Does Routine Pressure Wire Assessment Influence Management Strategy at Coronary Angiography for Diagnosis of Chest Pain?

The choice of management in an individual patient is determined largely by the presence and distribution of significant coronary narrowings. Usually, this significance is judged by the visual estimation of a narrowing on an angiogram. However, although this is the standard way of assessing coronary narrowings, it is now widely published that pressure wire measurements are more accurate because they assess the true physiological consequences of the narrowing. Interventional cardiologists now frequently use Fractional Flow Reserve (FFR) measurements to help them decide if arteries require stenting.The hypothesis for this study is that routine measurement of FFR in the main coronary arteries could provide diagnostic information above and beyond that obtained by an angiogram alone. This additional information may well then affect the choice of management in a proportion of these patients. For example, a narrowing considered to be significant angiographically may be shown to be insignificant with FFR, or vice versa.

Background

Coronary artery disease (CAD) is a major cause of morbidity and mortality in the United Kingdom. It accounts for approximately half of all cardiovascular related deaths annually and, according to statistics from the British Heart Foundation, CAD related expenditure was £3,500 million in 2003 alone. Much effort has been placed on improving methods that detect and assess the severity of CAD and facilitate more rapid and appropriate management for CAD patients. Once diagnosed, CAD may be treated in 3 ways: (1)tablets alone, (2)tablets plus angioplasty with stents or (3) tablets plus coronary artery bypass graft surgery (CABG). The method of choice depends primarily on the extent and severity of disease at the time of coronary angiography. Coronary angiography is the current conventional method for the diagnosis of CAD and is used in the assessment of disease severity. For the angiographic procedure,vascular access is secured via the femoral artery or radial artery route and a dye is injected into the coronary artery blood vessels. The progress of the dye through the coronary blood vessels provides a visual assessment of where narrowings are present in the coronary arteries.

Where there is thought to be significant flow obstruction, particularly in symptomatic patients, one of the above three treatments will be offered.

While coronary angiography has revolutionised the management of CAD, the procedure is not without limitation. The purely visual assessment of disease severity with coronary angiography is subjective and patient management can depend on the cardiologist reviewing the films. Many such narrowings can be graded 'moderate' severity and deciding whether these are of haemodynamic significance is notoriously difficult by angiography alone. In recent years, the Radi pressure wire has been shown to provide accurate physiological haemodynamic data about coronary narrowings. Furthermore, the FFR measurement derived predicts clinical outcome, hence giving a 'cut-off' measurement for severity of disease that correlates with the requirement for revascularisation with either stents or surgery. Thus FFR is now frequently used in clinical practice by interventional cardiologists to decide if narrowings require treatment. However, the majority of diagnostic angiography in the UK is performed by non-interventional cardiologists who do not currently have access to the pressure wire technology. In this study, we speculate that if we measure the FFR routinely in all the main coronary arteries of patients undergoing coronary angiography the FFR data obtained may affect the angiogram-derived management of some patients in terms of the choice of tablets/stents/CABG. For example, some narrowings that look significant angiographically may not be haemodynamically important by FFR and vice versa. Clearly this could make a difference between revascularising a patient or not.

Research Aims

To evaluate:

1. The degree of correlation between standard angiographic assessment of the coronary arteries and pressure wire assessment of the main arteries.
2. To determine whether the FFR data would influence the management strategy for patients as derived only on the basis of the angiogram (which represents clinical practice).

Methods and Design

The study will recruit 200 patients listed for diagnostic coronary angiography performed by a non-interventional cardiologist.

Methodology 1: In Catheter Laboratory

• All patients will receive an information sheet after initial invitation to take part.
• Written informed consent will be obtained.
• Patients will undergo coronary angiography in a routine manner.
• The non-interventional cardiologist in charge of the patient's care will analyse the pictures and grade the outcome in the manner shown in table 1. He/she will formulate a management plan consistent with their routine clinical practice and independent of subsequent pressure wire data. This management plan will be documented in the CRF. He/she will then take no further part in the procedure.

Table 1

1. Are there significant stenoses (>70% by eyeball) in the major epicardial vessels (i.e. main coronaries or any branch of >2.25mm)
2. Recommend revascularisation or medical/conservative treatment
3. If revascularisation: recommended strategy for referral (Percutaneous Coronary Intervention (PCI) or CABG?) and which vessels (i.e. LAD + RCA etc) represent targets for that revascularisation

• The management strategy will be recorded according to the following options:

1. medical;
2. PCI
3. CABG

• Data will also be collected in regard to vessels as targets (i.e. which vessels require stent/graft)
• If the non-interventional cardiologist cannot make a plan they can allocate the patient to a fourth category in which "more data are required". Such patients are generally then referred for further non-invasive stress imaging or even for a pressure wire.
• FFR measurements will then be undertaken by a consultant interventional cardiologist
• Additional screening time and contrast use accrued during FFR measurements will be recorded.
• The patient will be given 70units/kg heparin i.a. or i.v. prior to passage of the pressure wire
• A pressure wire will be introduced into the distal third of all patent major epicardial coronary arteries and branches of >2.25mm with TIMI 3 flow.
• FFR measurements will be taken using either intracoronary or intravenous adenosine according to local conventional practice and operator preference.
• The protocol mandates i.v. adenosine for ostial LM stem and ostial RCA stenoses.
• Where i.c. adenosine bolus is employed, the minimum data required by the study is: 1 baseline FFR without adenosine and 2 boluses with at least 50mcg adenosine.
• An angiogram will be acquired before the first adenosine measurement to document satisfactory engagement of the guiding catheter and the position of the measurement in each vessel
• The minimum FFR reading will be taken in each case
• FFR readings of <0.8 will be considered as representing haemodynamic significance as per FAME protocol
• Once the FFR data are derived the procedure will be finished and haemostasis will be achieved in the normal manner
• Provided the angiogram-derived management plan has been recorded in the CRF then the FFR data can then be revealed to the non-interventional cardiologist. The management plan will then be recorded in the light of the FFR data using the same categories and dataset as previously.
• The non-interventionalists will then manage the patient as they see fit

Analysis

PRIMARY ENDPOINT Estimation of number of cases where FFR data results in a change in the management strategy the revascularisation strategy (number of vessel requiring treatment and/or PCI vs medical vs CABG)

Potential Clinical Value

If this study proves its hypothesis, it will suggest that coronary angiography would be better supported by routine pressure wire assessment in order to tailor revascularisation strategies for individual patients more accurately. The result of this study will carry important clinical implications if the study hypothesis is proven.... not least in terms of potential patient benefit. The current widely held practice of diagnostic test followed by either (i) referral for revascularisation or, (ii) in the case of equivocal angiographic results, referral for stress imaging to look for objective evidence of ischaemia followed by referral for revascularisation where positive could be rendered obsolete by diagnostic angiography performed by interventional cardiologists with FFR availability and the ability to perform PCI at the same sitting where appropriate.

The study may generate the hypothesis that such routine FFR measurement will not only be of benefit to patients but also be cost-effective if there would have been fewer interventions overall (ie less CABG + PCI) or fewer expensive interventions (i.e. less CABG versus PCI)?