TCD Detection of Gas and Solid Micro-Emboli in Patients Undergoing Coronary Artery Bypass Grafting (CABG): The Influence of Proximal Anastomosis Technique

It is not uncommon for a cardiac surgical patient to have his heart fixed but his brain damaged. Sometimes the damage is overt and manifests itself as a major neurological deficiency. The frequency of stroke, the so called type 1 damage, is reported to be between 1 and 4 percent. This may increase mortality from 1.4% to 22% and hospitalization from 6.6 days to 17.5 days. Diffuse encephalopathy, presenting as delirium, confusion, coma and seizures, so called type 2 damage, is reported to appear in a much higher frequency of 3% to 7%, depending on timing and methods of evaluation. This type of damage will increase mortality from 1.4% to 7.5% and hospitalization from 6.6% to 15.2%. Sometimes it is more subtle and appears as neurocognitive decline. This type of damage may be found in 53% of the patients at discharge, in 24% after six months and the frequency rises again to 42% at five years. The impact on the patient and his family might be devastating and the burden on the medical system and society enormous. Long term, moderate to severe disability may affect 69% of the stroke patients and survival may decline to 67% after one year.

After years of research efforts it became evident that inadequate global blood flow to the brain is relatively uncommon and cerebral hemorrhage is a rare cause of brain damage during cardiac operations. It also became evident that one of the most important damage mechanisms is embolization to the brain and the inflammatory response which amplifies the ischemic embolic damage. Looking for possible embolic sources by monitoring embolic signals (HITS) on the transcranial doppler (TCD) tracings, researchers found that manipulation of the aorta during cardiac surgery, like cannulation and especially clamping is a major source of emboli. Using the side biting clamp while performing proximal anastomosis has the potential to crush the aortic wall and release macro and micro emboli especially when the aorta is atherosclerotic. Using a single cross clamp technique might eliminate the aortic wall solid debris but introduce air emboli instead.

Dealing with the same problem, a few proximal anastomotic devices have been introduced and most of them withdrawn from the market because of inferior patency rate. The Heartstring proximal anastomotic device is one of the recently introduced devices for which early good patency rate has been demonstrated. The advantages, in terms of less brain embolization or improved neurologic outcome, have never been demonstrated for the Heartstring or any other anastomotic device.

A recent potential breakthrough in this field of emboli research and prevention in order to improve neurologic outcome after cardiac surgery is the introduction of the EmbodopR system by DWL. This is a high quality TCD system which has been further developed to monitor cerebral emboli. It contains a module which automatically screens every event suspected as embolic, eliminates those recognized as artifacts according to four different criteria and records only real embolic events. Another module can differentiate every event as gas or solid emboli by simultaneously insonating the middle cerebral artery blood with tow ultrasound beams, each of different frequency. The result is a new ability for real time monitoring and characterization of embolic events during cardiac operations.