Vectorcardiography – ABC CARDIOL

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Editorial

The Importance of Electrovectorcardiographic Assessment of Intraventricular Blocks and their Relationship with the Cardiac Cycle

The impact of intraventricular conduction disorders on myocardial activation and ventricular function has long been debated. However, with the advent of cardiac resynchronization therapy, this topic has gained even more attention during the last two decades.^,

At that time, our team utilized surface electrocardiographic mapping and isochronal line maps to assess the mean activation time in three specific regions of the heart: the right ventricle (RV), the left ventricle (LV), and the anteroseptal region. This evaluation was conducted on patients with a left ventricular ejection fraction of less than 40%, who exhibited left bundle branch block (LBBB), and had a mean QRS duration of 180 ms.^, The cardiac electrical activation was evaluated in three groups of patients: 1) patients with native LBBB, 2) patients under RV pacing, and 3) patients under biventricular pacing (BVP). In individuals with LBBB, the RV and anteroseptal mean activation time were delayed compared to the LV, leading to a loss of synchrony. Similarly, the RV pacing group’s activation time extended beyond normal, with a more significant difference between the septal area and LV. LV and RV activation times were similar during BVP, and the septal activation approached the normal and native LBBB conditions. Those findings suggested that the prolonged RV electrical activation by BVP, which sometimes may go unnoticed in the presence of LBBB, could be a relevant criterion in selecting candidates for cardiac resynchronization therapy.^,

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Original Article

Impact of Intraventricular Blocks on Cardiac Cycle Dynamics: An Echocardiographic and Vectorcardiographic Analysis

Carlos Eduardo Duarte et al. Katia Regina Silva Luciene Dias de Jesus Henry Abensur Roberto Costa

Abstract

Background

Left bundle branch block (LBBB) causes delays that alter the mechanics of the ventricular cycle. The effect of other intraventricular blocks (IVB) remains little explored.

Objectives

To study the phases of the cardiac cycle (CC) and ventricular synchrony in different ventricular activation patterns.

Methods

Cross-sectional study with 328 consecutive individuals without structural heart disease, normal electrocardiogram or IVB, conducted in the period between August/2020 and January/2022. Echocardiogram and Vectorcardiogram were performed simultaneously to analyze the electromechanics of the CC. A one-way Analysis of Variance (ANOVA) with Bonferroni’s multiple comparison test was used, with a significance level of 5%.

Results

The age of the participants was 64.8±15.3 years, with 57.9% male and an ejection fraction of 67.0±6.8%. The electrocardiogram was normal for 32.3%, 18.6% had right bundle branch block (RBBB), 17.7% had left anterior fascicular block (LAFB), 15.6% had RBBB+LAFB, and 15.9% had LBBB. The echocardiogram showed an increased left ventricular pre-ejection by 18.7% (p<0.001) and 56.8% (p<0.001) in RBBB+LAFB and LBBB, respectively. There was a post-systolic myocardial contraction in all types of IVB and ventricular dyssynchrony in LBBB. Using the vectorcardiogram, initial activation of the R wave was increased by 17.4% in LAFB (p<0.001), 43.5% in RBBB+LAFB (p<0.001) and 47.4% in LBBB (p<0.001) and delayed final activation by 69.4% in LBBB (p<0.001), 73.6% in RBBB+LAFB (p<0.001) and 95.3% in RBBB (p<0.001).

Conclusion

All IVBs modified the CC; however, only LBBB and RBBB+LAFB significantly changed the left ventricular cycle, thereby evidencing the greater complexity of these disorders.