2 The technology

Description of the technology

2.1 The MiraQ cardiac system (MCQ0, MediStim ASA) uses ultrasound for the non-invasive assessment of graft blood flow during coronary artery bypass graft (CABG) surgery. It is intended for use in patients with coronary artery disease who are having CABG surgery. It measures 3 parameters of transit time flow (mean blood flow in ml/minute, pulsatility index and diastolic filling percentage) to assess graft blood flow and check patency.

2.2 The MiraQ system measures transit time volume flow using specially designed probes. A microcomputer with a 19‑inch touch screen mounted on a moveable trolley is used to control the probes and store their outputs.

2.3 The MiraQ system can use 2 types of probes to assess blood flow during CABG procedures (the PS and PQ). These differ in the number of recommended reuses and their method of sterilisation. Only the PS probe is considered in this guidance, because the PQ probe needs ethylene oxide sterilisation, which is not thought to be widely available in the NHS. The probes deliver a bidirectional ultrasound beam across a target vessel and the system analyses the returning signal to calculate the blood flow through the vessel at a default filter setting of 20 Hz. A real-time flow curve is displayed together with the mean blood flow in ml/minute, pulsatility index and diastolic filling percentage. This information can be used to determine whether flow through the graft and its anastomoses is acceptable. If not, then the graft can be explored to detect imperfections and revised as necessary to achieve acceptable blood flow.

2.4 The cost of the MiraQ system stated in the sponsor's submission includes £32,000 for the VeriQ 2011 console, and £1,582 for each PS probe. These costs have been updated in the 2017 revision of the cost model to £34,000 for the cardiac MCQ0 console and £1,481 for each probe. [2018]

2.5 The claimed benefits of the MiraQ system in the case for adoption presented by the manufacturer are:

  • improved outcomes of revascularisation procedures by reducing the risk of early graft failure and adverse events

  • reduced hospital stay for some patients by reducing the incidence of complications during and after surgery

  • reduced numbers of repeat procedures and treatments for postoperative complications.

Current management

2.6 Coronary artery disease is a common cause of symptoms, disability and death. It is caused by atherosclerosis, which leads to stenosis or occlusion of the coronary arteries. NICE clinical guideline 126 on 'Management of stable angina' recommends that revascularisation of the blocked coronary arteries using CABG or percutaneous coronary interventions should be considered in people whose symptoms are not satisfactorily controlled by medical treatment.

2.7 CABG aims to bypass narrowed or blocked segments of the coronary arteries using grafts. Grafts are usually constructed from lengths of the patient's own long saphenous vein or their internal mammary artery, although other vessels are also used.

2.8 Cardiac surgeons use a variety of techniques to avoid technical imperfections during CABG, but assessment of graft flow is usually subjective. Techniques used vary according to the graft used, the surgical technique, and the surgeon's individual preference. They include the surgeon assessing resistance and perfusion beyond a graft by flushing fluid through it before restoring flow, and both observing and palpating grafts for pulsation when blood flow has been re-established.

2.9 There are a number of methods for the objective assessment of the technical results and of blood flow. Transoesophageal echocardiography evaluates heart function after bypass by assessing regional left ventricular wall motion abnormalities, which can be compared with preoperative regional left ventricular function. Perioperative graft flow can be visualised in the operating theatre using conventional angiography or using indocyanine green fluorescence. NICE has produced guidance on 'Intraoperative fluorescence angiography for the evaluation of coronary artery bypass graft patency' (interventional procedures guidance 98). This guidance states that 'current evidence suggests that the procedure is safe enough for routine use in the evaluation of coronary artery bypass graft patency'.

  • National Institute for Health and Care Excellence (NICE)