The delta wave represents the portion of ventricular muscle (left or right ventricle) that is activated before normal ventricular activation via the His-Purkinje system. Depending on the location of the accessory connection and the conduction of the AV node at a given time, the delta wave may be more or less apparent. The delta wave is manifest in the first portion of the QRS, and the vector may be positive (upright), negative (pseudo-Q wave), or isoelectric (inapparent), depending on the location of the accessory connection. The delta wave vector on the 12-lead ECG is frequently helpful in making a first approximation of the accessory connection location.
Is there a treatment of choice for patients with the Wolff-Parkinson-White syndrome who present in atrial fibrillation?
These patients will typically have an ECG with an irregularly irregular rhythm and a QRS that varies in width (depending on the ratio of AV node to accessory pathway penetration).
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In patients who are hemodynamically stable, AV nodal-blocking drugs (verapamil, adenosine, beta blockers, and digoxin) should not be used. These drugs can slow conduction through the AV node and paradoxically accelerate the ventricular response by increasing the conduction over the accessory connection. Furthermore, hypotension resulting from drug-induced vasodilation may result in increased catecholamine release which can directly enhance accessory connection conduction. It is in this setting that ventricular fibrillation is most likely to occur. Intravenous procainamide is the drug of choice, as it slows accessory pathway conduction and frequently converts the atrial fibrillation to normal sinus rhythm. In patients who are hemodynamically compromised, the use of direct current cardioversion is recommended.
How is PSVT with aberrancy distinguished from ventricular tachycardia?
In the hemodynamically stable patient with wide-complex tachycardia, always obtain a 12-lead ECG to help distinguish between different tachycardia mechanisms. Supraventricular tachycardias most frequently occur in young patients without any structural heart disease. Patients with aberrant conduction typically manifest either a right or left bundle branch block with the QRS characteristics typical for these conditions, and AV dissociation is never seen. Patients with ventricular tachycardia are usually older and have significant structural heart disease, such as prior myocardial infarction. The defining characteristic is the presence of AV dissociation, but other features which favor the diagnosis of ventricular tachycardia include QRS 0.14 second, right bundle branch block with a far left axis vector, and concordance of QRS vector in the precordial leads. If in doubt, assume the rhythm is ventricular tachycardia and treat accordingly.