What is the normal H-V (His-ventricular) interval during electrophysiology (EP) testing for conduction disease?

Normal H-V Interval During Electrophysiology Testing for Conduction Disease

The normal H-V interval during electrophysiology (EP) testing ranges from 35 to 55 milliseconds, with values ≥70 ms considered abnormal and indicative of infranodal conduction disease requiring permanent pacing in symptomatic patients. 1

Understanding the H-V Interval

The H-V interval represents the conduction time from the His bundle to ventricular activation and is a critical measurement during EP studies for evaluating conduction disorders. This measurement helps assess infranodal conduction and identify patients at risk for developing complete heart block.

Normal and Abnormal Values:

• Normal range: 35-55 milliseconds
• Borderline: 56-69 milliseconds
• Abnormal: ≥70 milliseconds

Clinical Significance and Management

When H-V Interval is ≥70 ms:

• In patients with syncope and bundle branch block with HV interval ≥70 ms, permanent pacing is recommended (Class I recommendation) 1
• This finding indicates significant infranodal conduction disease with increased risk of progression to complete heart block

When H-V Interval is Normal:

• Patients with normal H-V intervals have a lower risk of progression to complete heart block
• The risk of progression of conduction disease is relatively low with either normal or prolonged H-V intervals during short-term follow-up 2

Special Considerations

Bundle Branch Block:

• The HV interval in patients with bifascicular block measures conduction time through the remaining functioning fascicle 1
• Patients with bifascicular block and prolonged HV interval (>55 ms) have a slightly increased risk of developing complete trifascicular block 1
• Despite high prevalence of prolonged HV intervals in these patients, the annual incidence of progression to complete trifascicular block is only 2-3% 1

Risk Stratification:

• HV interval has high sensitivity (82%) but low specificity (63%) for predicting development of complete trifascicular block 1
• In patients with bundle branch block and unexplained syncope, approximately 50% will have clinically significant abnormalities on EP testing, including HV ≥70 ms 3

Prognostic Value:

• Some studies question the prognostic value of HV interval alone in predicting progression to permanent AV block 4
• However, ACC/AHA/HRS guidelines still recommend permanent pacing for patients with syncope and bundle branch block who have HV interval ≥70 ms 1

Clinical Algorithm for H-V Interval Interpretation

1. H-V <55 ms: Normal conduction - no specific intervention needed
2. H-V 56-69 ms: Borderline - consider clinical context and other risk factors
3. H-V ≥70 ms:
   • With syncope/symptoms: Permanent pacing recommended (Class I) 1
   • Without symptoms: Clinical monitoring recommended, permanent pacing not indicated in asymptomatic patients with isolated conduction disease and 1:1 AV conduction 1
4. H-V >100 ms: Highest risk for progression to complete heart block, even in asymptomatic patients

Common Pitfalls

• Relying solely on H-V interval without considering clinical symptoms
• Premature permanent pacemaker implantation when conduction disturbances may be transient
• Failure to recognize that some patients with prolonged H-V intervals may never progress to complete heart block
• Not considering other causes of syncope in patients with bundle branch block (e.g., vasodepressor mechanisms)

The H-V interval remains a valuable tool in the assessment of conduction disorders, but should be interpreted within the broader clinical context of the patient's symptoms and other electrophysiologic findings.