Intraventricular Conduction Delay and Mortality in Acute Coronary Syndrome

Nonspecific intraventricular conduction delay (NIVCD) is a significant predictor of mortality among patients with acute coronary syndrome (ACS), but this risk is not associated with left ventricular ejection fraction (LVEF). Left bundle branch block (LBBB) is another high-risk factor predicting mortality in this population and is associated with LVEF, however it remains unclear how significant right bundle branch block (RBBB) is as a high-risk factor for death among patients with ACS, according to study findings published in the European Heart Journal Acute Cardiovascular Care.

Investigators sought to determine if a diagnosis of intraventricular conduction delay (IVCD; RBBB, LBBB, or NIVCD) in patients with ACS is related to long-term prognosis. The primary endpoint was cardiac death.

They conducted a retrospective study of 9749 consecutive patients with an invasive coronary angiography diagnosis of ACS and a recorded electrocardiogram (ECG) who were evaluated from January 2007 through December 2018 at Tays Heart Hospital in Finland. Follow-up for cardiac-related death was through December 2020. The Finnish national register was searched for mortality and cause of death data with no losses to follow-up.

Patients (mean age, 68.3±11.8 years; 32.7% women) had a median follow-up time of 6.1 years (IQR, 3.3-9.4).  In follow-up, there were 3156 deaths, of which 52.9% were cardiac-related. A total of 8681 patients (89.1%) did not have IVCD. There were 239 patients with NIVCD, 288 patients with LBBB, and 539 patients with RBBB. Compared with patients with no observable conduction disorders, patients with IVCD tended to be older at baseline with more comorbidities.

There were 551 deaths among patients with IVCDs. Overall, 76.9% of patients with NIVCD, 67.6% of patients with LBBB, 55.7% of patients with RBBB, and 50.1% of patients with no IVCD died. The investigators noted that in the first 12 years of follow-up, cumulative incidence for cardiac death was 19.6% among patients with no IVCD, 57.0% among patients with NIVCD, 46.2% among patients with LBBB, and 33.2% among patients with RBBB (all P <.001 for comparison). At 12 years, cumulative incidence for other causes of death was 21.9% among patients with no IVCD, 19.7% among patients with NIVCD, 22.6% among patients with LBBB, and 29.1% among patients with RBBB.

Patients in all IVCD groups had a significantly higher risk of cardiac death vs patients with no IVCD (NIVCD subdistribution hazard estimate [SDH], 2.68; 95% CI, 2.19-3.27; LBBB SDH, 1.63; 95% CI, 1.31-2.03; P <.0001; RBBB SDH, 1.37; 95% CI, 1.15-1.64; P <.0001). NIVCD and RBBB remained notable risk factors for cardiac death after adjusting for LVEF (hazard ratio [HR], 1.96; 95% CI, 1.59-2.43; P <.001 for NIVCD; and HR, 1.30; 95% CI, 1.08-1.56; P =.005 for RBBB).

Study limitations include exclusion of noninvasively diagnosed patients and the older age of patients with IVCD.

Among consecutive patients receiving invasive evaluation for ACS, investigators concluded those with NIVCD were a high-risk subgroup compared with other patients. “In contrast to LBBB, the risk associated with NIVCD was not related to LVEF.” Investigators believe NIVCD should be acknowledged in guidelines as a significant predictor of death. They wrote, “Our results support the ESC guidelines describing LBBB in patients as a high-risk feature, but a matter of debate remains in whether RBBB should be considered as a high-risk factor not only in STEMI but also in ACS patients.”