What will you learn?
- what is AH and HV intervals
- how to measure both correctly
- what are the normal ranges
- what is the clinical relevancy of this parameter
About this scenario
- AH and HV intervals are the basic measurements of AV conduction.
- The AH interval reflects the AV node antegrade conduction time (from when the impulse enters the AV node to when it exits it) and it is measured from the onset of periAV node atrial activation to the onset of the earliest His-bundle electrogram.
- The HV interval reflects the His-Purkinje system antegrade conduction time (from when the impulse gets into the His bundle to when it exists into the ventricles) and it is measured from the onset of the earliest His bundle electrogram to the earliest ventricular activation, whether it is apparent on the surface ECG or on intracardiac recordings.
- The normal value of the AH interval ranges from 50 to 150 ms. It is prolonged due to vagal hypertonia, ionic disturbances, drugs or structural damage to the AV node. It is shortened if there is a hyper conductive AV node or, very rarely, an atriohisian accessory pathway. The AH interval also physiologically prolongs with rapid atrial pacing.
- The normal value of the HV interval ranges from 35 to 55 ms. It is prolonged up to 65 ms in the presence of left bundle-branch block and even more if there are ionic disturbances, drugs or damage to the His-Purkinje conduction, such as in Lenegre and Lev diseases. It is shortened in there are accessory structures to the normal His-Purkinje system that allow a faster conduction from the atria (AV accessory pathways) or the His-Purkinje system (fasciculoventricular accessory pathways) to the ventricles. The HV interval physiologically remains constant and does not prolong or block with rapid atrial pacing except in some young individuals at very high rates.
