Electrocardiogram abnormalities in left bundle branch block and out-of-hospital cardiac arrest.

Background: Left bundle branch block (LBBB) can be a marker of cardiovascular risk. This study investigates how electrocardiogram (ECG) measurements can be utilized in risk stratification of LBBB patients.

Methods: Using registry data from the Copenhagen General Practitioners Laboratory, first-time LBBB ECGs were identified from 2001 to 2015. Different ECG parameters were extracted including P-wave duration, PR interval, QRS duration, QRS area, QTc, JTc intervals and heart rate. Data were stratified according to the median values of these parameters (below vs above). The outcome was out-of-hospital cardiac arrest (OHCA), and the crude 5-year risk of OHCA was calculated for each subgroup. Multivariable Cox proportional hazards regression was employed to assess associations of ECG parameters with OHCA.

Results: We identified 4644 patients with incident LBBB contributing to a combined 35,113 person-years follow-up (median age 75 [25th - 75th percentiles 66-83] years; male sex, 62 %). Over the study period, all-cause mortality was 50 % and 4 % reached the primary outcome. The crude 5-year risk of OHCA revealed significant associations for QRS duration >150 ms (p = 0.01) and JTc duration >317 ms (p = 0.03). Multivariable analysis showed a higher hazard ratio (HR) for OHCA associated with QRS duration >150 ms (HR 1.41 [95 % CI 1.06-1.88]), QTc duration >464 ms (HR 1.43 [95 % CI 1.08-1.90]), JTc duration >317 ms (HR 1.50 [95 % CI 1.13-2.00]) and heart rate > 72/min (HR 1.48 [95 % CI 1.12-1.97]).

Conclusion: This study provides insights into associations between specific ECG parameters and the risk of OHCA in patients with LBBB. This holds the potential for risk stratification and targeted intervention in this population, and individuals with LBBB and these specific ECG abnormalities might benefit from earlier referral to investigation by specialists.