Risk Stratification
Identification of vulnerable patients at increased risk of stroke before CABG is of paramount importance for the surgical decision-making approach and informed consent. The risk of stroke before CABG has been extensively scrutinised leading to the identification of several risk factors. Age, diabetes, hypertension, peripheral vascular disease, renal failure, left ventricular dysfunction and non-elective surgery have consistently been reported as risk factors of peri-operative stroke in patients undergoing CABG surgery.22,23 All these risk factors can be assessed before surgery, so the information can assist informed decision-making by patients, their family and their physicians. The combination of these variables has generated several risk stratification tools that can be implemented before surgery, to determine the individual probability of stroke in patients undergoing CABG.
In the Charlesworth score, generated from 33,000 consecutive patients undergoing isolated CABG, seven variables are integrated, including age, diabetes, left ventricular ejection fraction <40 %, female gender, priority of surgery, renal dysfunction and peripheral vascular disease.22 In the simpler model generated by McKhann et al. only three variables are considered: age, hypertension and history of stroke.6 More recently, Hornero et al. generated and validated a new risk model (Pack2 score), including priority of surgery, peripheral vascular disease, preoperative cardiac failure/left ventricular ejection fraction <40 % and chronic kidney failure.23 Interestingly, in patients with Pack2 score ≥2, off-pump CABG significantly reduced the risk of stroke compared with on-pump CABG, whereas no difference was apparent between the two strategies of revascularisation in patients with Pack2 score <2. Further studies should externally validate this score and assess whether it is useful in clinical practice to select the optimal strategy of revascularisation between on-pump and off-pump CABG in high-risk patients.
However, while these risk stratification tools are important because they factor the additive effect of several variables, they also share a major limitation in disregarding two important risk factors – atherosclerotic disease of the ascending aorta12 and pre-existing cerebrovascular disease.6 As the impact of these two factors on the risk of post-operative stroke is substantial, they should always be scrutinised before deciding the optimal strategy of coronary revascularisation.
Severe atherosclerosis of the ascending aorta is often an unexpected intra-operative finding during CABG, when preoperative risk stratification has not been accurate. It represents a challenge for the surgeon, who may need to change the operative strategy. A variety of methods can be used before surgery to diagnose severe atherosclerosis in the ascending aorta, including computed tomography scanning, transoesophageal echocardiography or magnetic resonance imaging. Intra-operative ultrasonographic scanning of the aorta can also be used to detect atherosclerotic changes in the entire ascending aorta. It is a rapid, safe and sensitive method, and some studies have reported that it is more accurate than both transoesophageal echocardiography14 and computed tomography in detecting atheromatous debris in the ascending aorta.24
Assessment of the neurological risk profile of patients before CABG is another essential step to make accurate risk stratification. The neurological profile of the patient should be carefully characterised, seeking for a history of stroke, the presence of initial neurocognitive disorders, or the presence of pre-existing cerebrovascular disease.6 Recent studies have also suggested that detection of cerebral ischaemia by magnetic resonance imaging before CABG is strongly associated with the risk of post-operative stroke.25,26 Screening of carotid artery disease with echo Doppler before CABG should also be performed, especially in high-risk patients.