Tuesday, July 17, 2007

My week in Cardiothoracic Surgery

This past week I managed to observe some interesting cases in the cardiothoracic surgery O.R. After weeks of unsuccessful attempts to make connections, I finally was able to observe what I anxiously longed to see. I observed the replacement of coronary artery( CABG), pronounced 'cabbage', mitral valve, and aorta valve. Through all these cases, I was continually amazed by the enormous ability of myocardium to pump blood and the wealth of knowledge of the cardiosurgeon. The high level of organization and demand required in the cardiothoracic OR calls for highly competent teams of cardiologists, anesthesiologists, and cardiac perfusionologists. For the sake of brevity, I will describe some of the procedures involved in the open heart surgery.

Coronary Artery Bypass Graft (CABG) surgery

Approximately 500, 000 cases are performed in the U.S every year. The primary of cause of Coronary artery disease (CAD) is the deposition of cholesterol around the coronary artery, causing atherosclerotic plaque (hardening of the arteries). Other causes including high blood pressure, elevelated cholesterol, and diabetes.

Heart Attack illustration - Coronary Artery Bypass Graft Surgery

A patient suffering from this CAD can be diagnosed by obtaining electrocardiograms (EKG) of the heart and by performing stress test(treadmill)


Cardiosurgeon at Work...

Coronary Artery Bypass illustration
Depending on the severity of arterial plaque, the surgeon can perform Single, Double or a Triple coronary bypass. The blood vessels used as grafts are harvested from femoral artery or veins from the patient which are obtained laparoscopically (minimally invasive).

Once the patient has been put under anesthesia and intipated, the anesthesiologist inserts leads for echocardiogram to monitor the heart function and another set of lead electrodes to monitor brain function. Monitoring the brain and renal function are essential ensuring that the patient do not suffer significant ischemia once the heart(myocardium) has been stopped..After the pericardium(heart sac) has been exposed and the location to be operated identified, blood from the vena cava( de-oxygenated) and the blood from the lungs(0xygenated) are re-directed to the bypass machine. The heart is then injected with high K solution to stop it. The bypass blood is maintained at a certain perfusion pressure and the blood cooled down to 25 degree to reduce metabolic activity and reduce ischemia to the brain. Again, renal function is quite indicative of any significant ischemia. So before the surgeon operates on the heart, it is completely stopped and chilled to 4 degree with ice slush. You can see the myocardium contract slightly after it has been cut...Really cool!

In the figure below, the blood is cannulated by tapping into the topmost superior vena cava and the aorta.

Illustration of a Healthy Heart Cross-Section


At a 40-min time interval while the heart is stopped, it is injected to high K solution to 'sedate' it. The heart ideally should not be injected over 3 times which means that the surgeon has to try to stay within a 120-min window within which the heart has been stopped. Everything is hectic during this time, with the surgeon instructing all the concerned to carry out different tasks, warm the body, add anti-coagulants, increase perfusion pressure, and etc...

Once the grafts have been sutured, the heart and the body are warmed to the physiological temp. and then heart is resuscitated by shocking it. At this point, it is a matter of ensuring that the heart beats properly before the blood is redirected from the bypass machine and the patient is sutured to ensure there is no bleeding. I couldn't believe seeing the heart beat again..wowoow. I will blog about the valve replacement in my next blog..


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