Preoperative optimization of cardiac function using SvO2.

Preoperative risk assessment, before noncardiac surgery, aims to reduce mortality and morbidity, during the perioperative period. Cardiac risk could be minimised through treatment and stabilisation of the underlying disease, careful monitoring and prophylactic medications. However, cardiac complications, especially, ischemic events are still frequent causes of death during surgery and hospital recovery. A teamwork approach that involves cardiologist, anaesthesiologist and surgeon is required for optimal risk assessment and monitoring in the perioperative period. The incidence of coronary artery disease increases with age and with the presence of risk factors such as diabetes or hypertension. There is also a strong relation between coronary and vascular disease as they are part of the same pathophysiology and have common risk factors. Careful cardiac evaluation is essential when vascular surgery is planned. Clinical evaluation is the first step of preoperative risk assessment and allows the identification of low and high-risk patients. If there is absent or low cardiac risk, surgery may be carried out. In the presence of high-risk markers and if the surgery is elective, coronary arteriography should be considered before non-cardiac surgery. The information provided by non-invasive diagnostic testing is essential in those patients with an intermediate clinical risk for cardiac events. Concerning coronary artery disease, myocardial function and ischemic burden are strong prognostic markers and in this particular setting, nuclear cardiology can play an important role. The extent and localisation of ischemia is well defined by myocardial perfusion scintigraphy and ventricular function can be evaluated by radionuclide ventriculography or by gated perfusion studies.

Heart↗

PubMed2000

Photon energy recovery for crosstalk correction in simultaneous 99mTc/201Tl imaging.

UNLABELLED: Simultaneous 99mTc sestamibi/201Tl imaging enables the acquisition of images of myocardial stress perfusion and myocardial viability in a single process. One of the major limits of this technique is the crosstalk of the 99mTc downscattered photons into the 201Tl window. We propose using the spectral deconvolution technique photon energy recovery (PER) for correcting this crosstalk. METHODS: A planar line phantom made of 99Tc vertical lines and 201Tl horizontal lines and a cardiac SPECT phantom including an anterior (2 mL) and an inferior (1.5 mL) myocardial fixed defect were used. The phantoms were filled with an initial 99mTc/201Tl ratio of 5:1. Several successive acquisitions were made from time t = 0 to time t = 48 h (99mTc/201Tl ratio approximately 0) without moving the phantoms. Total number of counts, contrast, and normalized SD (NSD) were calculated on the Tl-raw and the Tl-PER planar images. SPECT datasets were analyzed. The Tl-raw images recorded at 48 h were considered the reference "virgin" 201Tl images. RESULTS: Total number of counts, contrast, and NSD ranged from 336% to 201%, 15% to 29%, and 257% to 225% of the virgin 201Tl values, respectively, for Tl-raw planar images; whereas values for Tl-PER images ranged from 128% to 108%, 61% to 79%, and 154% to 108%, respectively. Anterior and inferior defect contrasts ranged from 1.18 to 1.22 and 1.12 to 1.16 for Tl-raw SPECT images, respectively; whereas for Tl-PER images, value ranges were 1.28-1.32 and 1.21-1.24, respectively. The corresponding reference virgin 201Tl values were 1.31 and 1.25 respectively. Summed score, average defect severity, and average defect extent ranges were 4-5, 0.4-0.52, and 4.7-5.9 for Tl-raw images, respectively, and 8-9, 0.59-0.79, and 7.4-8.8 for Tl-PER images. The reference virgin 201Tl values were 9, 0.73, and 8.7, respectively. CONCLUSION: PER is quantitatively efficient to remove 99mTc crosstalk photons from 201Tl images for 99mTc/201Tl ratios ranging from 5:1 to 2:1.

Heart↗