George Ntaios

George Ntaios

A conversation with George Ntaios, MD, MSc (ESO Stroke Medicine), PhD, Assistant Professor of Internal Medicine, Department of Medicine, University of Thessaly

Interviewed by Stephen Makin, PhD, Clinical Lecturer at Glasgow University

They will be discussing the paper, “Real-World Setting Comparison of Nonvitamin-K Antagonist Oral Anticoagulants Versus Vitamin-K Antagonists for Stroke Prevention in Atrial Fibrillation: A Systematic Review and Meta-Analysis,” being published in the September 2017 issue of Stroke.

Dr. Makin: Thank you for taking the time to talk to us.

Prof. Ntaios: Thank you for the invitation to discuss our study.

Dr. Makin: Could I begin by asking you to summarize your study and its findings?

Prof. Ntaios: We aimed to summarize all available evidence from high-quality real-world observational studies about the efficacy and safety of non-vitamin-K-oral-anticoagulants (NOACs) compared to vitamin-K-antagonists (VKAs) in patients with atrial fibrillation (AF). Based on 28 identified studies, we found that dabigatran, rivaroxaban and apixaban, as compared to VKAs, are associated with lower risk of intracranial haemorrhage and similar risk of ischemic stroke and ischemic stroke or systemic embolism; apixaban and dabigatran with lower risk of mortality; apixaban with fewer gastrointestinal and major haemorrhages; dabigatran and rivaroxaban with higher risk of gastrointestinal haemorrhage; and dabigatran and rivaroxaban with a similar rate of myocardial infarction.

Dr. Makin: Given that we already have good RCT evidence for NOAC use, what does evaluating real-world studies add?

Prof. Ntaios: This is true, we do have good RCT evidence for NOAC use in AF patients. The conclusions from the real-world studies support the findings of the RCTs, do not uncover new safety concerns and strengthen their validity.

Dr. Makin: Has this review changed your practice?

Prof. Ntaios: No, as mentioned already, we already have good RCT evidence for NOAC use in AF patients, and the current meta-analysis points towards the same conclusions like the RCTs.

Dr. Makin: Are there any circumstances in which you prefer to use a VKA over NOAC?

Prof. Ntaios: NOACs should be avoided in patients with significant decline of renal function. In these patients, VKAs are the treatment of choice. Another subgroup of patients is patients with prosthetic valve where VKAs remain the treatment of choice.

Dr. Makin: As a geriatrician, I am concerned that older patients are often not included in RCTs, and many of my older patients prefer an NOAC, as they find it difficult to attend anticoagulation clinics. Did you find much data on the use of NOAC in older people?

Prof. Ntaios: Our study did not aim to answer this question. However, a previous publication has confirmed the value of NOACs in this patient group.

Dr. Makin: Do you feel that the question of NOAC versus VKA is settled now, or are there any further questions that need to be answered?

Prof. Ntaios: Yes, I think that there are strong data available that, in the AF population, the NOAC vs. VKA dilemma is now settled.

Dr. Makin: I noticed that the meta-analysis had a high I2 score, meaning high heterogeneity; did this surprise you?

Prof. Ntaios: No, heterogeneity is frequently identified in meta-analyses. This may be explained by several reasons, such as potential unmeasured residual confounding like selective prescribing, lack of information about patient characteristics, patient adherence and persistence to treatment, time-within-therapeutic-range for patients receiving VKA and physician adherence to prescribing indications.

Dr. Makin: Although NOACs seem to perform better than VKA antagonists, they are more expensive. Do you know of any information on the cost effectiveness of NOACs against VKAs? 

Prof. Ntaios: There are several cost-effectiveness studies of NOACs vs. VKAs in AF patients. In one recent study, Shah et al showed that all NOACs were more effective than adjusted dosed warfarin.