Delta HA Interval
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- Useful to differentiate AVNRT from Orthodromic Reciprocating Tachycardia using a posterior septal bypass tract since the sequence of His bundle and atrial activation are fundamentally different in AVNRT versus Orthodromic Reciprocating Tachycardia using a posterior septal bypass tract.
- His - Atrial Activation during SVT
- During AVNRT impulses are already traveling back up the retrograde limb of the AV nodal circuit at the same time the His is activated (parallel activation), whereas the His and atrium are activated sequentially (series activation) in Orthodromic Reciprocating Tachycardia using a posterior septal bypass tract.
- His - Atrial Activation during Ventricular Pacing
- During AVNRT the His bundle and atrium are activated in series and in Orthodromic Reciprocating Tachycardia using a posterior septal bypass tract the His bundle and atrium are activated in parallel
| Maneuver | AVNRT | ORT |
| Mean SVT HA | 104 ms | 241 ms |
| Mean Paced HA | 127 ms | 151 ms |
| Mean Delta HA | 21 | -85 |
- How to perform maneuver
- Measure the HA interval in tachycardia
- Measure the HA interval with Ventricular pacing
- Calculate Delta HA interval which is HA PACED - HA SVT
- Delta HA more negative than -10 are always Orthodromic Reciprocating Tachycardia using a posterior septal bypass tract.
- Delta HA more postive than -10 are always AVNRT
- How to perform maneuver if there is you can not identify a retrograde His during Ventricular pacing
- Measure the HA in tachycardia which can be measured in all patients
- Measure VA interval with ventricular pacing
- Calculate the HA SVT - VA pacing
- The mean delta was -89 in the ORT group and 17 in the AVNRT
- A Value more negative than -40 ms suggest AVNRT
- A Value more postive than -40 suggest ORT
References
- Usefullness of delta HA interval to accuratelt distinguish AVNRT from ORT Septal BT Tachycardias. Miller J et al. Am J Cardiol 1991:68:1037-1044
