As we covered in Part I, our patient was experiencing the life threatening combination of Wolff-Parkinson-White (WPW) and atrial fibrillation.
The EMS 12-Lead Blog team broke this conclusion up into two parts due to the importance of understanding this particular dysrhythmia. The patient survived in spite of the treatment provided, however, with the proper education both in-hospital and pre-hospital providers can rapidly identify and appropriately treat WPW and atrial fibrillation!
We also discussed that the danger in this arrhythmia is that the AV node no longer provides an effective "speedbump" for the barrage of atrial impulses. Any treatments which further slow or block the AV node without also slowing or blocking the accessory pathway will likely be lethal.
Thankfully, there are some key findings in WPW and AF which pre-hospital providers can use to identify this arrhythmia:
- Bizarre, constantly changing morphologies due to varying preexcitation
- If the rate meets or exceeds 300 bpm, or less than or equal to one large box, an accessory pathway must exist
- If the rate exceeds 260 bpm, you can be confident an accessory pathway exists
- If the rate exceeds 220 bpm, you need to be suspicious of an accessory pathway
Remember, slowing down the AV node in patients with uncontrolled atrial foci–such as atrial fibrillation or flutter–can be lethal! Stick with cardioversion or procainamide. The following, striking 12-Lead is from a 59 year old female with palpitations (from the amazing Harvard WaveMaven case files):
Once you've seen it, you can't forget it!
However, as noted in Part I, not every patient with an accessory pathway will present with atrial fibrillation. Often they will present with a regular supraventricular tachycardia with either a narrow or a wide complex.
In the case of a regular, wide complex rhythm without discernable atrial activity treat as per ventricular tachycardia. However, it bears repeating that at rates exceeding 220 bpm an accessory pathway may be present, so avoid lidocaine and amiodarone and favor procainamide or cardioversion.
In the case of a regular, narrow complex rhythm treat as per SVT. Some of these patients may be very young, however, this should not keep you from treating them if they are unstable.
Adenosine is safe and effecacious for the treatment of SVT in children. However, vagal maneuvers can be particularly successful. With infants you can place an ice pack on the bridge of their nose to stimulate a vagal response. In older children ask them to blow through a small syringe or straw.
- Accessory pathways, like WPW, can cause conduction rates to exceed 250 bpm and sometimes exceed 300 bpm
- Without the speed limits imposed by the AV node, accessory pathways which receive no innervation to control them may allow lethal arrhythmias with the drugs
- Cardioversion is a safe and effective treatment for unstable or potentially unstable tachyarrythmias such as WPW and atrial fibrillation