Cardiac Path Online
Post-Operative Cardiac Pathology-
"Death after Cardiac Surgery"
patients who die after procedures requiring cardiopulmonary bypass
present particular problems.
It is especially important to study the operation notes.
If necessary one should ask one of the surgical or intensive care team to explain what was done both during and after the procedure.
If heart is dissected by one of the commonly used techniques for example, following the flow of blood it will probably be unrecognizable to the surgeon after fixation.
The best technique is to inflate the left ventricle with formalin via the aortic valve, fix for 24 hours, and then make a single cut in the “echo” plane.
This can usually be adjusted to avoid the orifices of bypass grafts in the ascending aorta.
If this is not possible, the atria and ventricles can be opened by cutting carefully along each side of the posterior interatrial and interventricular septae.
The cut should be extended only to the apex, leaving the anterior surface of the heart unscathed.
The aortic valve is exposed by trimming off the aorta just above aortic annulus.
The coronary ostia can then be inspected and the coronary arteries dissected.
The most frequent cause of death is usually acute cardiac failure and in almost half of these there is usually evidence of recent myocardial infarction.
Other causes included chronic heart failure, cardiac, gastrointestinal or intracerebral haemorrhage and pulmonary embolism.
Coronary artery bypass grafting (CABG) is now the commonest cardiac surgical procedure.
The determination of the precise cause of death after these procedures is very difficult and in one series no obvious explanation was found in a number of cases.
When acute infarcts occur after CABG almost all are in the area supplied by the vessel into which the graft has been inserted.
Transverse sections should be taken through each of the anastomoses and examined carefully for thrombus formation.
Histology should be taken of the anastomosis and of the left ventricular muscle distal to the graft.
The macroscopic appearances of heart muscle can be very deceptive and it would be difficult to identify the edge of an infarct without histology.
Many vessels on the anterior surface of the heart are now bypassed with internal mammary artery graft.
This vessel is dissected from the anterior chest wall from close to its origin from the left subclavian artery.
Clumsy removal of the sternum or cutting of the rib case may cause artifactual damage to these grafts.
Many centers now use bilateral internal mammary grafts and in these patients there may be an increased incidence of sternal wound breakdown or infection.
Long term patency rates are so much superior with arterial grafts that new procedures are continually under development.
The gastro-epiploic artery can be brought up through the diaphragm to arteries on the inferior surface of the heart and the epigastric artery can be dissected from the anterior abdominal wall and used as a “free” graft in place of saphenous veins.
Some histological changes are seen in most vessels used as bypass grafts.
Reversed saphenous grafts develop fibrous intimal thickening.
In some lipid accumulation, hemorrhage and necrosis produces a picture, which is very similar to atherosclerosis.
Grafts dilate in the weeks or months after surgery and this has an anti-occlusive effect.
Internal mammary grafts have a greater long term patency rate.
Prosthetic vessels used in peripheral artery surgery develop a “pseudointima” of fibrin and platelets but never acquire a full endothelial lining.
The fabric wall excites a foreign body inflammatory reaction and fibrosis binds the external wall to the surrounding connective and muscular tissues.
Other cardiac procedures:
If a prosthetic valve has been inserted, a single transverse cut above the base will usually display part of the aortic, the mitral and tricuspid valves.
The most important complications of valve replacement are infective endocarditis and perivalvular leaks.
Homografted valves are liable to structural failure and may calcify, especially in children.
Postmortem clot commonly forms around prosthetic valves and must be carefully removed to expose true thrombus or dehiscence around the valve annulus.
In some patients who are not fit for an open valve replacement balloon valvuloplasty may allow at least a temporary increase in cardiac output.
Some degree of damage to the calcified cusps is inevitable and debris may embolize into the systemic circulation.
Postoperative arrhythmias are commonest but their cause is often uncertain.
A few patients with previously normal atrial function, who undergo thoracic surgery, develop fibrillation postoperatively.
Increasing age and obesity are important predisposing factors.
The leading non-cardiac complication occurring after open heart surgery is infection.
Major problems are wound infection, urinary tract and respiratory infection.
Sternal and mediastinal infections are particular difficult to manage.
Although post operative infections are a major cause of prolonged patient stay in the hospital they are rarely directly responsible for death.
There is a low but significant incidence of neurological and neuropsychiatric abnormalities after bypass procedures. Most are transient and the risk of permanent neurological damage is very rare.
Angioplasty and atherectomy:
Percutaneous transluminal coronary angioplasty (PTCA) involves the balloon dilatation of stenotic segments of major coronary arteries or occasionally coronary artery bypass grafts which have become chronically occluded.
When the technique was first developed, it was though that the patency was restored by simple compression of the atheromatous lesion.
It is now clear from both clinical and experimental studies that tears and splits are produced around the edges of atheromatous plaques which then allow stretching of the underlying muscular media.
Sometimes these tears extend in to the media producing a “coronary dissection”.
A minor degree of dissection is common after angioplasty, but if this is too extensive the vessel may rupture.
Acute complications of angioplasty include thrombus formation, pericarditis, acute adventitial inflammation and distal embolization of atheromatous debris.
Restenosis occurs in some cases. In most centers the immediate mortality associated with PTCA is now less than 1%, but a few of the patients develop an acute myocardial infarction and some of these patients require an emergency coronary artery bypass graft.
Directional coronary atherectomy is used to excise atheromatous debris from arteries, rather than simply compressing and rupturing plaques.
The procedure causes more physical damage to the vessel wall and has a higher instance of wall rupture.
The debris extracted may be submitted for histological examination.
All forms of cardiac catheterization carry a risk of coronary artery dissection.
In all deaths after cardiac catheterization it is advisable to consult with the responsible cardiologist and review the angiographic films before selecting coronary arterial segments for histology.
The major coronary artery branches are usually visible on angiograms and these help to localize the precise site at which the procedure was undertaken.
Some arrhythmias are now treated by percutaneous catheter ablation techniques.
Precise identification of the site of the therapeutic injury is necessary.
Significant value of autopsy for quality management in cardiac surgery.
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