This briefing describes the regulated use of the technology for the indication specified, in the setting described, and with any other specific equipment referred to. It is the responsibility of healthcare professionals to check the regulatory status of any intended use of the technology in other indications and settings.
Two PressureWire fractional flow reserve (FFR) devices (St Jude Medical) are currently available: PressureWire Aeris and PressureWire Certus (with Agile Tip). Both are class III medical devices and received CE marking in 2009 and 2012 respectively.
The PressureWire FFR devices measure FFR, a physiological parameter used to assess the severity of stenoses in the coronary arteries. This briefing describes the use of PressureWire FFR devices in the investigation of stenoses in coronary arteries. In this context they are designed to determine whether a stenosis detected during angiography is functionally significant (that is, causes ischaemia). FFR can potentially inform the decision about whether to perform revascularisation, and on which lesions, or manage the symptoms conservatively with medical therapy.
The PressureWire FFR devices may also be used in assessing blood flow after stent placement and in investigating renal arteries. These uses are within the intended use of the device and covered by the CE mark, but are outside the scope of this briefing.
The PressureWire FFR devices are used by interventional cardiologists in a cardiac catheterisation laboratory setting, during diagnostic angiography or percutaneous coronary interventions (PCI).
Angiography is an X-ray based imaging technique that uses a contrast agent to visualise narrowing (stenosis) in the coronary arteries that may be responsible for cardiac ischaemia. Angiography uses a percutaneous catheter introduced to the coronary arteries via a peripheral artery (femoral or radial), and guided by a guidewire.
PCI involves treating coronary artery narrowing by balloon angioplasty, with or without the use of a stent, under angiography. Coronary artery bypass grafting (CABG) may be necessary in severe cases.
The PressureWire Certus (with Agile tip) and Aeris devices are guidewires with a diameter of 0.014 inch and a sensor element at the tip. The Certus device is used with the Quantien proprietary monitor unit (St Jude Medical), purchased separately, whereas the Aeris uses wireless transmission to a receiver unit connected to monitoring platforms with FFR capability.
During PCI, the PressureWire FFR device and catheter are moved through the arterial system. The PressureWire FFR device can then be directed until the sensor tip is distal to the lesion of interest, recording arterial pressures both proximal and distal to the stenosis, enabling the FFR to be calculated.
The measurement takes place under artificially induced conditions of maximal blood flow (hyperaemia). This is usually achieved by injection of a drug such as adenosine. Under these conditions coronary blood pressure is proportional to blood flow, and the ratio of pressure before and after the stenosis is equivalent to the ratio of flow. FFR is defined as the distal coronary artery pressure divided by the proximal coronary artery pressure.
Lesions with an FFR of 0.80 or less are indicated for revascularisation in several guidelines (Montalescot et al. 2013; Patel et al. 2012; Wijns et al. 2010). There is significant inter-operator variability in the visual assessment of coronary stenoses (Carrick et al. 2011; Hoole et al. 2011), but very severe or very mild stenoses are less uncertain. FFR measurement is typically used in determining the functional significance of intermediate lesions (for example, 40–70% stenosis).
Diagnostic angiography is currently the standard method used in the NHS if invasive investigation is needed to assess the severity of coronary artery disease. Angiography uses a catheter. A guidewire with FFR capability may be introduced subsequently into the catheter, or may be used for both the conventional guidewire function and pressure measurement.
NICE is aware of the following CE marked device that appears to fulfil a similar function:
FloWire Doppler guidewire (Volcano Corporation)
Alternative investigations to determine whether to perform revascularisation include non-invasive testing, such as exercise tolerance testing, dobutamine stress echocardiography, myocardial perfusion imaging using radionuclides and magnetic resonance perfusion imaging. Intravascular ultrasound allows the true dimensions of the lesion and the composition of the vessel wall to be visualised (Dawkins et al. 2005).
Data from the British Cardiovascular Intervention Society indicate that in 2012, 13,762 FFR procedures were carried out compared with 6407 intravascular ultrasound procedures (during both diagnostic angiography and PCI; Ludman 2013a).
Each PressureWire FFR device is single use. A Quantien monitor (St Jude Medical) is also needed to use the PressureWire Certus (with Agile tip). The PressureWire Aeris device can also be used with a Quantien monitor (which includes the wireless receiver unit), or the receiver unit can be bought separately to allow the use of another monitoring platform with FFR capability. The monitors and receiver units can be used more than once.
The list prices of the PressureWire FFR devices, excluding VAT, are:
PressureWire Aeris – £598.80
Aeris receiver unit – £399 (only necessary if the Quantien monitor is not purchased)
PressureWire Certus (with Agile tip) – £499
Quantien monitor – £22,500
1 year full service contract – £1000
2 year service contract – £1499.99.
Cables to connect to the catheterisation laboratory monitors are likely to cost from £100 to £300 each depending on the system used.
Maximal hyperaemia is needed to correctly measure FFR. This is most often achieved by giving adenosine intravenously or by intracoronary bolus. The measurement of FFR takes an extra 5–20 minutes during the angiography and there is a significant degree of technical skill and knowledge needed to ensure that pressure measurements from both the PressureWire FFR device and catheter are accurate. However, these should be within the standard competencies of an experienced interventional cardiologist.
FFR is used for diagnostic testing and to guide treatment decisions.
The NICE clinical guideline on stable angina (NICE clinical guideline 126) states that patients should normally be treated medically. However, for people whose symptoms are not satisfactorily controlled with optimal medical treatment, coronary angiography to guide treatment strategy should be considered. Treatments may include revascularisation by PCI or coronary artery bypass surgery (CABG). The guideline states 'Additional non-invasive or invasive functional testing may be required to evaluate angiographic findings and guide treatment decisions'.
A 2011 study abstract reported that, in a UK regional cardiology centre, the indication for FFR measurement in people with NSTEMI was an 'intermediate coronary lesion (that is, 40– 80% stenosis severity) associated with diagnostic and treatment uncertainty' (Carrick et al. 2013).
The European Society of Cardiology guideline on the management of stable coronary artery disease indicates that 'FFR is recommended to identify hemodynamically relevant coronary lesion(s) when evidence of ischaemia is not available' and 'revascularization of stenoses with FFR <0.80 is recommended in patients with angina symptoms or a positive stress test' (Montalescot et al. 2013).
The American College of Cardiology issued guidelines in 2012 indicating the different situations in which using FFR for assessing lesion severity was appropriate, and the level of certainty. It also indicated that 'in patients without previous non-invasive imaging, or patients in whom the prior testing is not in concordance with the symptoms or angiographic findings......for lesions between 50% to 69%, invasive FFR is the test preferred for diagnostic purposes' (Patel et al. 2012; Patel 2013).
Measurement of FFR is already part of the pathway in some centres for people referred for PCI, when there is uncertainty about the significance of stenosis from non-invasive imaging. It is estimated that 10–18% of people referred for PCI currently have FFR measured. There is agreement that it could be used more widely, including in different settings such as diagnostic-only cardiac catheterisation laboratories in addition to those capable of performing PCI, and as a decision tool for people referred for CABG, for whom PCI may be suitable.
Barriers for wider use are the cost per use, additional time per procedure, a perceived or actual lack of expertise, and whether cardiac catheterisation laboratories can be organised to perform FFR measurement.