Atrial Fibrilation

A 78-year-old man is evaluated in the emergency department for a 1-week history of palpitations and weakness. He has had multiple similar episodes in the past year but has never sought treatment. His other medical problems include hypertension and type 2 diabetes mellitus, and his medications are lisinopril, hydrochlorothiazide, and metformin. He has no history of heart disease and had a normal electrocardiographic exercise stress test 1 year ago.

On physical examination, he is alert and in no acute distress. Blood pressure is 135/80 mm Hg, heart rate is 143/min and irregular, respiration rate is 14/min, and oxygen saturation is 98% with the patient breathing room air. On cardiac examination, there are no murmurs. Lungs are clear.

Electrocardiogram shows atrial fibrillation with a rapid ventricular rate without evidence of ischemic changes. Cardiac enzyme values are normal. His heart rate decreases to 74/min with administration of labetalol.

Which of the following is the most appropriate long-term treatment for this patient?

	A Atrioventricular nodal ablation and pacemaker implantation
	B Metoprolol and aspirin
	C Metoprolol and warfarin
	D Procainamide

Key Points

• Strategies of rate versus rhythm control for atrial fibrillation are similar with respect to symptoms, mortality, and stroke risk.
• Most patients with atrial fibrillation are treated with a combination of rate control and long-term anticoagulation.

Answer and Critique (Correct Answer = C)

This patient is best treated with rate control and anticoagulation. Atrial fibrillation is the most common clinically significant arrhythmia and accounts for the most hospitalizations for cardiac arrhythmias. It occurs in less than 1% of patients ages 60 to 65 years but in 8% to 10% of patients older than 80 years. The estimated risk for stroke in affected patients is 5% per year without anticoagulation. In patients with nonvalvular atrial fibrillation, warfarin with a target INR of 2.0 to 3.0 has been shown to decrease stroke risk by an average of 62%, compared with a 19% decrease with aspirin therapy. To determine whether the risk of stroke is high enough to warrant chronic anticoagulation, risk stratification scores have been developed. One such stratification scheme is known as CHADS₂ score: Congestive heart failure, Hypertension, Age >75 years, Diabetes, Stroke or transient ischemic attack (TIA). Patients are given 2 points for a history of stroke or TIA (the strongest risk factor) and 1 point for all other risk factors. This patient has a CHADS₂ score of 3. The risk of stroke is lowest in patients with a CHADS₂ score of 0 (1.2%). The risk is 18% for a CHADS₂ score of 6 (maximum score). Patients with a CHADS₂ score of ≥3 and patients with a history of stroke are at high risk and should be considered for chronic anticoagulation with warfarin. Patients with a CHADS₂ score of 1 or 2 should be assessed on an individual basis for aspirin versus warfarin therapy.

In patients who tolerate atrial fibrillation with few symptoms, restoration of normal sinus rhythm is not indicated. Strategies of rate versus rhythm control have been found to be similar with respect to symptoms, mortality, and stroke risk. More hospitalizations and adverse drug reactions occur in patients receiving rhythm control compared with rate control. This elderly patient would be at significant risk of drug side effects from anti-arrhythmic agents and would likely have breakthrough episodes of atrial fibrillation. Therefore, in addition to chronic anticoagulation with warfarin, this patient should receive medication to control the ventricular rate, such as a β-blocker.

Atrioventricular nodal ablation for atrial fibrillation with pacemaker placement should be reserved for those patients who do not tolerate pharmacologic therapy. New ablation strategies are being investigated and are increasingly recommended in clinical practice guidelines. These include catheter-directed ablation of the pulmonary vein ostia within the left atrium. The success rate of this procedure is as high as 88% at 6 months without requiring pacemaker placement.

Bibliography

1. Snow V, Weiss KB, LeFevre M, McNamara R, Bass E, Green LA, Michl K, Owens DK, Susman J, Allen DI, Mottur-Pilson C; AAFP Panel on Atrial Fibrillation; ACP Panel on Atrial Fibrillation. Management of newly detected atrial fibrillation: a clinical practice guideline from the American Academy of Family Physicians and the American College of Physicians. Ann Intern Med. 2003;139:1009-17. [PMID: 14678921]
2. Gage BF, Waterman AD, Shannon W, Boechler M, Rich MW, Radford MJ. Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation. JAMA. 2001;285:2864-70. [PMID: 11401607]

Acute Coronary Syndrome

A 49-year-old man is evaluated in the emergency department for chest discomfort accompanied by nausea and dyspnea that began 2 hours ago. On physical examination, blood pressure is 109/78 mm Hg and heart rate is 88/min. There is no jugular venous distention and no carotid bruits. The lungs are clear. Cardiac examination shows a normal S1 and S2 and no gallops, rubs, or murmurs. The troponin level is 6 ng/mL (normal <0.5 ng/mL). Electrocardiogram shows a 1-mV ST elevation in leads II, III, and aVF.

He is treated with enoxaparin, aspirin, metoprolol, and glycoprotein receptor blockers and is taken to the cardiac catheterization laboratory. A stent is placed in a subtotally occluded right coronary artery. A follow-up echocardiogram shows normal wall motion, normal valve function, and a normal ejection fraction. By day 4, he has no complications and is prepared to be discharged.

In addition to aspirin, clopidogrel, and metoprolol, which of the following medications should be given at discharge?
A Atorvastatin
B Gemfibrozil
C Niacin
D Warfarin

Key Point
In patients with an acute coronary syndrome, statin therapy is indicated regardless of the serum cholesterol level.

Answer and Critique (Correct Answer = A)

This patient has survived a small inferior wall myocardial infarction and was successfully treated with a stent. At discharge, he should receive aspirin, metoprolol, clopidogrel for at least 180 days, and a statin regardless of his serum cholesterol level. In patients with coronary artery disease, especially those presenting with symptoms and those undergoing revascularization by either stenting or bypass graft surgery, statin therapy reduces late cardiovascular events despite having minimal or no effect on the angiographic appearance of the coronary arteries.

The PROVE IT-TIMI 22 study compared a moderate-dose statin (pravastatin, 40 mg/d) with a high-dose statin (atorvastatin, 80 mg/d) in patients hospitalized for acute coronary syndrome. The median LDL cholesterol levels achieved were 95 mg/dL by the pravastatin group and 62 mg/dL for the atorvastatin group. Those receiving atorvastatin had a 16% reduction in the composite endpoint of death from any cause, myocardial infarction, unstable angina requiring rehospitalization, coronary artery revascularization, and stroke during 2 years of follow-up. These results showed evidence of benefit from early aggressive LDL cholesterol lowering with high-dose atorvastatin.

Warfarin is not indicated after ST-elevation myocardial infarction treated by stenting unless there is another indication such as atrial fibrillation, deep venous thrombosis, or intracardiac thrombus.

Niacin for hypertriglyceridemia may be needed, but at this time the triglyceride values are not reported and may be falsely elevated early in the course of ST-elevation myocardial infarction. The first line of treatment would be statins even for normal LDL cholesterol levels in patients with documented coronary artery disease. The combination of statins with a fibrate (e.g., gemfibrozil) is attractive for patients who have both high cholesterol and triglyceride levels or for those who continue to have elevated triglyceride levels after reaching their LDL cholesterol target on statin therapy. However, in this patient, the best initial choice is a statin.
Bibliography

1. Ray KK, Cannon CP, Ganz P. Beyond lipid lowering: What have we learned about the benefits of statins from the acute coronary syndromes trials? Am J Cardiol. 2006;98:18P-25P. Epub 2006 Sep 29. [PMID: 17126675]