A 56-year-old man comes to the emergency department due to palpitations that started several hours ago. He has not had similar symptoms before. The patient has had no chest pain, shortness of breath, lightheadedness, or syncope. He drinks alcohol on weekends and does not use illicit drugs. He has no family history of heart disease. Blood pressure is 145/78 mm Hg. BMI is 40 kg/m². ECG is shown in the exhibit.

The patient is treated medically in the emergency department. He is then taken to the electrophysiology laboratory for radiofrequency catheter ablation to terminate his arrhythmia. The ablation procedure should create a conduction block through which of the following areas?

Question

A 56-year-old man comes to the emergency department due to palpitations that started several hours ago. He has not had similar symptoms before. The patient has had no chest pain, shortness of breath, lightheadedness, or syncope. He drinks alcohol on weekends and does not use illicit drugs. He has no family history of heart disease. Blood pressure is 145/78 mm Hg. BMI is 40 kg/m². ECG is shown in the exhibit.

The patient is treated medically in the emergency department. He is then taken to the electrophysiology laboratory for radiofrequency catheter ablation to terminate his arrhythmia. The ablation procedure should create a conduction block through which of the following areas?

Quizplus · Accepted Answer

11ec160b_3c87_d96d_9249_ef19da037f17_MD0001_00 This patient's ECG strip shows rapid and regular atrial activity in a saw-toothed pattern (flutter or F waves), consistent with atrial flutter. Narrow QRS complexes are typically present and the ventricular rhythm appears regular. Because the atrial rate is approximately 300/min, typical ventricular rates in atrial flutter are 150/min, 100/min, or 75/min due to 2:1, 3:1, or 4:1 conduction through the atrioventricular node, respectively. Atrial flutter shares many of the same triggers as atrial fibrillation; underlying comorbidities that cause atrial dilation (eg, heart failure) are often present and alcohol intake may contribute. Typical atrial flutter is caused by a large reentrant circuit that traverses the cavotricuspid isthmus, the region of right atrial tissue between the inferior vena cava and the tricuspid valve annulus. This region is identified during electrophysiologic study and is the target for radiofrequency ablation to interrupt the reentrant circuit and abolish atrial flutter. (Choice A) An accessory pathway that bypasses the atrioventricular node is present in atrioventricular reentrant tachycardia, also known as Wolff-Parkinson-White syndrome. ECG shows the triad of short PR interval, wide QRS complex, and slurred upstroke of the QRS complex (delta wave). (Choice C) The right ventricular outflow tract is the most common origination site of idiopathic ventricular tachycardia, a repetitive monomorphic ventricular tachycardia that occurs in the absence of structural heart disease. ECG shows a wide QRS complex with uniform QRS morphology and a regular rhythm. (Choice D) The pulmonary vein ostia are often the origination site of atrial fibrillation, and catheter ablation of pulmonary vein trigger sites (pulmonary vein isolation) may be used to treat symptomatic patients. ECG reveals an irregularly irregular rhythm with varying R-R intervals and absence of P waves. (Choice E) Dual electrical pathways (a slow and fast pathway) within or near the atrioventricular node are implicated in atrioventricular nodal reentrant tachycardia; the slow pathway is targeted for radiofrequency ablation. ECG shows narrow QRS complexes with a rapid rate and regular rhythm, and sometimes retrograde P waves. Educational objective: Atrial flutter demonstrates rapid and regular atrial activity in a saw-toothed pattern (flutter or F waves) on ECG. Typical atrial flutter is caused by a large reentrant circuit that traverses the cavotricuspid isthmus of the right atrium, which is the target site for radiofrequency ablation. __________ References: Electrophysiologic studies in atrial flutter. (http://www.ncbi.nlm.nih.gov/pubmed/1395202) Electrophysiological effects of catheter ablation of inferior vena cava-tricuspid annulus isthmus in common atrial flutter. (http://www.ncbi.nlm.nih.gov/pubmed/8548901)

A 56-Year-Old Man Comes to the Emergency Department Due to Palpitations