Assessing the Efficacy of CARDIOgoniometry (CGM) to Determine Physiologically Significant Stenosis in Patients With Stable Coronary Artery Disease in Comparison to Fractional FLOW Reserve - CARDIOFLOW

This study aims to test the hypothesis that cardiogoniometry (CGM) is helpful to identify physiologically significant coronary artery stenosis in comparison to fractional flow reserve (FFR).

Last year in the UK 202 098 patients underwent coronary angiography to determine whether they had significant coronary artery disease. However, it is well recognised that, even with orthogonal views, angiography is limited in terms of its ability to determine the functional importance of coronary lesions. In particular those lesions judged to be 50-70% stenosed may not necessarily cause ischaemia as this depends on factors such as the lesion length and, importantly, the size of the territory supplied by the vessel.

There have been several studies that have demonstrated the clinical utility of evaluating such lesions with FFR. The measurement of FFR is an index of the physiological significance of a coronary stenosis and is defined as the ratio of maximal blood flow in a stenotic artery to normal maximal flow. It is calculated by comparing the ratio of the aortic pressure and the pressure distal to the coronary stenosis during maximal hyperaemia. These pressures are measured by introducing a coronary pressure guide wire into the artery and hyperaemia is induced by giving an infusion of adenosine intravenously. An FFR ratio of <0.80 indicates that the coronary stenosis is causing significant ischaemia and would benefit from PCI. This has since been incorporated into ESC clinical guidelines on myocardial revascularisation.

However this is an invasive procedure and the pressure wires are relatively expensive compared to standard angioplasty wires. On the contrary, CGM is a cheap and non-invasive technique that can be easily applied. The aim of the proposed study is to assess whether CGM may be able to aid clinicians in identifying if a coronary stenosis is physiologically significant at inducing myocardial ischaemia in conjunction with standard coronary angiography.

CGM is form of 3D vector electrocardiography which can provide quantitative analysis of myocardial depolarisation and repolarisation. It has been shown to be more sensitive and specific than standard 12-lead ECG at diagnosing stable coronary artery disease. Furthermore, other work has showed CGM to be more sensitive than 12-lead ECG at detecting patients with ACS. More recently in 2012, further work found that CGM was more sensitive and specific than the 12 lead ECG at identifying abnormal myocardial perfusion scans (MPS). FFR validity was initially based on a comparison with MPS and therefore we hypothesise that CGM may be comparable to FFR.

Inclusion criteria

• Patients admitted with stable coronary artery disease for elective percutaneous coronary intervention (PCI)
• Patients who have been consented to undergo coronary angiography +/- PCI as part of their routine care by their clinician.
• Aged 18 or over.
• The patient has been informed of the nature of the study and has provided full written informed consent.
• FFR will be performed on study participants who demonstrate visible coronary stenosis on coronary angiography.

Exclusion criteria

• Patients unable to give informed consent including those with communication difficulties due to poor English.
• Patients with haemodynamic instability and / or cardiogenic shock (defined as a sustained blood pressure of <90mmHg +/- the need for inotropic support)
• Patients with an acute coronary syndrome (as defined by the European Society of Cardiology)
• Those unable to perform a good quality CGM: 1) Patients who are SOB at rest; 2) Patients with very frequent ectopic beats; 3) Patients in atrial fibrillation; 4) Patients with a heart rate >150 beats/min
• Those patients unable to tolerate adenosine: 1) Patients with severe asthma, especially if taking oral theophylline; 2) Patients with second or third degree heart block (without a pacemaker in situ); 3) Patients with sick sinus syndrome; 4) Patients with Long QT syndrome; 5)Patients with severe hypotension (systolic pressure) <100mmHg); 6) Patients with decompensated heart failure.
• Patients with previous coronary artery bypass graft surgery
• Patients who are unable to receive treatment with heparin
• Patients with a chronic total occlusion
• Patients with extremely tortuous or calcified vessels that are unfavourable for assessment with FFR.
• Patients with severe stenosis of the left main stem
• Patients with significant renal impairment (defined as eGFR<30ml/min)
• Females who are or could be pregnant