A 56-year-old woman comes to the clinic due to a sensation she has had for 3 weeks that her heart is skipping beats. The patient has had no chest pain, dyspnea, or diaphoresis. Medical history includes hypertension and well-controlled type 2 diabetes mellitus. Blood pressure is 155/90 mm Hg. Cardiopulmonary examination shows an irregular heart rate. The ECG is shown in the exhibit. Which of the following is the most likely diagnosis?

Question

A 56-year-old woman comes to the clinic due to a sensation she has had for 3 weeks that her heart is skipping beats.  The patient has had no chest pain, dyspnea, or diaphoresis.  Medical history includes hypertension and well-controlled type 2 diabetes mellitus.  Blood pressure is 155/90 mm Hg.  Cardiopulmonary examination shows an irregular heart rate.  The ECG is shown in the exhibit.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec25c8_d34e_8d49_bc81_33f3f844bcf6_MD0003_00 This patient's ECG findings (best seen in lead V5) show Mobitz type I second-degree (Wenckebach) atrioventricular (AV) block, which is recognized by progressive prolongation of the PR interval followed by a dropped QRS complex. The distance between the start of each P wave is constant (constant P-P interval); therefore, as the PR interval prolongs the R-R interval progressively decreases. ECG often demonstrates group beating, which is repetitive grouping of QRS complexes (eg, drop occurs after every 3 QRS complexes). ECG The block usually is located within the AV node, and causes include elevated vagal tone (eg, highly trained athletes), excessive pharmacologic AV nodal blockade (eg, beta blockers), ischemia, and age-related degeneration of the conduction system. Patients usually are asymptomatic, and management involves only observation and correction of potential reversible causes (eg, reduction of pharmacologic AV nodal blockade). In contrast, Mobitz type II second-degree AV block usually involves a block in the His-Purkinje system below the AV node. It is recognized on ECG by a constant PR interval with randomly dropped QRS complexes (Choice E). Patients can be asymptomatic or symptomatic (eg, fatigue, lightheadedness, syncope). Regardless of whether symptoms are present, the arrhythmia can progress to complete AV block and placement of a permanent pacemaker usually is necessary. ECG (Choice A) In atrial fibrillation, there is no organized atrial activity, and impulses are conducted in a random and unpredictable manner. This leads to an absence of discernible P waves and an irregularly irregular rhythm with varying R-R intervals. atrial fibrillation (Choice B) Complete (third-degree) AV block involves complete failure of impulse conduction from the atria to the ventricles. On ECG, P waves are entirely unrelated to QRS complexes and can be found before, after, or even buried in the QRS complexes. Complete (third-degree) AV block (Choice C) First-degree AV block is due to delayed impulse transmission from the atria to the ventricles, leading to a prolonged PR interval (>0.20 sec). The PR interval remains constant, and a QRS complex follows every P wave. First-degree AV block Educational objective: Mobitz type I atrioventricular (AV) block is recognized by progressive prolongation of the PR interval followed by a dropped QRS complex. The block typically is located within the AV node. In contrast, Mobitz type II AV block usually is located in the His-Purkinje system. Patients with Mobitz type I AV block usually are asymptomatic, and management involves observation and correction of reversible causes. References: Electrocardiographic manifestations: diagnosis of atrioventricular block in the emergency department. (http://www.ncbi.nlm.nih.gov/pubmed/14751485)

A 56-Year-Old Woman Comes to the Clinic Due to a Sensation