Non-specific intraventricular conduction delay

ECG: Sinus activity with left atrial enlargement (widened P wave, wide negative component in V1); non-specific block (wide QRS > 120 ms, without the typical pattern of right bundle branch block or left bundle branch block);

Comments: This tracing corresponds to a non-specific intraventricular conduction delay  pattern. This is a diagnosis of elimination in the presence of a wide QRS (> 120 ms) while not displaying the characteristics of a right bundle branch block or left bundle branch block. It is therefore not possible to define a characteristic pattern. The pathophysiology of this conduction disorder is complex but nonetheless reflects the presence of a global alteration of cardiac conduction. It is therefore not a bundle branch block but rather a distal disturbance of ventricular conduction. Indeed, conduction is normally achieved in the nodo-Hisian conduction pathways but is slowed in a diffuse manner in the ventricular myocardium. This type of conduction delay corresponds to various clinical and electrophysiological presentations although prognosis is somewhat poor and predominantly observed in patients with ischemic cardiomyopathy or hypertrophic cardiomyopathy.

In this patient, the electrocardiogram corresponds to an “enlarged” left anterior fascicular block pattern: left axis, qR pattern in lead I, rS in leads II, III, q waves and poor R wave progression in right-side precordial leads, wide S wave in V6.

Take-home message: Non-specific intraventricular conduction delay corresponds to a widening of the QRS complex without the characteristic pattern of right or left bundle branch block; it is therefore a diagnosis of elimination.