**2.2 Assessment of the aorta**

Surgeons traditionally assess the aorta by manual palpation prior to the placement of the cannula and clamp. This is problematic because it relies on the detection of calcified plaques in the wall of the aorta that are accessible to the finger; which predominantly reflects the anterior and right sides of the ascending aorta, and anterior aspect of the aortic arch. Other areas of the aorta are really not accessible or not easily accessible to manual palpation. The detection of calcified plaques infers resistance being offered to the surgeon's finger, and our previous data found that detection of such plaques was relatively accurate under these circumstances. What are not accurately detected are soft (not calcified) plaques, which do not offer counter resistance to the examining finger. However the propensity of these to disrupt and embolise the contents or components is potentially greater than for calcified plaques. Thus the manual examination of the ascending aorta by the surgeon should be considered as frequently inaccurate (Royse, Royse et al. 2000; Royse, Royse et al. 1998; Suvarna, Smith et al. 2007; Sylivris, Calafiore et al. 1997; Whitley and Glas 2008).

Transoesophageal echocardiography is not able to visualise the distal ascending aorta or the proximal aortic arch. This is because the distal trachea and right main bronchus lie between oesophagus and these structures, and so the ultrasound signal is not transmitted leading to poor or absent imaging. Furthermore, the anterior aortic wall is further than near structures in relation to the probe, further diminishing resolution. Yet the most frequent locality for placement of the aortic cannula for cardiopulmonary bypass is in the distal ascending aorta proximal or aortic arch. Equally, the aortic clamp is placed immediately proximal to the aortic cannula whereby there is substantial aortic manipulation. Thus, the key areas of aortic manipulation related to the use of cardiopulmonary bypass occur in the "blind spot" of transoesophageal echocardiography.

This point was reinforced by a meta-anaylsis performed by van Zaane comparing transoesophageal vs. epiaortic echocardiography (Van Zaane, Zuithoff et al. 2008). Transoeosphageal had a sensitivity of only 21% (95% confidence interval (CI) 12-32%); but a specificity of 99% (95% CI 96-99%). Simply TOE is accurate at assessing the aorta that can be visualised, but not all of the aorta can be imaged. Therefore, the accurate assessment of all parts of the thoracic aorta require a combination of transoesophageal and epiaortic (epivascular) surface ultrasound.

#### **2.3 The precise anatomical location of aortic atheroma**

Of critical importance to the use of epiaortic ultrasound, is the ability to precisely locate atheroma in relation to anatomical landmarks. The use of TOE provides for relative anatomical locality by finding lesions relative to the locality of other landmarks seen, such as the aortic valve. TOE alone will therefore lead to imperfect localisation of the aortic atheroma; whereas use of a handheld probe provides definitive locality of aortic atheroma (since the lesion is present immediately beneath the probe). This is crucial when precise locality on cannulation or clamping is required in order to avoid atheroma.

### **2.4 Prevalence of thoracic aortic atheroma**

Surprisingly, coronary bypass patients do not uniformly have aortic atheroma, even in the presence of extensive small vessel arterial disease. But the danger for surgeons (and

Surgeons traditionally assess the aorta by manual palpation prior to the placement of the cannula and clamp. This is problematic because it relies on the detection of calcified plaques in the wall of the aorta that are accessible to the finger; which predominantly reflects the anterior and right sides of the ascending aorta, and anterior aspect of the aortic arch. Other areas of the aorta are really not accessible or not easily accessible to manual palpation. The detection of calcified plaques infers resistance being offered to the surgeon's finger, and our previous data found that detection of such plaques was relatively accurate under these circumstances. What are not accurately detected are soft (not calcified) plaques, which do not offer counter resistance to the examining finger. However the propensity of these to disrupt and embolise the contents or components is potentially greater than for calcified plaques. Thus the manual examination of the ascending aorta by the surgeon should be considered as frequently inaccurate (Royse, Royse et al. 2000; Royse, Royse et al. 1998;

Suvarna, Smith et al. 2007; Sylivris, Calafiore et al. 1997; Whitley and Glas 2008).

Transoesophageal echocardiography is not able to visualise the distal ascending aorta or the proximal aortic arch. This is because the distal trachea and right main bronchus lie between oesophagus and these structures, and so the ultrasound signal is not transmitted leading to poor or absent imaging. Furthermore, the anterior aortic wall is further than near structures in relation to the probe, further diminishing resolution. Yet the most frequent locality for placement of the aortic cannula for cardiopulmonary bypass is in the distal ascending aorta proximal or aortic arch. Equally, the aortic clamp is placed immediately proximal to the aortic cannula whereby there is substantial aortic manipulation. Thus, the key areas of aortic manipulation related to the use of cardiopulmonary bypass occur in the "blind spot" of

This point was reinforced by a meta-anaylsis performed by van Zaane comparing transoesophageal vs. epiaortic echocardiography (Van Zaane, Zuithoff et al. 2008). Transoeosphageal had a sensitivity of only 21% (95% confidence interval (CI) 12-32%); but a specificity of 99% (95% CI 96-99%). Simply TOE is accurate at assessing the aorta that can be visualised, but not all of the aorta can be imaged. Therefore, the accurate assessment of all parts of the thoracic aorta require a combination of transoesophageal and epiaortic

Of critical importance to the use of epiaortic ultrasound, is the ability to precisely locate atheroma in relation to anatomical landmarks. The use of TOE provides for relative anatomical locality by finding lesions relative to the locality of other landmarks seen, such as the aortic valve. TOE alone will therefore lead to imperfect localisation of the aortic atheroma; whereas use of a handheld probe provides definitive locality of aortic atheroma (since the lesion is present immediately beneath the probe). This is crucial when precise

Surprisingly, coronary bypass patients do not uniformly have aortic atheroma, even in the presence of extensive small vessel arterial disease. But the danger for surgeons (and

locality on cannulation or clamping is required in order to avoid atheroma.

**2.2 Assessment of the aorta** 

transoesophageal echocardiography.

(epivascular) surface ultrasound.

**2.3 The precise anatomical location of aortic atheroma** 

**2.4 Prevalence of thoracic aortic atheroma** 

patients) is assuming that the presence of important aortic atheroma is predictable. Indeed the unpredictability of the presence, location and severity of aortic atheroma is the most powerful argument in favor of routine comprehensive ultrasound examination of the entire thoracic aorta being performed. Specifically, the absence of atheroma seen in the descending aorta or proximal aorta by TOE does *not always predict* the absence of clinically important atheroma in the distal ascending aorta or proximal arch (the TOE "blind spot") (Royse, Royse et al. 1998).

We described six zones for the thoracic aorta; three in the ascending aorta, two in the aortic arch and the descending aorta. TOE typically images zones 1-2 and 5-6 well; and epiaortic echocardiography images zones 1-4 well. For reference, most aortic cannulations and clamping occurs in zones 3-4; proximal aortic graft anastomoses in zone 2 and aortic incision for valve replacements in zone 1. An intra-aortic balloon pump will be deployed in zone 6. Within these zones, the site of the atheroma is further subcategorised into cross sectional quadrants of the aorta - anterior, posterior, left or right lateral.

We found that the prevalence of atheroma increased with distance from the aortic root. There was a marked increase in frequency and severity distal to the aortic arch. Increasing age resulted in greater prevalence. Considering moderate or severe atheroma in zones 1-4, the prevalence was 29% in patients aged 70-79, and 34% in those aged more than 80 years (Royse and Royse 2006).

### **2.5 Assessment of aortic atheroma severity**

A variety of definitions have been published, but most commonly this simple classification is used, Table 1 (Royse, Royse et al. 1998). The greater the severity of atheroma, the greater the likelihood that manipulation will result in embolism; excepting that most believe embolism is unlikely to arise from "mild" atheroma. In clinical practice the term "clinically important atheroma" generally refers to moderate or severe atheroma.


Table 1. Classification of atheroma grade

The morphology of the atheromatous plaque may further predict the likelihood of embolism. Without good data, it would seem intuitive that a soft friable, frond-like atheromatous plaque is more likely to break free and embolise, than a flat, fibrous plaque.
