Review Question - QID 217001

This patient with a history of myocardial infarction presents with palpitations and an electrocardiogram (ECG) showing irregularly irregular narrow complex tachycardia without clear P waves, which is consistent with diagnosis of atrial fibrillation. Given his history of coronary artery disease, the most appropriate next step in management is administration of a beta blocker, such as metoprolol, as it confers a mortality benefit.

Atrial fibrillation typically presents as palpitations and an irregularly irregular pulse. Diagnosis is typically made via ECG, which would show irregularly irregular QRS complexes without clear P waves. The causes of atrial fibrillation are numerous, including hypertension, structural heart disease, ischemia, thyroid disease, drug toxicity, or in settings of stress, such as sepsis. The most appropriate treatment for atrial fibrillation depends on a patient's comorbidities. It has been shown that beta blockers, such as metoprolol, are the preferred rate control medication for patients with history of myocardial infarction as they provide a mortality benefit. Beta blockers are also the preferred rate control method for patients with no specific contraindications to this medication - as in they are generally first-line treatment for most patients.

Van Gelder et al. review the rate control options in treatment of atrial fibrillation. They recommend that the choice of agent depends on the symptoms and clinical characteristics of the patient.

Figure/Illustration A is an ECG showing irregularly irregular QRS complexes (as denoted by the irregularity of the red triangles) and lack of clear P waves.

Incorrect Answers:
Answer 1: Adenosine can be used to slow conduction at the AV node long enough for diagnosis of specific types of supraventricular tachycardia (SVT). SVT is defined as any arrhythmia originating above and including the bundle of His, manifesting on ECG with narrow QRS complexes and rate greater than 100 beats per minute. This patient's ECG with irregularly irregular QRS complexes without clear P waves is consistent with atrial fibrillation, for which adenosine has no role in treatment.

Answer 2: Amiodarone is a potassium channel blocker antiarrhythmic agent that is sometimes used in the management of atrial fibrillation. However, it is not a first line medication and would not work towards rate control. Its side effects include hypothyroidism and pulmonary fibrosis among others.

Answer 3: Digoxin is a medication used for rate control and is helpful in patients with heart failure with reduced ejection fraction as it also increases heart contractility. However, this patient does not have heart failure and digoxin does not offer a mortality benefit to patients with coronary artery disease or history of myocardial infarction.

Answer 4: Diltiazem is a calcium channel blocker rate control agent that would be appropriate for this patient, but it does not confer the mortality benefit that a beta blocker would for patients with history of coronary artery disease. It would be better suited for patients who have relative contraindications to beta-blockade, such as those with asthma.

Bullet Summary:
Beta blockade is the preferred rate control method for atrial fibrillation in patients with coronary artery disease or history of myocardial infarction.