Nonspecific intraventricular conduction delay

A nonspecific intraventricular conduction delay exists if the ECG displays a widened QRS appearance that is neither a left bundle branch block (LBBB) nor a right bundle branch block (RBBB). The QRS morphology of nonspecific intraventricular conduction delays may vary substantially.

Definition and causes of nonspecific intraventricular conduction delay

According to the American Heart Association/American College of Cardiology and the Heart Rhythm Society (AHA/ACCF/HRS) recommendations, a nonspecific intraventricular conduction delay is defined as “a QRS duration greater than 110 ms in adults, greater than 90 ms in children 8 to 16 years of age, and greater than 80 ms in children less than 8 years of age without meeting the criteria for RBBB or LBBB.”

These conduction delays may be observed after large myocardial infarctions, in which the large necrotic area may cause nonspecific conduction disturbances. Such conduction disturbances may also be superimposed on existing bundle branch blocks and alter their appearance.

Some patients develop nonspecific intraventricular conduction defects without any change in their QRS appearance. Such conduction delays may be due to myocardial fibrosis, amyloidosis, cardiomyopathy or hypertrophy.

Prognosis of nonspecific intraventricular conduction delay

Patients with nonspecific intraventricular conduction delays are at twice as great a risk of all-cause death and cardiovascular death, compared to patients without such disturbances, including those with RBBB and LBBB. This was reported in the Coronary Heart Disease Study,1 which enrolled 10,899 participants with baseline ECG examinations. Individuals with nonspecific intraventricular conduction delays were at particularly high risk of death due to arrhythmias.

Note that other causes of wide QRS complex must always be considered. For example, Wolff-Parkinson-White syndrome (WPW), pacemaker-stimulated beats, electrolyte imbalance and medications may prolong the QRS complex.

References

1. Aro AL, Anttonen O, Tikkanen JT, et al. Intraventricular conduction delay in a standard 12-lead electrocardiogram as a predictor of mortality in the general population. Circ Arrhythm Electrophysiol 2011;4:704–710.
2. Eschalier R et al. Heart Rhythm. 2015 May;12(5):1071-9. Nonspecific intraventricular conduction delay: Definitions, prognosis, and implications for cardiac resynchronization therapy.