Left-axis deviation in patients with nonischemic heart failure and left bundle branch block is a purely electrical phenomenon

Current Role of Electrocardiographic Imaging in Patient Selection for Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) is a recognized therapy for heart failure with altered ejection fraction and abnormal left ventricular activation time. Since the introduction of the therapy, a 30% rate of non-responders is observed and unchanged. The 12-lead ECG remains the only recommended tool for patient selection to CRT. The 12-lead ECG is, however, limited in its inability to provide a precise pattern of regional electrical activity. Electrocardiographic imaging (ECGi) provides a non-invasive detailed mapping of cardiac activation and therefore appears as a promising tool for CRT candidates. The non-invasive ventricular activation maps acquired by ECGi have been primarily explored for the diagnosis and guidance of therapy in patients with atrial or ventricular tachyarrhythmia. However, the accuracy of the system in this field is lacking and needs further improvement before considering a clinical application. On the other hand, its use for patient selection for CRT is encouraging. In this review, we introduce the technical considerations and we describe how ECGi can precisely characterize ventricular activation, especially in patients with left bundle branch block, thus identifying the electrical substrate responsive to CRT.

The QRS frontal plane axis changes during left bundle branch block after transcatheter aortic valve replacement

BACKGROUND AND AIMS

Left bundle branch block (LBBB) is common after transcatheter aortic valve replacement (TAVR) and associated with a left or normal QRS axis. We aim to assess the QRS frontal plane axis shift changes during LBBB after TAVR and determine if the risk of procedure-related high degree atrioventricular block (AVB) is affected by QRS axis shift changes.

METHODS AND RESULTS

In a retrospective single-center study of 720 consecutive patients who underwent TAVR, 141 (19.6%) with normal baseline QRS duration developed a new LBBB after TAVR and constituted the study group. Most patients (59.6%) were females and the mean age of the cohort was 81.2 ± 6 years.

RESULTS

As compared with the baseline QRS axis before TAVR, the occurrence of LBBB was associated with a leftward QRS axis shift (by 40 ± 28.3°) in 73% of the study patients and a rightward (by 18.6 ± 19.4°) or no change in QRS axis in 25.6% and 1.4% of the study patients, respectively. A left QRS axis (-30°) was observed in 14.9% and 38.3% of the study patients before and after TAVR, respectively. The group of patients exhibiting a rightward or no QRS axis shift had a greater incidence of high degree AVB than the group of patients exhibiting a leftward QRS axis shift (18.4% vs. 6.8%, p = .056).

CONCLUSION

Although post TAVR-LBBB is associated with a leftward QRS axis shift in most patients, a non-negligible proportion of patients (27%) exhibited a rightward or no QRS axis shift. The latter group tend to have a higher risk of developing high degree AVB.

Relationship between left-axis deviation and onset of cardiac adverse events in right ventricular pacing

AIMS

The electrical axis shows alterations during right ventricular pacing (RVP), including a normal axis and left axis deviation; however, it remains unknown if differences in the electrical axis affect the occurrence of cardiac adverse events. The purpose of this study was to determine whether a left axis deviation increases the incidence of adverse cardiac events compared with a normal axis.

METHODS

This study analysed 156 patients with RVP. The patients were divided into two groups: those with left axis deviation after RVP (LAD group) and those with a normal axis (NA group). The primary composite outcome was the new-onset of atrial fibrillation (AF) and worsening heart failure (HF).

RESULTS

The QRS axis of the LAD (n = 77) and NA (n = 79) groups were - 64.5 ± 14.3° and 29.8 ± 36.5°, respectively (P < 0.001). The median follow-up was 1100 days and, regarding primary composite outcomes (hazard ratio, 1.03; 95% confidence interval, 0.64 to 1.65; P = 0.89), 29/77 (37.6%) and 28/79 (35.4%) patients in the LAD and NA groups, respectively, developed AF (hazard ratio, 1.07; 95% confidence interval, 0.64 to 1.81; P = 0.77). Furthermore, 8/77 (10.3%) and 12/79 (15.1%) patients in the LAD and NA groups, respectively, experienced worsening HF (hazard ratio, 0.65; 95% confidence interval, 0.26 to 1.60; P = 0.35).

CONCLUSION

The risk of cardiac adverse events in patients with RVP (new-onset AF or worsening HF, cardiovascular death, myocardial infarction, and stroke) and overall mortality with LAD is not higher than that with NA.

Preferred left ventricular lead position for upgrade from right ventricular pacing to cardiac resynchronization therapy

INTRODUCTION

Cardiac resynchronization therapy (CRT) is well-established for treating symptomatic heart failure with electrical dyssynchrony. The left ventricular (LV) lead position is recommended at LV posterolateral to lateral sites in patients with left bundle branch block; however, its preferred region remains unclear in patients being upgraded from right ventricular (RV) apical pacing to CRT. This study aimed to identify the preferred LV lead position for upgrading conventional RV apical pacing to CRT.

METHODS

We used electrode catheters positioned at the RV apex and LV anterolateral and posterolateral sites via the coronary sinus (CS) branches to measure the ratio of activation time to QRS duration from the RV apex to the LV anterolateral and posterolateral sites during RV apical pacing. Simultaneous biventricular pacing was performed at the RV apex and each LV site, and the differences in QRS duration and LV dP/dtmax from those of RV apical pacing were measured.

RESULTS

Thirty-seven patients with anterolateral and posterolateral LV CS branches were included. During RV apical pacing, the average ratio of activation time to QRS duration was higher at the LV anterolateral site than at the LV posterolateral site (0.90 ± 0.06 vs. 0.71 ± 0.11, p < .001). The decreasing ratio of QRS duration and the increasing ratio of LV dP/dtmax were higher at the LV anterolateral site than at the posterolateral site (45.7 ± 18.0% vs. 32.0 ± 17.6%, p < .001; 12.7 ± 2.9% vs. 3.7 ± 8.2%, p < .001, respectively) during biventricular pacing compared with RV apical pacing.

CONCLUSION

The LV anterolateral site is the preferred LV lead position in patients being upgraded from conventional RV apical pacing to CRT.

What Body Surface Mapping Has Taught Us About Ventricular Conduction Disease Implications for Cardiac Resynchronization Therapy and His Bundle Pacing

The degree and pattern of conduction disease seem determinant when assessing potential cardiac resynchronization therapy (CRT) candidates. In the present review, the authors discuss the available noninvasive techniques that can be used to acquire ventricular activation time maps. They describe what body surface mapping has taught us about left bundle branch block, right bundle branch block, intraventricular conduction delay, and right ventricular pacing and discuss the ability of derived parameters of electrical dyssynchrony to predict long-term clinical response to CRT or His bundle pacing.

Axis deviation in nonischemic cardiomyopathy with left bundle branch block: Insights from left bundle branch pacing

INTRODUCTION

Biventricular pacing has shown excellent results in patients with heart failure and left bundle branch block (LBBB). Studies have shown that the patients with abnormal axis deviation may benefit less from cardiac resynchronization therapy (CRT) as compared to those with the normal axis. The exact reason for left axis deviation (LAD) in LBBB is not known but could be due to diseased left anterior fascicle, left ventricular enlargement, or due to advanced electrical remodeling.

METHODS

The aim of the study was to analyze the incidence of LAD in nonischemic cardiomyopathy (NICM) with LBBB and the clinical outcomes following left bundle branch pacing (LBBP).

RESULTS

We have included 64 consecutive patients with NICM and LBBB, who underwent successful LBBP. Patients were divided into two groups-Group I with baseline normal axis (n = 40; 63%) and Group II with LAD (n = 24; 37%). The mean axis changed from +23.6 ± 28.8° at baseline to +16.5 ± 35.1° and from -40.4 ± 10.3° at baseline to 7.08 ± 41.1° after LBBP in Group I and Group II, respectively. LBBP retained the normal axis in 93% of Group I patients and normalized the axis in 75% of Group II patients. The percentage changes in QRS duration, left ventricular ejection fraction, and left ventricular end-diastolic diameter were similar in both the groups (+40% vs. +32%; p = .52, +64% vs. +50%; p = 0.34, -8% vs. -6%; p = .76, respectively). Capturing the proximal LBB would correct the LAD by recruitment of left anterior fascicles and pacing proximal to the site of the septal breakthrough of the right bundle branch activation wavefront during LBBB.

CONCLUSION

LBBP as an alternative strategy for CRT could result in similar improvement in LBBB patients with LAD as in those with the normal axis.