AVNRT Slow/Fast
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
- Main article AVNRT
Overview
The slow/fast variant of AVNRT is the most common variant of AVNRT.
Epidemiology and Demographics
This form of AVNRT accounts for 80%-90% of AVNRT cases.
Diagnosis
EKG
Induction of AVNRT
There are several ways to induce AVNRT.
- The most common way is through the introduction of atrial or ventricular premature depolarizations (APDs and VPDs) beats. You may also need to use double atrial stimuli is you are on the slow pathway.
- Continuous burst pacing or rapid incremental pacing in the right atrium (RA), the coronary sinus (CS) may induce the tachycardia
- Decremental ramp atrial extrastimuli has also been shown to effectively induce AVNRT. to perform this you must set the total number in S1 drive train to one. Turn on S1, S2, S3, S4, S5, and S6 at following cycle lengths: S1—600 ms, S2—550 ms, S3—500 ms, S4—450ms, S5—400 ms, and S6—350 ms. Thus, a train consisting of a total of six APDs at decremental coupling interval of 50 ms from previous APDs are delivered from the HRA. If no SVT is induced, then S1 is programmed at 550 ms and cycle lengths of the subsequent APDs were also decreased by 50 ms, to a minimum of 300 ms.
- If you have no success with the above pacing protocols then you can start pharmacological agents such as isoproterenol or atropine.
- Esmolol has also been reported as useful because it changes the conduction over fast pathway and shortens the refractory period.
- Non-pharmacological maneuvers such as hyperventilation and 45 degree headup upright posture during pacing have also been studied to facilitate induction of AVNRT.
Criteria for Support for AVNRT
- Critical prolongation of the AH interval initiates tachycardia
- Concentric Activation of the atria with the earliest atrial activation at the His bundle or proximal CS and the Septal VA < 65-70 msec.
- Ventricular Overdrive Maneuver results in a value greater than 115 ms
- Delta HA Interval, more postive than -10.
- Development of a BBB with initiation
- Parahisian Pacing results in a Nodal Response
- Decremental VA conduction during programmed Ventricular Stimulation
- Termination by a PVC that was delivered early when the His bundle was not refractory.
Against AVNRT
- Rare to be induced with V pacing
Maneuvers
- PACs. Fail to advance even when early
- PVCs. Fail to advance a when His is refractory
- Ventricular Overdrive Maneuver (PPI-TCL>115)
- V pacing at TCL. Measure VA
Ablation
To ablate AVNRT using an anatomic strategy, you must position your catheter anterior to CS os and have an A/V electrogram proportion of 1/4. The atrial component is usually has multiple components (fractionated) and is rarely sharp. Initial power of 50 W for 60 seconds. With target temperature of 60 degrees. Terminate if no accelerated junctional rhythm occurs after 15 seconds. If junctional rhythm occurs look for VA block and check for antegrade conduction and PR prolongation with rapid atrial pacing (400-500 ms). If unsuccessful may need to ablate superior to the CS os or in CS os. Also can ablate in. Recheck with programmed atrial stimulation after each ablation
Medical Treatment
- Beta Blocker
- Verapamil
- Flecainide 50-200 mg bid
- Propafenone 150 to 300 TID
Sources
- Josephson ME. Supraventricular tachycardia. In: Josephson ME (ed.): Clinical Cardiac Electrophysiology—Techniques and Interpretations,3rd Ed. Philadelphia, Lippincott-Williams and Wilkins, 2002
- Tachycardia and Other Supraventricular Tachycardias BHARAT K. KANTHARIA, M.D., FAROOQ A. PADDER, M.D.,and STEVEN P. KUTALEK, M.D. PACE 2006; 29:1096–1104