Pattern of anticoagulation control after heart valve surgery at the Kenyatta National Hospital, Nairobi.

OBJECTIVE To determine the pattern of anticoagulation control for post heart-valve surgery for patients on follow up at Kenyatta National Hospital (KNH). DESIGN A combined prospective and restrospective hospital-based study. Retrospective period from January 1991 to 31st August 1997, while the prospective period was from 1st September 1997 to 31st November 1999. SETTING Cardiothoracic surgery clinic, Kenyatta National Hospital, Nairobi. PATIENTS Post heart valve surgery patients on warfarin and attending the cardiothoracic surgery clinic at Kenyatta National Hospital. MAIN OUTCOME MEASURES Clinic attendance intervals, average warfarin dosages, interval of dosage change, INR values and variations from accepted normal. RESULTS A total of 103 patients fulfilled the criteria for inclusion into the study consisting of 77 mitral valve replacements, 18 aortic valve replacements, seven double valve replacements and one mitral valve repair. The total follow up time for the study period is 316.9 patients years. On average, patients attended their anticoagulation clinic once every 59 days. The average dose of warfarin prescribed was 6.81 mg daily (+/-2.67 mg), with double valve replacement patients receiving a statistically significant lower dosage of 6.04 mg (+/-1.36 mg), (95% confidence limits). On average, a warfarin dose change was made 1.48 times a year per patient. For all the patients, the mean INR was 2.50 (+/-1.18). The respective values for mitral, aortic, double valve replacement and the mitral repairs were 2.53 (+/-1.21), 2.32 (+/-1.04), 2.5 (+/-1.05) and 2.02 (+/-0.53), respectively. Mitral valve repair patients maintained a significantly lower level of INR (95% confidence limits). Only during 18% of the follow up time was adequate anticoagulation maintained. During the study period only 6.9% of patients were able to maintain adequate anticoagulation for 50% or more of their follow up time. CONCLUSION Anticoagulation control at the KNH still needs some improvements in clinic attendance and better dosage adjustments to achieve more appropriate INR values.