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Supraventricular Tachycardia

Terms in this set (131)

1.) Only SVT with potential for sudden cardiac death in a subset of patients
2.) In the normal heart, the conduction of an atrial arrhythmia to the ventricle is determined by the refractory periods of the AV node and His-Purkinje system
- If the rate of the atrial arrhythmia exceeds the conduction properties of the AV node, some of the atrial
impulses will be blocked from conduction to the ventricles. 3.) If an accessory pathway with rapid conduction velocity and a short refractory period is present, each beat of a rapid atrial arrhythmia may be conducted to the ventricle. 4.) Rapid accessory pathway conduction of atrial fibrillation may lead to ventricular fibrillation, hemodynamic decompensation, and death
5.) Although uncommon, ventricular fibrillation or cardiac arrest may be the first presentation of WPW, particularly in older children
- The rapidity of anterograde conduction in the accessory pathway is measured by the shortest preexcited R-R interval, with an interval of less than 220-250 ms conferring increased risk
6.) Children with WPW are also at increased risk of developing atrial fibrillation, with a risk of 12 % in a large prospective study
- ECG during preexcited atrial fibrillation demonstrates a baseline of fine and irregular atrial activity, an irregularly irregular wide complex tachycardia, and occasional narrow QRS complexes from normally conducted impulses
7.) Other risk factors for sudden cardiac death are age less than 30 years, male gender, history of atrial fibrillation, syncope, congenital or other heart disease, and familial WPW
1.) Pathways conduct slowly and decrementally and typically only exhibit anterograde conduction
2.) Mahaim fibers have also been described as an AV node-like structure
3.) Unlike WPW, the slow conduction properties of Mahaim fibers result in minimal or no preexcitation during sinus rhythm
4.) Preexcitation can be intermittent and manifests as a left bundle branch block pattern with a normal P-R interval
5.) Patients who do not demonstrate preexcitation may have a deficiency of normal septal Q waves in the lateral leads, which can be a subtle clue for the presence of a Mahaim fiber
6.) The most common type of tachycardia associated with Mahaim fibers is an antidromic reentrant tachycardia with anterograde conduction in the Mahaim fiber and retrograde conduction through the AV node
7.) Since the right ventricle is depolarized first in tachycardia: a wide complex tachycardia with a left bundle branch block pattern
8.) Retrograde P waves are difficult to visualize in this tachycardia as they usually fall in the terminal portion of the QRS
9.) Other forms of tachycardia are possible in the presence of a Mahaim fiber but are less common:
- AV nodal reentrant tachycardia is found in up to 10 % of patients with a Mahaim fiber, such that the Mahaim fiber is a bystander pathway that is not a part of the tachycardia circuit but will conduct the impulses in an anterograde fashion to give a wide complex tachycardia
- Rarely, Mahaim fibers can produce tachycardia via spontaneous automaticity originating from the fiber. Unlike WPW, the slow conduction of Mahaim fibers does not allow for rapid conduction of atrial tachycardia.