Why NICE recommends Heartflow FFR CT?
A good quality cardiac CT scan shows in fantastic detail the heart structures and specifically the coronary arteries.
Coronary artery disease remains the leading cause of premature death in the UK and can often strike unexpectedly in apparently well individuals. In those that have developed cardiac symptoms of chest discomfort or breathlessness, NICE have been recommending over the last 5 years that a Cardiac CT scan is the preferential method of evaluation.
Unfortunately, due to limitations in the availability of high-quality cardiac CT scanning, many specialists and hospitals have been unable to offer this service routinely with the long waits and poor access resulting in patients undergoing the more conventional exercise stress testing and invasive coronary angiography.
Reports have quoted up to an 8-fold shortfall between the number of cardiac CT scans required and those available (see link). During the Covid 19 pandemic these differences have been further exaggerated with the additional constraints of social distancing, increased scan time allocations to allow for equipment cleaning, and staff illness (link to Cardiology during Covid).
Despite these challenges, it is the extreme sensitivity that CT has for detecting significant coronary disease that has made it in the majority of cases, the preferential test for ruling out underlying coronary artery disease. Until recently this has in itself posed a problem, as cardiac CT detects even very small areas of plaque (cholesterol depositions) in the walls of the coronary vessels. because parts of the coronary artery affected by extensive plaque may become calcified over time, a cardiac CT alone may not be sufficient to differentiate between plaque that obstructs blood flow down the vessel, and plaque that does not. This is an important distinction since non-obstructive plaque is treated with medication and by addressing cardiovascular risk factors, whereas conversely obstructive plaque may require coronary angioplasty (stent deployment) or even coronary artery bypass graft surgery. Until recently, many patients have undergone a cardiac CT and, following the detection of extensive changes in the coronary arteries, have then had to undergo an invasive coronary angiogram – with the small risks of stroke, heart attack or vascular damage that this entails, to then not require any coronary stenting or bypass surgery.
To overcome this problem FFR CT developed by Heartflow Inc. utilises data collected at the time of the Cardiac CT scan which assesses not only the visual severity of the coronary narrowing but also whether the narrowing reduces flow down each of the main coronary vessels, that might require additional treatment.
Cardiologists have recognised for many years that a coronary artery narrowing usually starts limiting blood flow during exercise when it reduces the artery by about 70%, however this calculation is different for every coronary narrowing, in every artery, and in every patient. These variabilities are caused by numerous factors in the complex biological system that is the heart. These include the length of the narrowing, whether there exist sequential abnormalities, blood flow into the coronary artery itself and resistance downstream all play their part.
It is for this reason that hitherto it has often been necessary for patients with moderate coronary narrowing to undergo several tests including invasive coronary angiograms, stress nuclear SPECT studies, stress echocardiograms and invasive catheter-based assessments of coronary flow.
As a result of this and other data, NICE* and NHS England have been encouraging the uptake of Heartflow FFR CT by hospital Trusts although access does currently remain limited to centres with specific expertise. There is currently very limited access to Heartflow FFR CT in private medical practice but reassuringly most private medical insurers are beginning to understand the importance of this technique and agree to the reimburse the few specialist private cardiology facilities that offer the service. Heartflow FFR CT is a major step forward in delivering a high quality, convenient, one-stop, cost effective diagnosis for possible underlying life-threatening coronary artery disease and is likely to revolutionise the delivery of cardiology services over the next decade.
Dr Michael Hickman MD FRCP
Michael is a consultant cardiologist with 20 years of experience in the field of complex cardiovascular imaging. He has undertaken extensive research developing imaging techniques to assess blood flow parameters in heart muscle. In more recent years he has been clinical lead for cardiology at The Royal Surrey Foundation Trust and Clinical Cardiovascular Lead for Surrey Heartlands. He is passionate about improving health outcomes from Cardiovascular disease. Michael is a Founder Director of VCL.
NICE* aim for increased usage of Heartflow FFR CT