAs origin from left ventricle. Specific electrocardiogram (ECG) characteristics may assist in locating LVS-VAs pre-procedure and facilitate procedure planning. However, catheter ablation of LVS-VAs remains challenging because of anatomical constraints. This paper reviews the recent understanding of LVS anatomy, concludes ECG characteristics, and summarizes current mapping and ablation methods for LVS-VAs.

Outcomes of Catheter Ablation of Left Ventricular Summit Arrhythmias

The left ventricular summit (LVS) is the area in the highest portion of the left ventricular epicardium, bounded by the left coronary arteries and the coronary venous circulation, and can be surrounded by thick epicardial fat that may preclude epicardial ablation. Ablation of LVS ventricular arrhythmias (VA) can be achieved from adjacent structures with good success rates. The long-term freedom from LVS VA recurrence remains variable. This article reviews the spatial and anatomic relationship of the structures surrounding the LVS, which provide vantage points for ablation, and the acute and long-term outcomes of different ablation approaches in LVS VA ablation.

Deductive Electrocardiographic Analysis of Left Ventricular Summit Arrhythmias

The left ventricular summit is a source of idiopathic ventricular arrhythmias and presents distinct challenges for mapping and ablation. These arrhythmias are typically targeted from the distal coronary venous system or most often from endocardial vantage points such as the left coronary cusp, basal left ventricle or septal right ventricular outflow tract. In this article, we review the electrocardiographic patterns that suggest a possible origin from the left ventricular summit and the features that may help to predict the most likely site of successful ablation.

Preventing Complications During Mapping and Ablation of Left Ventricular Summit Arrhythmias

The left ventricular summit is a site of origin for idiopathic ventricular arrhythmias. With advancements in mapping and ablation techniques, sites previously considered inaccessible can now be approached. Anatomical knowledge of the 3-dimensional landmarks of this space is important, as critical structures reside within its boundaries and are potentially liable to collateral injury during ablation. This article reviews reported complications from ablation of ventricular arrhythmias arising from the left ventricular summit and its vicinity and discusses the pros and cons of different ablation technique and the role of an individualized anatomical approach to reduce procedural related complications and improve outcomes.

Magnetic Resonance Assessment of Ejection Fraction Versus Echocardiography for Cardioverter-Defibrillator Implantation Eligibility

Simple Summary

Nonischemic cardiomyopathies with low left ventricular ejection fractions (LVEF) are eligible for an implantable cardioverter defibrillator. However, the guidelines do not specify which method should be used to assess LVEF. In our study we investigated the potential impact of performing two-dimensional echocardiography (2DE) compared to cardiovascular magnetic resonance (CMR) for LVEF regarding ICD eligibility. We found that 2DE both overestimated and especially underestimated the need for implantation, which can have serious implications in the quality of life and the prevention of death events.

Abstract

Background: The aim of this study was to investigate the potential impact of performing two-dimensional echocardiography (2DE) compared to cardiovascular magnetic resonance (CMR) for left ventricular ejection fraction (LVEF) on implantable cardioverter defibrillator (ICD) eligibility. Methods: A prospective cohort of 166 consecutive patients with nonischemic cardiomyopathy (NICM) was designed to compare transthoracic 2DE and CMR imaging. Results: Echocardiography measurements have important differences and large limits of agreement compared to CMR, especially when assessing ventricle volumes, and smaller but relevant differences when assessing LVEF. The agreement between CMR and 2DE regarding the identification of subjects with EF <= 35, respectively <= 30, and thus eligible for an ICD measured by Cohen’s Kappa was 0.78 (95% CI: 0.68–0.88), p < 0.001, respectively 0.65 (95% CI: 0.52–0.78), p < 0.001. The disagreement represented 7.9%/11.3% of the subjects who had EF < 35%/< 30% as observed by CMR, who would have been classified as eligible for an ICD, resulting in an additional need to use an ICD. Moreover, 2.6%/3.3% would have been deemed eligible by echocardiography for an ICD. Conclusions: These measurement problems result in incorrect assignments of eligibility that may have serious implications on the quality of life and the prevention of death events for patients assessed for eligibility of an ICD.