Define HV interval and its clinical implication when prolonged.

• A. HV interval is the conduction time from His bundle to the ventricular myocardium; prolongation suggests His-Purkinje disease and potential need for pacing.
• B. HV interval measures atrioventricular nodal conduction time, and prolongation indicates AV block.
• C. HV interval is the time from left ventricle to right ventricle and prolongation indicates bundle branch block.
• D. HV interval is the time from atrial activation to ventricular activation and prolongation indicates AV nodal delay.

Answer: (A)

The HV interval reflects conduction time through the His-Purkinje system, specifically from the His bundle to the onset of ventricular activation. Normal HV is typically in the range of about 35 to 55 milliseconds in adults. When this interval is prolonged, it points to disease in the infra-Hisian portion of the conduction system (below the AV node), meaning there’s a delay or block within the His-Purkinje network.

Clinically, a prolonged HV interval signals a higher risk of progression to higher-grade AV block. In patients who are symptomatic or have structural heart disease, this finding often leads to considering pacing therapy to prevent dangerous bradyarrhythmias.

The other interpretations don’t fit HV because the PR interval measures AV nodal conduction time, not the His-Purkinje pathway; the time between ventricles or a concept like left-to-right ventricular conduction isn’t what HV represents; and AV nodal delay is reflected by the PR interval, not HV.