The pericardium
This is a fibrous envelope covering the heart and separating the heart from the mediastinal structures. It is a fibrous structure with a parietal layer and it allows the heart to move with each beat. It is not essential for life because it can be left wide open after cardiac surgery without any ill effects. There is, however, a number of conditions affecting the pencardium which may present to the surgeon.
Pericardial effusion
There is a continuous production and resorption of pericardial fluid. This is a balanced system and only a few millilitres of fluid are present at any one time. A disease process that disturbs this balance by increasing production or interfering with resorption will lead to a build-up of fluid in the pericardium. If the pressure exceeds the pressure in the atria, compression will occur, venous return will fall and the circulation is compromised. This state of affairs is called tamponade. A gradual build-up of fluid (e.g. malignant infiltration) may be well tolerated for a long period before tamponade occurs, and the pericardial cavity may contain 2 litres of fluid. Acute tamponade (penetrating wounds or postoperatively) may occur in minutes with small volumes of blood. The clinical features are low blood pressure with a raised jugular venous pressure (JVP) and pulsus paradox. Kussmaul's sign is a characteristic pattern when the JVP rises with inspiration as a result of the impaired venous return to the heart.
Emergency treatment of pericardial tamponade is aspiration of the penicardial space and therefore relief of the compression on the cardiac chambers. A wide-bore needle is inserted under local anaesthesia to the left of the xiphisternum between the angle of the xiphisternum and the ribcage (Fig. 48.58). The needle is advanced towards the tip of the scapula into the pericardial space. An EGG electrode attached to the needle will indicate when the heart has been touched.
This will hold the situation temporarily until the cause of the tamponade is established. It is occasionally possible to drain the pericardium with a percutaneous drainage system. To prevent recurrence of a chronic tamponade, it is sometimes necessary to fashion a pericardial window between the pericardial space and the pleural or peritoneal space. This may be done through a subxiphoid incision, anterolateral thoracotomy, either thoracoscopically or percutaneously. Penetrating wounds of the heart usually require exploration
through a median sternotomy. Emergency room thoracotomy is rarely required.
Causes of acute tam ponade
The causes include:
· trauma;
· aortic dissection;
· penetrating cardiac injury (usually of the atnia as ventricular and aortic wounds tend to be fatal);
· iatrogenic: penetration of the right ventricle following central venous cannulation, endomyocardial biopsy, etc.;
· postoperative: blocked drains or inability of the drains to cope with excessive blood loss.
Chronic tamponade is usually a result of malignant infiltration of the penicardium (usually secondary carcinoma from breast or bronchus) or very occasionally uraemia or connective tissue diseases.
Pericarditis
Infection and inflammation may also affect the penicardium. Acute penicarditis usually occurs following a viral illness. There is a sensation of heaviness in the chest which may be positional. Treatment is with nonsteroidal anti-inflammatory drugs and bed rest (in case there is an underlying myocarditis). Acute purulent penicarditis is uncommon but requires urgent drainage and intravenous antibiotics with attention to the underlying cause.
Chronic penicarditis is an uncommon condition in which the penicardium becomes thickened and noncompliant. The heart cannot move freely and the stroke volume is reduced by the constrictive process. The central venous pressure is raised and the liver becomes congested. Peripheral oedema and ascites are also a feature. Establishing the diagnosis may not be easy because the chest radiograph and echoradiograph may be normal. Cardiac cathetenisation demonstrates a reversed square root sign'. Treatment is aimed at relieving the constriction. The heart is approached through a median sternotomy and the penicardium is carefully stripped off the left ventricle, followed by the right ventricle. Cardiopulmonary bypass may be required if haemodynamic instability occurs.