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Figure A
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Figure B
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Figure C
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Figure D
Figure E
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This patient presents with atrioventricular reciprocating tachycardia (AVRT), as demonstrated by her EKG in Figure F. Patients with Wolff-Parkinson-White (WPW) syndrome (Figure E) are predisposed to developing AVRT. Given this patients history of having similar spells and a previous diagnosis of a conduction abnormality the history points toward underlying WPW rather than SVT despite SVT being the most common cause of symptoms as described in the clinical scenario. WPW syndrome is caused by the presence of an accessory electrical bypass tract between the atria and the ventricles (Illustration A). Electrical signals traveling down this pathway may stimulate the ventricles to contract prematurely, resulting in AVRT (Illustration B). Three common features of AVRT on EKG are (1) Rate between 200-300 bpm, (2) Hidden P wave buried in the QRS complex, (3) Narrow QRS. When patients are taken out of AVRT via vagal maneuvers, adenosine, or cardioversion, the patient's baseline WPW will be observed on EKG. WPW on EKG is characterized by (1) Shortened PR interval (<120ms) and (2) Delta wave (slurring slow rise of initial portion of QRS). The definitive treatment of WPW is a destruction of the abnormal electrical pathway by radiofrequency catheter ablation. Figures A-D are described in the incorrect answer choices below. Figure F demonstrates the characteristic pattern of AVRT. Illustration A is a schematic demonstrating the bypass tract and corresponding EKG findings in WPW. Illustration B is a schematic demonstrating AVRT as compared to AVNRT, another common supraventricular tachycardia. Incorrect Answers: Answer 1: Figure A demonstrates atrial fibrillation. Since this patient is no longer tachycardic, she cannot be in atrial fibrillation, and it is not her underlying rhythm. Answer 2: Figure B demonstrates normal sinus rhythm. This patient is more likely to have WPW at baseline causing her AVRT. Answer 3: Figure C demonstrates 2nd degree (Mobitz type 1) AV block. This is not known to cause AVRT and thus would be unlikely to be this patient's underlying rhythm. Answer 4: Figure D demonstrates complete (3rd degree) AV block. This is not known to cause AVRT and thus would be unlikely to be this patient's underlying rhythm.
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