Do not overlook critical warnings

• what are critical warnings during AVNRT ablation
• when it is most likely that something can go wrong
• how to avoid putting patient in danger

​

Like any medical procedure also AVNRT ablation can go wrong. The best way to avoid it is to look for a really good signal to start your ablation. For that revisit previous lesson. In this lesson your task is to observe warning signs and avoid it in real life.

Typical warning signs:

• During ablation, the occurrence of fast junctional rhythm indicates proximity to the AV node. As slow and regular junctional beats are welcome during ablation a sudden acceleration and short CL (start worrying below 400ms and STOP ablation below 350ms) between junctional beats is a warning sign.
• Loss of VA conduction during junctional beats is also a typical signal to stop ablation and start praying. It’s not easy to spot but you need to train your eye for it. Look for the signal characteristics of junctional beat complex (V and A) and if you spot a missing A component stop immediately. Hopefully you will more frequently stop because of PVC caused by catheter movement into RV which appear without A but it’s a good sign you are paying attention to those small details.
• Prolongation of AV conduction is a fatal sign during ablation. It will appear most likely in sinus rhythm and not during junctional beats (but it is also possible). The easiest way to notice it is to observe carefully the AV interval at CS channel. Any sign of prolongation should be consider a warning.

When I’m putting my patient in danger without realizing it:

• Ablation during ongoing AVNRT is very tricky as it all happens very quickly and the intervals and signals are frequently hard to distinguish. Moreover, fast junctional beats proceeding an AV block can be easily overlooked. Therefore, it is advisable to ablate during sinus rhythm.
• If patient is moving or breathing heavily because of stress or pain during procedure a risk of catheter dislodgment is quite high. It is a good practice to advise the patient about what is going to happen, that he or she will probably experience a short episode of chest pain and should stay calm or inform the operator.
• Sometimes you might see in fluoroscopy or 3D mapping system or even feel an unexpected catheter movement caused by heart contraction. In such case it is advisable to stop ablation and assess new signals without ablations artefacts.
• What you want to definitely avoid is ablating already non-inducible patient. You might think that previous ablation attempts were not sufficient and you need to burn a little bit more but you might be wrong. It costs you nothing to stop for a second and try induction maneuvers. Maybe you are lucky and you already modulated a slow pathway so it can not sustain arrhythmia.

How to minimalize the risky:

• Using low power and temperature settings during radiofrequency ablation can reduce the risk of unintended damage. Ablation typically starts at 20-30 Watts, and careful titration of energy is necessary to prevent collateral damage to the AV node. Gradually increasing the energy delivery while monitoring for adverse effects can prevent sudden, unexpected damage to the AV node.
• A quick pull back of the ablation catheter and not only switching off ablation is your best response to any critical warning. Consider that even after cessation of impulse the tip of the catheter is still hot and further damage can occur. Therefore, you want to physically disconnect catheter form the tissue.
• If every ablation attempt triggers AVNRT you might consider intraprocedural admission of low dose betablocker in order to “cool down” the induction of arrhythmia and conduct ablation at sinus rhythm.
• When the unfortunate happens and you see the damage to the AV node either in form of AV conduction prolongation or block you might consider admission of prednisolone in order to reduce tissue inflammation that might increase the damage. Remember that the conduction block can reappear even hours after acute damage as the tissue edema grows and compress AV node tissue. Therefore, a sufficient monitoring is necessary.