Intermittent arm cuff inflation reduces the extent of heart muscle injury at the time of cardiovascular injury. The intervention is known as remote ischaemic conditioning (RIC) however the mechanisms by which RIC acts are incompletely understood. One mechanism that might explain the benefits of RIC is an improvement in coronary artery function which in turn might help improve blood flow to heart muscle.
The primary aim is to determine whether intermittent inflation of a blood pressure cuff for 5 min periods at 200 mmHg on 4 occasions separated by 5 minute intervals can improve coronary vascular function compared to cuff placement with no cuff inflation. A secondary aim is to determine whether or not RIC alters the circulating concentrations of small molecules and hormones in systemic blood that regulate coronary endothelial function.
The investigators will perform a randomised controlled trial of RIC in a minimum of 60 patients with known or suspected angina and in whom coronary angiography with angioplasty would be considered. A screening log will be prospectively recorded. In order to be enrolled prior knowledge of the coronary anatomy and disease is necessary, and this information can be obtained by screening referrals for invasive angiography following non-invasive CT coronary angiography, or staged invasive management when angioplasty is intended following initial invasive angiography.
The protocol had initially involved two coronary angiograms with coronary reactivity testing on the same day, with the first angiogram taking place before the RIC-COR intervention and the second angiogram taking place immediately afterwards. However, after enrolling 10 participants it was evident that the total procedure time and hospital stay was unduly long and impractical. Therefore, following consultation with the trial biostatistician, funder and ethics committee, the protocol was amended and the initial angiogram was removed (May 2012). There were no other changes to the study design. Following a change in service arrangements for elective referrals for coronary angioplasty in our hospital, and constraints around staff illness and availability, recruitment was temporarily suspended on logistical grounds (September 2013 to November 2014).
Following informed consent before the invasive procedure, the patient will be randomly assigned to the intervention group (cuff inflation protocol) or the control group (cuff placement, no inflation; sham protocol). The clinical team will be blind to treatment group assignment.
Clinically-indicated coronary angiography will be performed first, including administration of glyceryl trinitrate (200 - 400 micrograms; short acting preparation) to attenuate coronary artery tone. Based on the angiographic findings, the cardiologist will select a coronary artery with minimal or no evidence of coronary artery disease.
Endothelial function will then be assessed in this artery by intra-coronary infusion of acetylcholine (ACh) in incremental doses. Non-endothelium dependent vasodilation will be assessed using intra-coronary administration of glyceryl trinitrate at the end of the infusion protocol.
An infusion catheter will be used to selectively instrument the coronary artery of interest. The factors that influence the selection of a coronary artery for study include 1) minimal or no angiographic evidence of coronary disease, 2) practical considerations for insertion of an intra-coronary catheter ie. vessel tortuosity, calibre. The coronary reactivity protocol involves intra-coronary administration of study drug at a rate of 2 ml/min for 2 minutes in the following order: 1) 0.9% normal saline; 2) ACh 10-6 Molar (M), 3) ACh 10-5M, 4) ACh 10-4M, 5) 0.9% normal saline; and finally, 6) bolus intra-coronary administration of 200-400 micrograms of glyceryl trinitrate. The patient's clinical response will be assessed prospectively, including with continuous haemodynamic recording (heart rate, rhythm, conduction and aortic blood pressure). A 12-lead electrocardiogram (ECG) and cine coronary angiogram will be obtained synchronously at baseline, at the end of each 2 minute infusion, and following nitrate administration.
Coronary diameter will be measured after the procedure using computer-assisted quantitative coronary analysis (QCA) with custom software (eg Medis, Leiden, Netherlands), by a trained observer blinded to the allocated group. The coronary segment for analysis will be located distal to the infusion catheter in the proximal - mid segment of the right coronary artery or a main branch of the left coronary artery. The segment will have minimal or no angiographic evidence of coronary disease. The length of the segment will be 30 mm. The same angiographic projection will be used for all of the analyses. The software will be calibrated on the catheter. Mean lumen diameter and mean coronary area will be computed.
Epicardial spasm, defined as \>90% reduction in coronary artery diameter with ischaemic ST-segment changes on the ECG, and microvascular spasm, defined as ischaemic ST-segment changes without epicardial coronary vasoconstriction \>90% will be assessed.
ECG changes, including alterations in atrio-ventricular conduction and ST-segment deviation, will be prospectively recorded.
Since a neuro-hormonal response may potentially mediate RIC, a blood test will be performed before and after cuff placement in all patients (active and control groups) to measure circulating molecules known to regulate blood vessel function.
The study data will be analysed by a biostatistician who is independent of the research team.
If the investigators can discover the effects, if any, of RIC on coronary vascular function, then potentially this information would provide new insights into the mechanisms of action of RIC.
