Diagnostic Value of Slow Conduction Index in Differential Diagnosis of Wide QRS Complex Arrhythmias with Left Bundle Branch Block Morphology

BACKGROUND: Differential diagnosis of arrhythmias with wide QRS complexes remains an unresolved problem in clinical practice. After decades of careful research, many different criteria and algorithms have been proposed, but many of them are not quite accurate and effective in real clinical conditions. One of the approaches is to use ECG to estimate the speed of propagation of excitation through the ventricular myocardium. The estimation is based on the ratio of the amplitudes of the initial and final parts of the QRS complex, in particular, using the slow conduction index. AIM: To study the possibility of using the slow conduction index in the differential diagnosis of arrhythmias with wide QRS complexes and to carry out a detailed comparative analysis of the diagnostic value of this criterion in all 12 ECG leads with evaluation and comparison of the obtained values of diagnostic accuracy. MATERIALS AND METHODS: The study included 280 single wide QRS complexes with a form of left bundle branch block (LBBB) detected during one-day and multi-day ECG monitoring in randomly selected 28 patients. For a detailed analysis, a comparison of the original 12-lead ECG and individual scalable ECG graphs for selected leads was carried out, followed by measurement of the absolute values of the total amplitudes during the initial and final 40 ms wide QRS complexes. For a qualitative and quantitative assessment of diagnostic significance, ROC analysis was used to determine the informative value of a diagnostic test based on sensitivity (Sn), specificity (Sp) and diagnostic accuracy (Acc). RESULTS: According to the obtained values of Sn, Sp and Acc, all 12 leads were arranged in the following order as the diagnostic value of the slow conduction index decreased: aVL, V2, aVF, V5, III, V1, V4, II, aVR, V6, V3 and I. In the first six ECG leads, Acc was consistently above 90%, gradually decreasing in the next six leads from 89% to 67%, respectively (p 0.001 for all leads). CONCLUSIONS: The results of this study showed that the slow conduction index can be used in any ECG leads as a criterion for the differential diagnosis of arrhythmias with wide QRS complexes with a form of LBBB. The study also demonstrated the importance of a comprehensive approach to the analysis of the form of the QRS complex and the need for a consistent detailed analysis of the existing criteria for the differential diagnosis of arrhythmias with wide QRS complexes in different clinical groups of patients.