Cerebral Complications of Cardiac Surgery - An Insight

Introduction:

Cardiac surgery or heart surgery is a life-saving treatment option in some cases. However, this also poses a risk for various neurological complications post-surgery. Elderly populations are at maximum risk for heart diseases, and with co-existing systemic diseases, the risk of surgery increases even more in such patients. These complications can be mild such as problems with balance and coordination, speech problems, and vision problems, or even may be as severe as seizures (uncontrolled movements of the body accompanied by loss of consciousness) and coma (it is a state of prolonged unconsciousness with no response to external stimuli).

What Are the Different Types of Cardiac Surgery?

Cardiac surgery is the surgical treatment of pathologies associated with the heart. The following are the different cardiac surgeries -

1. Coronary Artery Bypass Graft (CABG) - This is the most commonly carried-out cardiac surgery. It is done to create a new path for blood to flow past a blocked coronary artery. The surgeon makes use of a healthy artery or vein from another place in the body and connects it adjacent to the blocked artery (bypasses the blocked artery) to maintain the blood supply to the heart. This surgery is commonly known as heart bypass surgery.
2. Pacemaker Insertion - Cardiac arrhythmias or irregular heartbeat indicates pacemaker implantation. In this condition, the heart may beat faster or slower than usual. It is due to imbalances in the electric signals that control the beating of the heart. This condition can be treated with drugs, but if drugs do not seem to work, the surgeon places a device under the skin of the chest of the patient known as a pacemaker. This device is connected to the heart with tiny wires. This device detects the irregular rhythm of heartbeats and sends electrical signals to regulate the heartbeat.
3. Maze Surgery - It is used for treating atrial fibrillation (the irregular rhythm of the heart). The human heart has four chambers (two upper and two lower) known as atriums. In this surgery, the surgeon manually creates scar tissue in a maze-like pattern in the upper chambers of the heart or with the help of any device.
4. Aneurysm Repair - An aneurysm is a bulge in the wall of the artery that enlarges, stretching the artery's walls. An aneurysm can rupture and bleed. Patients with elevated blood pressure are at increased risk for developing aneurysms. Aneurysm repair may require surgery to open the chest or abdomen to repair the aneurysm. Endovascular aneurysm repair is a new minimally invasive technique to repair an aneurysm.
5. Insertion of a Ventricular Assist Device (VAD) or Total Artificial Heart (TAH) - It is a mechanical circulatory support device that aid in pumping blood from the lower chambers of the heart to the rest of the body. Implanting this device in one of the ventricles (left or right) requires open heart surgery. This surgery is performed in patients waiting for a heart transplant or who cannot have a heart transplant due to risk factors such as age and other systemic diseases.
6. Heart Transplant - It is the complete replacement of the diseased heart with a healthy heart that a deceased donor donates.
7. Heart Valve Repair or Replacement Surgery - The human heart has four valves (mitral, tricuspid, aortic, and pulmonary) that control blood flow. They prevent the backflow of blood and help it move in one direction. In this surgery, the surgeons either repair the damaged valve or replace it with an artificial or a biologically derived valve (valves of cows, pigs, and humans).

What Are the Different Neurological Problems Associated With Cardiac Surgery?

The different neurological symptoms depend on which part of the brain is damaged during surgery. The general signs of brain damage post-cardiac surgery are -

1. Problems With Balance and Coordination - Damage to the cerebellum (posterior portion of the brain) will lead to poor movement control.
2. Speech and Memory Problems - The side parts (temporal) of the brain are responsible for functions such as memory and hearing. Injury or damage to the temporal lobe of the brain will lead to these problems.
3. Mental Confusion - The front part of the brain (frontal lobe) is associated with speech, personality, and emotions. Damage to this part of the brain may lead to difficulty in concentration.
4. Blurred Vision - The rear part of the brain (occipital lobe) is responsible for vision. Damage to this portion can even cause loss of sight.
5. Seizures - Uncontrolled movements of the body accompanied by loss of consciousness.
6. Stroke - Patients undergoing coronary artery bypass graft surgery are at a high risk of stroke postoperatively.

Brain imaging scans of patients undergoing coronary artery bypass graft surgery show signs of ischemia (restricted or reduced blood flow and oxygen to a body part). This may be a cause of cognitive decline in these patients.

Who Is at a High Risk of Neurological Problems After Undergoing Cardiac Surgery?

Patients with chronic systemic diseases such as -

1. Hypertension (increase in blood pressure).
2. Diabetes mellitus (abnormal increase in the blood glucose level).
3. Patients with a positive history of stroke are more prone to develop neurological problems post-cardiac surgery.
4. Patients of advanced age are also at a high risk of brain injury.
5. Cardiac diseases such as aortic atherosclerotic disease (chronic buildup of plaque in the aorta) have a higher rate of postoperative neurological dysfunction and stroke.
6. Females are at a higher risk of brain injury post-cardiac surgery.

How Does Cardiac Surgery Cause Brain Injury?

Inflammation of the brain tissue causes damage to the brain. This can occur due to unexpected events at the time of surgery. Hypoxia (low oxygen levels) is the main cause of brain damage. It leads to ischemia which causes a stroke. Infarcts can cause reduced blood flow and lead to brain damage. Treating these infarcts requires cardiac surgery, which can further compromise the blood flow to the brain.

What Are the Measures Taken by Surgeons to Improve the Outcome of Cardiac Surgery?

1. Maintaining intraoperative blood pressure is essential.
2. Oxygen levels (90 %) are beneficial during cardiac surgery.
3. Hemoglobin levels are also kept in check during surgery.
4. Newer surgical techniques have been developed to make the surgery minimally invasive.

Conclusion:

Cardiovascular surgery is a common cause of neurological problems despite advances in surgical techniques. The surgeon needs to have a better knowledge of the undergoing surgery and the complications it will cause on the rest of the body. The surgeon should carry out a detailed pre-operative evaluation of pre-operative risk factors such as existing chronic systemic disease, patients with a history of neurological disorders, and are on drug therapy. Mild problems with cognitive function that may usually resolve by themselves a few weeks post-surgery.