![]() ![]() Occasionally, a pathway may conduct only in a retrograde fashion, in which case it is not being used when the patient is in normal sinus rhythm and there are no ECG changes at rest (this is called a concealed pathway). As long as the AV bypass tract conducts in the anterograde fashion, the bypass tract is called manifest, as it is often (but not always) seen on resting ECG when the patient is in normal sinus rhythm. Most AV bypass tracts are capable of conducting impulses both anterogradely (atria to the ventricles) and retrogradely (ventricles to the atria). What are the ECG findings of AV preexcitation? In this case, the QRS complex will be wide, as ventricular depolarization is taking place through muscle-to-muscle conduction rather than the His-Purkinje system. Occasionally (in 5 to 10% of patients with WPW), the impulses travel to the ventricles through the bypass tract and return to the atria via the AV node. This situation is called orthodromic AVRT. In most cases, the impulses travel down through AV node and up through the accessory pathway – this leads to a narrow-complex rhythm because the impulses are travelling rapidly as they normally would through the His-Purkinje system then return to the atria via the AV bypass tract. These circuits can be at the micro- or macro-level.ĪVRT is a type of macro re-entrant tachycardia, in which the impulses travel down one pathway and up through another. Reentrant rhythms – conduction of impulses through a self-sustaining circuit within the heart.Enhanced automaticity – depolarizations that either occur spontaneously in nonpacemaker cells (which wouldn’t normally depolarize spontaneously) or in pacemaker cells, but at a lower stimulation threshold than usual.Triggered activity – abnormal impulses that result from afterdepolarizations (fluctuations that occur in the membrane potential as the cell repolarizes).Recall that there are three mechanisms for the development of cardiac dysrhythmias: The most common tachydysrhythmia seen in WPW is atrioventricular re-entrant tachycardia (AVRT) – this is seen in 80% of patients with WPW and is what paramedics would most commonly be called for. WPW is a type of preexcitation syndrome in which there are ECG findings of an atrial-ventricular bypass tract (often, but erroneously, called Kent bundles) and the patient demonstrates related tachydysrhythmias. Preexcitation describes the situation in which impulses from the SA node or atrium reach the ventricle through an accessory pathway (a bypass tract) in addition to the AV node. Review the management of SVT in WPW and consider potential complications.Review the physiology of Wolff-Parkinson-White Syndrome (WPW).By opening this dialogue, we hope that these new perspectives will be translated into practice to create a smoother, more efficient, and overall positive transition for patients as they pass through the ED doors. The series offers in-hospital providers a glimpse into the challenges and scope of practice of out-of-hospital care while providing pre-hospital providers with an opportunity to learn about the diagnostic pathways and ED management of common (or not-so-common) clinical presentations. Sirens to Scrubs was created with the goal of helping to bridge the disconnect between pre-hospital and in-hospital care of emergency patients. As you begin to coach her through vagal maneuvers and reach for your adenosine she advises you ‘I have something called Wolff-Parkinson-White – does that change anything?’ You think maybe it does, but you’re not sure. On arrival, you find her clinically stable in a narrow-complex, regular tachycardia at a rate of 180bpm. You are dispatched to Jasmine, a 31yo patient, for palpitations. ![]()
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