Intraventricular Delay and Blocks

Useful Electrocardiographic Signs to Support the Prediction of Favorable Response to Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) is a cornerstone therapeutic opportunity for selected patients with heart failure. For optimal patient selection, no other method has been proven to be more effective than the 12-lead ECG, and hence ECG characteristics are extensively researched. The evaluation of particular ECG signs before the implantation may improve selection and, consequently, clinical outcomes. The definition of a true left bundle branch block (LBBB) seems to be the best starting point with which to select patients for CRT. Although there are no universally accepted definitions of LBBB, using the classical LBBB criteria, some ECG parameters are associated with CRT response. In patients with non-true LBBB or non-LBBB, further ECG predictors of response and non-response could be analyzed, such as QRS fractionation, signs of residual left bundle branch conduction, S-waves in V6, intrinsicoid deflection, or non-invasive estimates of Q-LV which are described in newer publications. The most important and recent study results of the topic are summarized and discussed in this current review.

An S wave in ECG lead V6 predicts poor response to cardiac resynchronization therapy and long-term outcome

BACKGROUND

Cardiac resynchronization therapy (CRT) is a standard treatment for selected patients with chronic heart failure (HF). However, up to 30%-50% of patients still do not respond to CRT.

OBJECTIVE

Our aim was to identify the predictive value of an S wave in lead V₆ in CRT response in patients with complete left bundle branch block (CLBBB).

METHODS

The CLBBB definition included the Strauss left bundle branch block criteria and the absence of q waves in leads I, V₅, and V₆. According to the electrocardiogram at baseline, CLBBB patients were divided into 3 groups: T-CLBBB group (CLBBB without an S wave in lead V₅ or V₆), V₅S group (CLBBB with an S wave in lead V₅ and no S wave in lead V₆), and V₅&V₆S group (CLBBB with S waves in leads V₅ and V₆). CRT response was defined as left ventricular end-systolic volume reduction ≥ 15% at 6-month follow-up. The combined end point included HF rehospitalization or all-cause death.

RESULTS

Of 181 patients with left bundle branch block-like pattern, 112 patients with CLBBB were included into 3 groups: 54 in the T-CLBBB group, 32 in the V₅S group, and 26 in the V₅&V₆S group. The CRT response rate was 85.2% (46), 65.6% (21), and 38.5% (10), respectively (P < .001). Kaplan-Meier curves demonstrated that patients in the V₅&V₆S group had a higher incidence of HF rehospitalization or all-cause death than those in the other 2 groups (P < .001). In a multivariate logistic regression model analysis, an S wave in lead V₆ was significantly associated with CRT nonresponse (hazard ratio 0.33; 95% confidence interval 0.11-0.96; P = .042).

CONCLUSION

An S wave in lead V₆ can predict poor response to CRT and long-term outcome.

Osteogenic circulating endothelial progenitor cells are linked to electrocardiographic conduction abnormalities in rheumatic patients

BACKGROUND

Osteogenic circulating endothelial progenitor cells (EPC) play a pathogenic role in cardiovascular system degeneration through promulgating vasculature calcification, but its role in conduction disorders as part of the cardiovascular degenerative continuum remained unknown.

AIM

To investigate the role of osteocalcin (OCN)-expressing circulating EPCs in cardiac conduction disorders in the unique clinical sample of rheumatoid arthritis (RA) susceptible to both abnormal bone metabolism and cardiac conduction disorders.

METHODS

We performed flow cytometry studies in 134 consecutive asymptomatic patients with rheumatoid arthritis to derive osteogenic circulating OCN-positive (OCN+) CD34+KDR+ vs. CD34+CD133+KDR+ conventional EPC. Study endpoint was the prespecified combined endpoint of electrocardiographic conduction abnormalities.

RESULTS

Total prevalence of cardiac conduction abnormality was 9% (n = 12). All patients except one had normal sinus rhythm. One patient had atrial fibrillation. No patient had advanced atrioventricular (AV) block. Prevalence of first-degree heart block (>200 ms), widened QRS duration (>120 ms) and right bundle branch block were 6.7%, 2.1%, and 2.2% respectively. Circulating osteogenic OCN⁺ CD34⁺ KDR⁺ EPCs were significantly higher among patients with cardiac conduction abnormalities (p = 0.039). Elevated OCN⁺ CD34⁺ KDR⁺ EPCs> 75th percentile was associated with higher prevalence of cardiac conduction abnormalities (58.3% vs. 20.02%, p = 0.003). Adjusted for potential confounders, elevated OCN⁺ CD34⁺ KDR⁺ EPCs> 75th percentile remained independently associated with increased risk of cardiac conduction abnormalities (OR = 4.4 [95%CI 1.2-16.4], p = 0.028). No significant relation was found between conventional EPCs CD34+CD133+KDR+ and conduction abnormalities (p = 0.36).

CONCLUSIONS

Elevated osteogenic OCN⁺ CD34⁺ KDR⁺ EPCs are independently associated with the presence of electrocardiographic conduction abnormalities in patients with rheumatoid arthritis, unveiling a potential novel pathophysiological mechanism.