Redefining left bundle branch block from high-density electroanatomical mapping
Jun-Hua Zou1, Bao-Tong Hua2, Xiao-Xia Shao2
1The first Department of Cardiology, the First Affiliated Hospital of Kunming Medical University, Kunming, Yunnan, China.
Insights
Existing electrocardiogram (ECG) criteria for left bundle branch block (LBBB) lack accuracy. Measuring the notch width to left ventricular diameter ratio (Nw/LVd) improves diagnosis of true LBBB.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Diagnostics
Background:
- Current electrocardiogram (ECG) criteria for diagnosing left bundle branch block (LBBB) are insufficient for accurate differentiation between true and false blocks.
- Distinguishing true LBBB from LBBB-like patterns is crucial for appropriate patient management and treatment, particularly in cardiac resynchronization therapy (CRT) candidates.
Purpose of the Study:
- To investigate the utility of QRS notch width in lateral leads as a supplementary diagnostic marker for true complete left bundle branch block (t-LBBB).
- To evaluate the diagnostic performance of the notch width to left ventricular end-diastolic diameter (Nw/LVd) ratio in differentiating t-LBBB from false LBBB (f-LBBB).
Main Methods:
- Utilized high-density, 3D electroanatomical mapping in 37 CRT patients with LBBB-like ECGs.
- Defined t-LBBB and f-LBBB based on the presence or absence of left bundle branch potentials from base to apex.
- Compared clinical characteristics, electrical excitation spread, QRS notch width, and Nw/LVd ratio between t-LBBB and f-LBBB groups.
- Performed ROC analysis to determine the sensitivity and specificity of Nw/LVd for diagnosing t-LBBB.
Main Results:
- Twenty-five patients were classified as t-LBBB and 12 as f-LBBB.
- Distinct patterns of QRS notch depolarization were observed between t-LBBB and f-LBBB groups.
- The Nw/LVd ratio showed a statistically significant difference between the groups (0.65 ± 0.19 ms/mm vs. 0.81 ± 0.17 ms/mm, P < 0.05).
- ROC analysis yielded a sensitivity of 56% and a specificity of 91.7% for diagnosing t-LBBB using the Nw/LVd ratio.
Conclusions:
- The Nw/LVd ratio serves as a valuable quantitative marker to enhance the diagnostic accuracy of LBBB.
- Incorporating the Nw/LVd measurement into existing ECG criteria can improve the identification of true LBBB.
Background:
The existing ECG criteria for diagnosing left bundle branch block (LBBB) are insufficient to distinguish between true and false blocks accurately.
Methods:
We hypothesized that the notch width of the QRS complex in the lateral leads (I, avL, V5, V6) on the LBBB-like ECG could further confirm the diagnosis of true complete left bundle branch block (t-LBBB). We conducted high-density, three-dimensional electroanatomical mapping in the cardiac chambers of 37 patients scheduled to undergo CRT. These patients' preoperative electrocardiograms met the ACC/AHA/HRS guidelines for the diagnosis of complete LBBB. If the left bundle branch potential could be mapped from the base of the heart to the apex on the left ventricular septum, it was defined as a false complete left bundle branch block (f-LBBB). Otherwise, it was categorized as a t-LBBB. We conducted a comparative analysis between the two groups, considering the clinical characteristics, real-time correspondence between the spread of ventricular electrical excitation and the QRS wave, QRS notch width of the lateral leads (I, avL, V5, V6), and the notch width/left ventricular end-diastolic diameter (Nw/LVd) ratio. We performed the ROC correlation analysis of Nw/LVd and t-LBBB to determine the sensitivity and specificity for diagnostic authenticity.
Results:
Twenty-five patients were included in the t-LBBB group, while 12 patients were assigned to the f-LBBB group. Within the t-LBBB group, the first peak of the QRS notch correlated with the depolarization of the right ventricle and septum, the trough corresponded to the depolarization of the left ventricle across the left ventricle, and the second peak aligned with the depolarization of the left ventricular free wall. In contrast, within the f-LBBB group, the first peak coincided with the depolarization of the right ventricle and a majority of the left ventricle, the second peak occurred due to the depolarization of the latest, locally-activated myocardium in the left ventricle, and the trough was a result of delayed activation of the left ventricle that did not align with the usual peak timing. The QRS notch width (45.2 ± 12.3 ms vs. 52.5 ± 9.2 ms, P < 0.05) and the Nw/LVd ratio (0.65 ± 0.19 ms/mm vs. 0.81 ± 0.17 ms/mm, P < 0.05) were compared between the two groups. After conducting the ROC correlation analysis, a sensitivity of 56% and a specificity of 91.7% for diagnosing t-LBBB using Nw/LVd were obtained.
Conclusion:
By utilizing the current diagnostic criteria for LBBB, an increased Nw/LVd value can enhance the effectiveness of diagnosing LBBB.
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