Pre-operative risk assessment in redo cardiovascular surgery using high resolution computed tomography

B. Rosser, N. Cheshire, S. Mirsadraee Royal Brompton Hospital
Sydney St
London SW3 6NP



Opening the front of the chest for a second or subsequent time (redo-sternotomy) in order to perform further surgery on the heart, aorta or other great vessels is one of the most important contributors to operative complications in cardiovascular surgery. Injury to the vital organs lying directly under the breast bone (sternum) is the biggest risk. Scarring following previous surgery can cause some of these structures to stick closely to the under surface of the bone (post-operative adherence), putting them at particular risk of injury when the bone saw is used to reopen the sternum.

Several techniques are currently in use by cardiovascular surgeons to minimise or manage injury in redo sternotomy, up to and including patient cooling and cardiac arrest prior to re-opening. However there is no consensus on the best approach nor when to use a particular technique. Very little is written in the literature to describe common patterns of adherence of the vital organs lying under the sternum following previous surgery nor whether there are differences between adherence patterns in different groups of patients. Describing patterns of organs most commonly at risk in redo surgery may help in defining strategies to minimise organ injury.

Contemporary high resolution computed tomography (CT) provides excellent quality imaging of the under surface of the sternum with recognised spatial resolution of approximately 0.5mm. CT scans accurately define all of the most important organs lying under the sternum including the chambers of the heart (right ventricle and right atrium), the right coronary artery, the aorta and the innominate vein. CT scanning can clearly define the bony under surface of the sternum.

In this study we used high resolution CT imaging in a series of patients undergoing redo surgery at our institution to assess the most common patterns of vital structure adherence to the under surface of the sternum. We defined close adherence and risk of injury as any major organ at or less than 2mm from the under surface of the sternum. This new definition was developed as a result of structured questioning of experienced cardiovascular surgeons within our department.

This initial report concerns our overall findings and a comparison of the pattern of adherent organs seen in standard adult cardiac surgical patients (adult cardiac) with those seen in adult patients with inherited conditions affecting the heart and great vessels - adult congenital heart disease (ACHD).

We also studied where on the sternal under surface adherence was most common (using a grid to divide the sternum into 6 equal sections) and the surface area extent (mm2) of adherence. The results of these studies will be reported separately.

Method: The study was approved by our institutional Audit and Governance committee.
We studied 136 consecutive patients who underwent CT scanning prior to repeat sternotomy for

cardiac surgery between 01/2019 and 02/2021 and analysed the images regarding vascular structures equal to or within 2mm to the deep border sternum border in a structured way. We compared patients undergoing redo surgery for degenerative cardiovascular conditions (adult n=75) with adult congenital heart disease patients (ACHD n=61).

Results: In the ACHD group the right ventricle was the structure most commonly at risk of injury (2mm proximity). This occurred in 46.7% of patients. The innominate vein was the next most common structure at risk - 28% of the group. Other structures at risk were the right coronary artery (26% of patients) and the aorta (23% of patients). Only 32% of the ACHD group had no major organ 2mm of the sternum.

In the adult cardiac group, the right ventricle and innominate vein were also the most commonly found to be at risk of injury (54% and 25% of patients respectively). Proximity of the right coronary artery or aorta was only found in 5.3% (combined) of the adult patient cohort.

Further, within the ACHD patients a correlation between previous surgery involving the right ventricular outflow tract and proximity of the right ventricle at time on CTA was shown.
These findings show that there is a very high incidence of adherence of major organs to the under surface of the sternum in patients in our institution undergoing redo surgery. Using a newly developed definition of ‘at risk’ we believe these findings indicate organs which may be inadvertently injured during redo sternotomy. The right ventricle and the innominate vein are the most common structures at risk – in 50-75% of patients in both adult and ACHD groups. In the ACHD group, right ventricular adherence is most commonly seen following previous surgery to that chambers outflow vessel.

There are potentially important differences in patterns of adherence to the under surface of the sternum when comparing adult cardiac and ACHD populations. Adherence and injury risk to the aorta and the right coronary artery were much higher in the ACHD population compared with the adult cardiac population in this study.