Invasive aortic pressure and flow velocity measurements. Invasive aortic blood pressure and flow velocity measurements were carried out by Xx Xxxxx Xxxxx during cardiac catheterisation at St Xxxxxx’ Hospital cardiothoracic unit in patients undergoing clinically indicated angiography and/or angioplasty for the investigation/treatment of coronary artery disease. Following routine preparations for angiography, vascular access to the right femoral or radial artery was established with a 6Fr haemostatic sheath. A 6Fr-guiding catheter (JL4, Boston Scientific, UK) was advanced to the aortic root over an 0.35” wire using standard techniques and connected to a closed flushing system with a haemostatic valve. All subjects were systemically heparinized with unfractionated heparin (Wockhardt, UK) to reduce the risk of thrombus formation within the catheter. A Combowire pressure and Doppler flow velocity transducer (9500XT, VolcanoCorp, USA) was passed through the guiding catheter and the tip of the wire was positioned under fluoroscopic guidance in the proximal aortic root to obtain optimal coaxial stable pressure and flow tracings. The transducer was connected to a monitor (Combomap, VolcanoCorp, USA) with an analogue output at a frequency of 1 kHz and the signals were recorded via an analogue to digital converter (Micro 1401, Cambridge electronic design, UK). Aortic root pressure and Doppler flow velocity were obtained over at least 10 cardiac cycles at baseline and following administration of drugs (see below). All measurements were taken before the administration of ionic contrast agents for the subsequent angiogram or angioplasty except for a subset of subjects receiving intra-coronary drug infusions where diagnostic coronary angiography was performed before the research study to ensure the absence of significant left main stem or critical left anterior descending coronary artery disease that could affect the distribution of drug within the left ventricle. The aortic Doppler flow velocity waveforms were integrated over time and multiplied by aortic cross-sectional area (estimated from body surface area) to obtain a measure of stroke volume and hence cardiac output and total systemic vascular resistance.
