Atrial fibrillation:   Slow(er), even if not steady, wins the race

AF is the most common arrhythmia, especially in the elderly. It is a major cause of stroke, but treatment can reduce that risk by two-thirds.^1-2

Important information for improving care of patients with AF

•  Rate control should generally be the first priority, with a target of <110 beats per minute; rhythm control is usually a secondary concern.³
• Even though AF markedly increases the risk of thrombotic stroke, anticoagulation is underused in these patients. The CHADS₂ prediction rule can guide this decision.⁴
• The HAS-BLED score system can help predict the risk of warfarin-induced bleeding.⁵ These principles apply to nearly all patients with AF, whether it is "paroxysmal" or "permanent."
• Dabigatran (Pradaxa) is a promising new alternative to warfarin, but its high cost, short half-life, and the limited knowledge about long-term side effects are concerns.^6-7 

Control the rate, or control the rhythm? Whatever the underlying cause, or if no reversible cause is found, AF requires careful management.

Rate control works at least as well as rhythm control, with fewer complications.

•  The AFFIRM trial studied 4,060 patients with AF who had a high risk of stroke or death and randomized them to regimens of rhythm vs. rate control.⁸
• The rate control strategy led to significantly fewer hospitalizations and adverse drug events, as well as a marginally lower risk of death.

Aim for a heart rate of under 110

• The Rate Control Efficacy in Permanent Atrial Fibrillation (RACE II) randomized patients to a lenient rate control strategy (resting heart rate < 110 ) or a strict one (resting rate < 80).
• Patients assigned to the lenient-control strategy had lower rates of the primary outcome, a composite of cardiovascular death, heart failure hospitalization, stroke, systemic embolism, bleeding, or life-threatening arrhythmias.¹⁰

An approach to rate control in AF

Target a resting heart rate of < 110 bpm using a beta-blocker, verapamil, or diltiazem. ⇒ Choice of agent will often be determined by other clinical conditionsIs further rate control needed? ⇒ YES ⇒ Consider combining agents, or add digoxin. ⇒ Is further rate control needed? ⇒YES ⇒ Consider amiodarone or specialist referral, especially in patients with lone AF, or ECG evidence of an underlying electrophysiological disorder, or when drug therapy has failed.

When rate control fails...

If rate control cannot be achieved, or if a patient’s symptoms cannot be managed with rate control alone, rhythm control is a logical next step, using antiarrhythmic drugs such as amiodarone, propafenone, or sotalol.

Anticoagulation decisions

The most dangerous result of AF is the development of clot in the fibrillating atria, which can break off and cause catastrophic embolic events. Most AF patients will require long-term anticoagulant or anti-platelet medication to reduce their risk of stroke.

Nearly all AF patients require antithrombotic medication

There is ample evidence that anticoagulation is vastly under-utilized in patients with AF, particularly the elderly. This appears to result from an incorrect assumption that the risks of bleeding from these regimens are greater than the risk of stroke, which is generally not the case.

Current guidelines suggest the following treatment strategies for most AF patients based on their CHADS₂ score. The HAS-BLED score can also be considered, especially for deciding between aspirin and an anticoagulant in patients with a CHADS₂ score of 1.⁵

What is the risk of stroke?

Use the “CHADS₂” score to determine the patient’s risk of stroke without anti-thrombotic therapy.⁴ Assign one point each for Congestive heart failure, Hypertension history, Age >75, Diabetes Mellitus, and 2 points for Stroke or TIA history.

Don’t overestimate the risks of anti-thrombotic therapy.

Use the “HAS-BLED” score to determine the patient’s risk of bleeding with warfarin⁵ 

INRs are often poorly controlled

Despite its impressive efficacy in preventing stroke in AF, warfarin is a difficult drug to use, for both prescribers and patients. It requires ongoing INR monitoring, and its effect can be influenced by drug interactions and diet changes (especially vitamin K-rich foods). Despite good efforts, many patients in typical care spend >40% of time outside therapeutic range of their INR,¹² exposing them to preventable risk of ischemic stroke (if INR is too low) or bleeding (if too high).

Then along came dabigatran

In late 2010, FDA approved dabigatran (Pradaxa), a new oral thrombin inhibitor. The RE-LY trial found it more effective than warfarin at reducing stroke risk, causing fewer intracranial hemorrhages but no significant difference in the risk of major bleeding overall. There was a non-significant advantage in the risk of death.⁷

A promising drug – with a few caveats

Dabigatran dosing based on creatinine clearance:

Other anticoagulants may soon be FDA approved for stroke prevention in AF. These include oral Factor Xa inhibitors such as rivaroxaban, apixaban, and edoxaban.

Cost

Many of the drugs used for rate or rhythm control and stroke prevention are available as affordable generics. Greater affordability can make a big difference in compliance.