Analysis of electrocardiographic signs in hypertrophic cardiomyopathy before and after septal myectomy. New criterion for proximal left bundle branch block

Aim. To analyze 20 electrocardiographic (ECG) signs of left bundle branch block (LBBB) before and after septal myectomy in patients with hypertrophic cardio myopathy (HCM) and develop a criterion for proximal LBBB based on the selected signs. Material and methods. This retrospective non-randomized study included 50 patients with obstructive HCM who underwent septal myectomy. There were following inclusion criteria: QRS width <120 ms before surgery, transaortic access during septal myectomy, and QRS width ≥120 ms in the early postoperative period. For each patient, ECGs were analyzed before septal myectomy and in the first week after surgery. At the same time, 20 ECG signs proposed earlier in the LBBB criteria were independently assessed. Results. Exsection of a small myocardial area of the basal interventricular septal parts, weighing an average of 4,9±2 grams, led to a significant increase in the QRS width (by 61±14,6 ms) and the prevalence of almost all ECG signs of LBBB. In 100% of cases (n=50), the following signs demonstrated significant dynamics after surgery: (1) midQRS notching or slurring in ≥2 contiguous leads (I, aVL, V1-V2, V5-V6); (2) absence of q wave in V5-V6 and (3) discordant T wave in at least two leads (I, aVL, V5, V6). Based on the design of the study, (4) QRS width ≥120 ms was additionally included. These ECG characteristics were combined into a new criterion for proximal LBBB Conclusion. A new criterion for proximal LBBB was developed using the pathophysiological model of iatrogenic conduction block of left bundle branch. Further estimation of this criterion on a set of candidates for CRT with heterogeneous level of LBBB is necessary.