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Chapter 79: Mechanisms of Cardiac Arrhythmias and Conduction Disturbances

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A 45-year-old woman presents to the emergency department after experiencing frequent and intermittent regular palpitations over the last several days. Her presenting electrocardiogram reveals ventricular bigeminy, and monitoring demonstrates rapid runs of ventricular tachycardia of the same morphology as her premature ventricular contractions (PVCs). The consultant cardiologist diagnoses her with right ventricular outflow tract ventricular tachycardia. Which of the following tachycardias shares the same arrhythmia mechanism?

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A. Bundle branch reentry tachycardia

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B. AV reentry using an accessory bypass tract

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C. Atrial flutter

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D. Atrial tachycardia

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E. AV nodal reentry tachycardia

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The answer is D. (Hurst’s The Heart, 14th Edition, chap. 79). The arrhythmic mechanism of right ventricular outflow tract ventricular tachycardia is enhanced or abnormal impulse formation (either triggered or automatic activity). Atrial tachycardia occurs as a result of enhanced pacemaker activity of ectopic sites within the atria. The arrhythmic mechanism of atrial tachycardia is either enhanced or abnormal impulse formation (from enhanced automaticity or triggered activity) as well as reentry. Bundle branch reentry tachycardia (option A), AV reentry using an accessory bypass tract (WPW or concealed accessory AV connection) (option B), atrial flutter (option C), and AV nodal reentry tachycardia (option E) are all reentrant tachycardias.

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A 79-year-old man is admitted overnight to the coronary care unit for symptomatic severe sinus bradycardia. You have held his beta-blocker and have tentatively scheduled the implantation of a permanent dual-chamber pacemaker for the following day. Due to his persistent heart rate of 35 bpm associated with weakness, you decide to start isoproterenol. Which of the following regarding the If current is incorrect?

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A. The If current is referred to as a “funny” current because, unlike most voltage-sensitive currents, it is activated by hyperpolarization

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B. The If is a mixed Na-K inward current modulated by the autonomic nervous system through cyclic adenosine monophosphate

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C. If is responsible for heart rate control by the autonomic nervous system

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D. The contributions of the If and the potassium channel (IK) are equal in the SA node, AV node, and Purkinje fibers

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E. The depolarization of If activates L-type Ca (ICa,L) current, which provides Ca to activate the type 2 cardiac ryanodine receptor (RyR2)

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The answer is D. (Hurst’s The Heart, 14th Edition, chap. 79). The contributions of the If and the potassium channel ...

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