SPOTLIGHT ON PERICARDIAL DISEASE

Transcription

1 Vet Times The website for the veterinary profession SPOTLIGHT ON PERICARDIAL DISEASE Author : DAN FORSTER Categories : Vets Date : February 16, 2009 DAN FORSTER discusses the spectrum of disorders under this clinical umbrella and emphasises the value of a full investigation in light of variable prognoses PERICARDIAL diseases comprise a small proportion of clinically important cardiovascular diseases in dogs and cats (estimated at one per cent). Although significantly less common than valvular, congenital or myocardial heart disease, pericardial disease is regarded as one of the most common causes of right-sided congestive heart failure in dogs. However, pericardial disease is rare in cats. Congenital or acquired Congenital pericardial disorders: - peritoneal-pericardial diaphragmatic hernia (PPDH); - pericardial defects; and - pericardial cysts. Acquired pericardial disorders: - pericardial neoplasia; 1 / 14

2 - constrictive pericarditis; and - pericardial effusion. Anatomy The heart and great vessels are enveloped in the pericardial sac, which is composed of two layers: a tough outer fibroserous membrane (parietal pericardium) and a delicate inner serous membrane (visceral pericardium). A pericardial cavity is formed between the two layers; normal cats and dogs have approximately 0.25ml/kg of pericardial fluid in this cavity. The blood supply is from the pericardial branches of the aorta, internal thoracic and musculophrenic arteries. Innervation is from the vagus nerve, left recurrent pharyngeal nerve, and oesophageal plexus. There is also a rich sympathetic nerve supply from stellate and first dorsal root ganglions. The phrenic nerve may also supply sensory fibres to the pericardium. Function The pericardium is very distensible when first filled and non-distensible when full. An increase in volume leads to hypertrophy and this serves to increase reserve volume and compliance. The true physiological role of the pericardium remains controversial, but various theories have been postulated. It is not essential for normal cardiovascular function and adverse effects are not associated with surgical removal. The pericardium helps protect the heart from adjacent infection and malignancy, and also functions to anchor the heart in position within the chest. The pericardium is continuous with the greater vessels at the heart base and the sternopericardiac ligament at the apex. Pericardial fluid may help reduce friction generated by the beating heart and may also help to prevent overdistention. Peritoneal-pericardial diaphragmatic hernia This uncommon congenital defect causes a persistent communication between the pericardial and peritoneal cavities, allowing abdominal contents to enter the pericardial sac. The liver and gall bladder are the most common organs to herniate. Associated abdominal wall hernias and sternebrae abnormalities may occur. Some studies suggest a predisposition among males and Weimaraners. Clinical signs are not always obvious from a young age. Patients may initially present with respiratory or gastrointestinal signs. An associated pericardial effusion is unusual, but this has 2 / 14

3 been reported; surgical correction carries a good prognosis. Pericardial neoplasia The most commonly reported cardiac tumours are haemangiosarcomas, originating in the right atrial wall or atrial appendage, and heart-base tumours (chemodectoma or aortic body tumour). Ectopic thyroid carcinomas and mesotheliomas are less common. Metastatic carcinoma to the heart may also occur. Tumours of the pericardium are not usually exfoliative, so echocardiography of the heart entirety is important to rule out neoplasia when pericardial effusion is present. Neoplasia is reportedly the most common cause of pericardial effusion in dogs. Lymphosarcoma, mesothelioma and metastatic carcinoma have been reported in cats. Haemangiosarcomas are particularly common in German shepherd dogs and may be associated with metastases (such as in the kidney, liver, spleen or lungs see Figure 1 ) as well as systemic illness and arrhythmias. Pericardial effusion Most diseases that affect the pericardium result in pericardial effusion. Effusions can be transudative, exudative (inflammatory), or sanguineous. Causes of pericardial transudation include right-sided congestive heart failure and hypoproteinaemia. Transudative pericardial effusions are usually subclinical. Infectious pericarditis is an uncommon cause of pericardial effusion in small animals and usually causes a fibrinous exudate. Various bacterial and fungal organisms have been associated with such infections for example, bacterial pericarditis may be associated with bite wounds or migrating foreign bodies, whereas coccidiomycosis is an important cause of effusions in endemic regions. In cats, feline infectious peritonitis and toxoplasmosis are potential causes of inflammatory effusions. Idiopathic (benign) pericardial effusion is regarded as the second most common cause of pericardial effusion in dogs. The effusion is usually sanguineous and must be differentiated from neoplastic effusion. The presence of blood in the effusion is more suggestive of atrial rupture, which can occur secondary to chronic mitral insufficiency. Large-breed dogs are most commonly affected, with both neoplastic and idiopathic effusions. The majority of pericardial effusions are sanguineous and port wine in colour. Acute or chronic 3 / 14

4 Pericardial effusion may develop relatively slowly or rapidly. As fluid collects, the filling ability (diastolic function) is impeded. The right side of the heart suffers more than the left. With rapid (acute) filling, right heart dysfunction also occurs rapidly. With gradual accumulation, the pericardium can stretch to accommodate a greater volume of fluid with less cardiac impairment. Cardiac tamponade is the term given for an impairment of ventricular filling as a consequence of increased intrapericardial pressure caused by the accumulation of fluid within the pericardial cavity. As pericardial fluid accumulates, more pressure is needed to push blood into the right and left ventricles during diastole to maintain cardiac output. As intrapericardial pressure continues to increase, cardiac output decreases and systemic venous pressure increases. Gradual rises in pressure often lead to signs of systemic congestion (such as ascites and pleural effusion), whereas acute increases in pressure may lead to the development of cardiac shock before signs of systemic congestion are evident. Diagnosis Clinical signs depend on the rate of rise of intrapericardial pressures. Typical signs are weakness, exercise intolerance and dyspnoea. Muffled heart sounds, jugular venous distension and weakened arterial pulses in combination are suggestive of pericardial effusion. Signs of rightsided heart failure (for example, ascites) may also be present. Echocardiography Echocardiography is the quickest and safest method of diagnosing the condition. The pericardial fluid will appear as an anechoic space between the epicardium and pericardium. The approximate volume of the effusion can also be appreciated, although the pressure within the pericardial sac is more important. The entirety of the heart should be checked to rule out neoplasia as a cause. The location of any masses is useful to help establish what type of tumour is present (see earlier). Electrocardiography Electrocardiography may also show some typical features of pericardial effusion. Features may include low-amplitude QRS complexes, sinus tachycardia, ventricular premature beats and possibly electrical alternans ( Figure 2 ). This is created by a beatto-beat variation in amplitude of QRS complexes as the heart swings within the fluid-filled sac. Radiology 4 / 14

5 Radiology is useful, but care should be taken in restraint and the use of sedation is not recommended or necessary. A large globose heart is typical, with well-defined borders of the cardiac silhouette ( Figure 3 ). Concurrent pleural effusion and metastases are possible. Distension of the caudal vena cava, ascites ( Figure 4 ) and hepatomegaly are more common features in chronic effusions. Further tests - Cytology. Studies indicate that cytology is of little value in distinguishing between idiopathic and neoplastic aetiologies. - Biochemistry. The ph of fluid may help: ph of less than seven has been linked to an inflam matory aetiology, while ph of more than seven suggests a nonneoplastic aetiology. - Bacterial culture. This is useful in infectious effusions. Treatment Pericardiocentesis This allows rapid control, especially if cardiac tamponade has developed. See the next section for the technique involved. Corticosteroids These have been suggested in some studies to help prevent recurrence in idiopathic cases. Pericardectomy This procedure involves surgical removal of the pericardial sac via thoracoscopy or thoracotomy. Percutaneous balloon pericardiotomy This may be a useful palliative treatment of recurrent pericardial effusion. Note that diuretics are contraindicated as they can further reduce the blood pressure and increase the risk of cardiocirculatory collapse. Pericardiocentesis technique Animals with pericardial effusion have poor venous driving pressure, so intravenous fluids are useful to aid venous return. Animals should have an ECG during the procedure so changes can be 5 / 14

6 monitored for example, if the myocardium is pierced. Some patients may allow the procedure to be performed conscious and light sedation may be necessary in others. The approach can be from the left or right there are arguments for and against both approaches and sternal or lateral recumbency can be used. A 14-gauge to 18-gauge needle or catheter is useful for the procedure. From the right side an area between the third to eighth ribs should be clipped from the sternum to above the costochondral junction. The puncture site should be based on thoracic radiographs (most commonly between the fourth and fifth intercostal spaces). The area can be injected with 1-2ml of local anaesthetic and five minutes should be allowed for the block to take effect. The catheter should be inserted at a right angle to the skin for 1.5 inches. The angle is then changed to a cranioventral angle towards the downside shoulder. The lung parenchyma is above this angle of entry so damage to lungs should not be an issue. Ultrasound guided centesis may be helpful with smaller effusions. When fluid is obtained it is typically port wine coloured ( Figure 5 ) and at low pressure. Brighter or higher-pressure fluid may indicate heart blood. Effusion fluid should not clot so PCV can be checked to ensure fluid obtained is not blood. When fluid is obtained, the needle can be removed and the three-way tap can be attached. Pericardiocentesis is not risk free; coronary artery laceration is possible and can result in sudden death. The ECG will help ascertain if myocardial contact has occurred. Ventricular arrhythmias may occur if the heart surface is touched, but these are likely to subside quickly if the needle is withdrawn slightly. Constrictive pericarditis This occurs when pericardial disease is characterised by fibrosis of the pericardium (usually only the parietal pericardium). Often there is no associated effusion. The fibrosis causes a restriction to the filling of the right ventricle (like pericardial effusion). This condition may be a result of recurrent effusions, foreign bodies, infection or neoplasia. Presenting signs are the same as for pericardial effusion, and mainly middle-aged, large-breed dogs are affected. On radiography there is absence of a globose heart and variable amounts of effusion. Caudal vena cava enlargement and mild to moderate cardiomegaly may occur. Even with echocardiography, detection of a thickened pericardium can be difficult. Definitive diagnosis is hard. Cardiac catheterisation will demonstrate elevation of pressures, and surgical demonstration of fibrosis at parietal pericardectomy will often be necessary to confirm the diagnosis. Response to surgery is usually excellent. 6 / 14

7 Conclusion The prognosis of pericardial disease depends on the initial condition. For example, the most commonly encountered pericardial conditions are neoplastic and idiopathic pericardial effusion. These carry poor and good prognoses respectively, so it is important to investigate the disease fully before treatment options are discussed with owners of afflicted patients. References Atkins C E et al (1993). Intrapericardial cysts in the dog, Journal of Veterinary Internal Medicine 7: Berg R J and Wingfield W (1984). Pericardial effusion in the dog: a review of 42 cases, Journal of the American Animal Hospital Association 20: Brownlie S E and Cobb M A (1992). Intrapericardial neoplasia in 14 dogs, Journal of Small Animal Practice 37: Edwards N J (1996). The diagnostic value of pericardial fluid ph determination, Journal of the American Hospital Association 32: Ettinger S J and Feldman A C (2000). Pericardial disorders. In: Textbook of Veterinary Internal Medicine: Diseases of the Dog and Cat (4th edn), W B Saunders: 1,132-1,150. Dunning D et al (1998). Analysis of prognostic indicators for dogs with pericardial effusion: 46 cases ( ), Journal of the American Veterinary Medical Association 212: 1276 Hopper D L and Ware W A (1999). Cardiac tumours in dogs: , Journal of Veterinary Internal Medicine 13: / 14

8 Figure 1. Lung metastases as well as those in the kidney, liver or spleen may be associated with pericardial neoplasia. 8 / 14

9 Figure 2. Electrical alternans may be seen in pericardial effusion as the heart swings within the pericardial sac. 9 / 14

10 Figure 3 (above). An enlarged, very rounded heart with distinct borders is typical of pericardial effusion, although echocardiography is preferable for definitive diagnosis. 10 / 14

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13 Figure 4 (left). Ascites may be seen in right sided heart failure associated with pericardial effusions. 13 / 14

14 Powered by TCPDF ( Figure 5. Pericardial effusions are usually port wine coloured. 14 / 14