New guide addresses valvular heart disease

Managing patients with valvular heart conditions can be a real challenge. They often require lifelong monitoring, with replacement surgery and subsequent anticoagulation. Recently, in a joint effort, the American College of Cardiology (ACC) and the American Heart Association (AHA) revised their 1998 recommendations to create the ACC/ AHA 2006 Practice Guidelines for the Management of Patients with Valvular Heart Disease. The executive summary and recommendations were published in the Aug. 1, 2006, issues of the Journal of the American College of Cardiology and Circulation.

Besides revamping the best methods for evaluating, diagnosing, and choosing when patients are candidates for surgical intervention, the new practice guidelines address the best ways to manage anticoagulation-something that pharmacists can relate to.

According to the new guidelines, anticoagulation is indicated for the 30% to 40% of patients with mitral stenosis (MS) who develop atrial fibrillation. This is due to the fact that systemic embolization may occur in 10% to 20% of patients with MS, with an increasing risk related to age and coexisting atrial fibrillation. Treatment of an acute episode of rapid atrial fibrillation should consist of anticoagulation with heparin and control of ventricular response with either intravenous digoxin, calcium-channel blockers, or beta-blockers.

For women requiring long-term warfarin therapy who are attempting pregnancy, the new guidelines recommend performing frequent pregnancy tests with the substitution of unfractionated heparin (UFH) or LMWH for warfarin when pregnancy is achieved. Warfarin is considered relatively safe during the second and third trimesters of pregnancy but must be discontinued and switched to a heparin compound several weeks before delivery. UFH is generally considered safer than warfarin during pregnancy; however, monitoring can be an issue.

"UFH is difficult to monitor via the activated partial thromboplastin time (aPTT), and in some cases the aPTT may not be the best surrogate marker of efficacy/safety in the setting of pregnancy," said Groce, who is also a professor at Campbell University school of pharmacy.

All pregnant women with mechanical prosthetic valves must receive continuing therapeutic anticoagulation with frequent monitoring, according to the guidelines; which agent is best, however, is at best unclear. "The ACC/AHA guidelines remind us that there are insufficient grounds to make definitive recommendations about optimal/first-line therapy in pregnant patients with mechanical prosthetic heart valves," Groce explained, although there are certain advantages given to LMWHs over UFH in managing such patients, he added.

LMWHs cause less heparin-induced thrombocytopenia, have longer plasma half-life and a more predictable dose response than UFH, are administered more easily, lack laboratory monitoring, have the potential for once-daily administration, have a lower risk of osteoporosis, and appear to have a low risk of bleeding complications.

Following aortic valve replacement (AVR), warfarin is indicated to achieve an International Normalized Ratio (INR) of 2.0-3.0 or 2.5-3.5, depending on the type of valve used for the replacement. Warfarin is also recommended for mitral valve (MV) replacement to an INR of 2.5-3.5, but for those patients unable to take warfarin after MV replacement or AVR, aspirin is indicated in a dose of 75 mg to 325 mg per day. The addition of aspirin (75-100 mg once daily) to therapeutic warfarin is recommended for all patients with mechanical heart valves and for those patients with biological valves who have risk factors. Risk factors include atrial fibrillation, previous thromboembolism, left ventricular dysfunction, or a hypercoagulable condition.