Dr. Tom Colletti DHSc, PA-C, DFAAPA
A typical cardiac electrical impulse originates in the SA node and propagates to the AV node down the interventricular septum. Variations in this electrical impulse are found when patients are born with an accessory pathway, which is an extra piece of heart muscle tissue that directly connects the atria and ventricles. Accessory pathways cause premature activation of the ventricles, commonly referred to as preexcitation syndrome. Wolff-Parkinson-White (WPW) Syndrome is a common example of a preexcitation syndrome and is a combination of accessory pathway activation and episodes of tachycardia. The preexcitation syndrome seen with WPW can be divided into orthodromic and antidromic activation. The difference between the two relies on the ventricles being activated exclusively by the accessory pathway (antidromic) or being activated in combination with the accessory pathway and the normal activation pathway (orthodromic). The difference can be seen on an EKG with a widened QRS in antidromic activation versus a normal QRS in orthodromic activation. The clinical relevance of WPW and what activation is present are seen with the variations in treatment. One factor with treatment that does not vary with the type of activation is the hemodynamic stability of the patient, in any instability the primary treatment is rapid cardioversion. In orthodromic activation, where the QRS is a narrow complex, the treatment is similar to SVT with the initial treatment being Valsalva maneuvers followed by AV nodal blocking agents. In antidromic activation, the preferred treatment is procainamide. While AV nodal blocking agents are a preferred treatment in orthodromic activation they can be potentially dangerous in antidromic activation. In patients with suspected antidromic activation, these agents may encourage activation down the accessory pathways which accelerate ventricular rates causing an increased risk for ventricular fibrillation. Providing education on the accessory pathway associated with WPW, the types of activation, and their preferred treatments will help HCP in earlier referral for ablation as well as a safer initial treatment for WPW.
Meadows MC. Wolff-Parkinson-White Syndrome: Diagnosing and Treating Orthodromic vs. Antidromic Activation. Lynchburg Journal of Medical Science. 2023; 5(1).
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