A 47-year-old man with known coronary artery disease comes to the emergency department with chest tightness, sweating, and palpitations. His symptoms began abruptly 2 hours ago while he was at work. Six months ago, the patient underwent percutaneous angioplasty of the right coronary artery. Past medical history also includes anxiety and panic attacks. Blood pressure is 180/90 mm Hg and pulse is 110/min with a regular rhythm. An esmolol infusion produces rapid symptom relief and heart rate slowing. Which of the following portions of the ECG will be affected most significantly by the medication?

Question

A 47-year-old man with known coronary artery disease comes to the emergency department with chest tightness, sweating, and palpitations.  His symptoms began abruptly 2 hours ago while he was at work.  Six months ago, the patient underwent percutaneous angioplasty of the right coronary artery.  Past medical history also includes anxiety and panic attacks.  Blood pressure is 180/90 mm Hg and pulse is 110/min with a regular rhythm.  An esmolol infusion produces rapid symptom relief and heart rate slowing.  Which of the following portions of the ECG will be affected most significantly by the medication?

Quizplus · Accepted Answer

11ec160b_3b7d_2065_9249_537d10d11c00_MD0001_00 On an ECG, the P wave represents atrial depolarization and the QRS complex represents ventricular depolarization. The PR interval is the period from the beginning of atrial depolarization (start of P wave) to the beginning of ventricular depolarization (start of QRS complex). The longer the PR interval, the longer it takes for an electrical stimulus to travel from the SA node to the ventricles via the AV node, bundle of His, and fascicular branches. Drugs that slow AV nodal conduction, such as beta blockers, will prolong the PR interval. Beta blockers (except sotalol, which also has class III properties) do not have any specific effects on QRS or QT interval durations. (Choice A) The T wave represents ventricular repolarization. It is not affected by beta-adrenergic blockers. Myocardial ischemia can cause T wave inversion. (Choice C) The QRS complex represents ventricular depolarization. It is not affected by beta-adrenergic blockers. A widened QRS complex can occur in the setting of ventricular automaticity, left or right bundle branch blocks, or ventricular pacemakers. (Choice D) The ST-segment is a period of electrocardiographic inactivity that extends between ventricular depolarization and repolarization. It is not affected by beta-adrenergic blockers. ST-segment elevation or depression is usually a sign of myocardial ischemia. (Choice E) The QT interval represents the time needed for ventricular depolarization and repolarization (ventricular electrical systole). Long QT syndrome can be congenital or acquired. Antiarrhythmics such as quinidine and sotalol are most frequently associated with acquired long QT. However, most beta blockers have a minimal effect on the resting QT interval. Educational objective: Beta blockers decrease AV nodal conduction, leading to an increased AV nodal refractory period. This correlates to PR interval prolongation on an ECG.

A 47-Year-Old Man with Known Coronary Artery Disease Comes to the Emergency