16 October 2019

An affair of the heart where you don’t want to miss a beat

It is estimated that in England alone, some 425,000 people have unsuspected atrial fibrillation.

Atrial fibrillation (AF) describes chaotic electrical activity in the upper chambers of the heart – the atria – that results in an erratic heart rhythm. It becomes ever more prevalent with age; around one in seven over-85s have the condition. AF can make patients feel breathless or light-headed, but for many people it causes no symptoms. It is estimated that in England alone, some 425,000 people have unsuspected AF. This matters because blood can coagulate inside the fibrillating atria. If a piece of clot breaks off, it typically lodges in an artery to the brain, causing a stroke. Around one in five strokes are AF-related.

Thinning AF patients’ blood with anticoagulant drugs cuts this stroke risk by two-thirds. If we could detect the thousands of people with undiagnosed AF and treat them, we should be able to prevent an awful lot of disability and death. AF ought, by rights, to be easy to pick up. Lay a hand on someone’s wrist, feel an irregular pulse, arrange an ECG to confirm the diagnosis: job done.

The UK National Screening Committee (NSC), looked at whether to screen for AF in 2014, and concluded there was insufficient evidence to support a national programme. In part this was because warfarin, the only oral anticoagulant available for many decades, is a problematic drug. It frequently causes wild swings in blood thinning – increasing the risk of the biggest problem with anticoagulation, major haemorrhage – and requires frequent blood tests and dose changes to keep its effects controlled. Doctors have traditionally been wary of using warfarin in frail elderly patients at risk of falls – the very population with the highest prevalence of AF.

The landscape has changed dramatically over the past few years with the advent of a new class of oral anticoagulants, NOACs. Although major haemorrhage remains the feared side-effect, NOACs produce consistent blood thinning with no need for monitoring or dose adjustment to keep them safe. Where warfarin used to be thought suitable for only a minority of AF patients, the majority are now being treated with NOACs.

In light of this, the NSC re-examined the screening question in August, but again stopped short of recommending a national programme. The risk of stroke with AF varies depending on the presence of other factors such as diabetes and high blood pressure. It is entirely possible that people with unsuspected AF may have very different characteristics to those who present to doctors and get diagnosed. If that is the case, identifying and anticoagulating them may do more harm than good.

It is also unclear at what age any screening should start: pitch it too young and the cost-benefits could get lost, drowned out by high numbers of false positives (people with an irregular pulse for benign reasons). There is also uncertainty as to whether different subtypes of AF carry the same stroke risk.

Cambridge University is currently leading a multi-centre trial called Safer, which will help to address these uncertainties. The NSC plans to revisit AF screening once its results are published in five years’ time. But this measured approach has not gone down well with everyone. Lobby groups, part-funded by drug companies marketing NOACs, have been encouraging patients to press the NSC for an immediate screening programme. Some doctors are launching “case-finding” initiatives, much to the dismay of colleagues who believe in getting clear evidence before changing practice.

This already contested arena is set to become even more complex thanks to wearable technology. Both Apple Watch and FitBit now claim to be able to detect AF. With false positive rates as high as 95 per cent for people in their fifties, the NHS is braced for a surge in worried-well device-wearers. Even the few who ultimately prove to have AF are likely to be at low risk. The thought of the work involved in sorting all this out makes my heart skip more than a few beats.