Pericardial disease: The forgotten cardiac malady

Diseases primarily affecting the pericardium account for approximately 5% of all patients with cardiovascular disease.¹ Although primary pericardial disease represents a small percentage of the total number of cardiac diseases in small animals, it is an important cause of right heart failure in dogs. Primary pericardial disease in cats is uncommon; most frequently representing a sequelae of primary myocardial disease. Several types of primary and secondary pericardial diseases occur, the most common of which are those resulting in pericardial effusion.

Congenital diseases

There are several congenital diseases of the pericardium recognized in small animals. Although peritoneopericardial diaphragmatic hernias (PPDH) are the most common type of congenital abnormality encountered (Figure 1), sporadic reports of partial pericardial defects and intrapericardial cysts have been published.²

Figure 1: Lateral and ventrodorsal radiographs of a cat with a peritoneal pericardial diaphragmatic hernia (PPDH). Notice the irregularity of the cardiac silhouette as well as the variable density within the pericardial shadow consistent with omental and hepatic herniation.(All images courtesy of Miller)

Acquired pericardial diseases

Pericardial effusion

Diseases causing pericardial effusion are the most common causes of clinically significant pericardial disease in dogs. Idiopathic intra-pericardial hemorrhage and neoplasia of the heart, heart base, or pericardium are the most common causes of hemorrhagic effusion in this species.³ Clinically important tumor types in dogs include hemangiosarcoma of the right atrium, commonly seen in golden retrievers and historically in German shepherd dogs. Aortic body tumors (chemodectoma, nonchromaffin paraganglioma) with invasion of the heart base are most seen in aged brachycephalic breeds such as Boston terriers and boxers. Less common tumor types include ectopic (heart base) thyroid carcinoma, mesothelioma, and metastatic carcinoma. A well-recognized but uncommon cause of intrapericardial hemorrhage in small breed dogs is left atrial tear secondary to severe chronic endocardiosis of the mitral valve. Infectious causes of pericardial effusion including coccidioidomycosis are uncommon but represent an important cause of pericardial disease in endemic regions.

Diagnosis

Special breed predilections have been noted above and most frequently, animals with pericardial disease are presented with vague signs. Clients will frequently describe lethargy, exercise intolerance, and anorexia. Occasionally, patients with more advanced disease will be presented for signs of right heart failure including abdominal distension, respiratory difficulty, or syncope.

Signs of elevated right heart pressures are consistently present in patients with clinically significant pericardial disease. Jugular venous distention (Figure 2) or positive hepatojugular reflux are invariably present, but commonly overlooked. Heart sound intensity is frequently diminished. Lung sounds may be diminished if pleural effusion is present. Other auscultatory abnormalities (gallop rhythms, cardiac murmurs, arrhythmias) are very uncommon. Dogs with left atrial tears secondary to chronic degenerative valvular disease will have a systolic murmur that may decrease in intensity when compared to previous examinations. Hepatomegaly and free abdominal fluid may be found. If the disease is chronic, significant weight loss may be observed.

Figure 2: Jugular venous distention in a dog with a chemodectoma, large volume pericardial effusion, and resultant cardiac tamponade.

Thoracic radiography usually demonstrates abnormalities when there is significant accumulation of pericardial fluid. The cardiac silhouette loses its angles and waists and becomes globe-shaped (Figure 3). Most cases are not "classic" and require integration with the other data. Pulmonary vascularity is often reduced from low cardiac output in contrast to congestive heart failure (CHF) from cardiomyopathy or valvular disease in which the pulmonary vascularity may be increased (especially the pulmonary veins).

Figure 3: Lateral and ventrodorsal radiographs of a dog with large volumetric pericardial effusion. Note the lack of specific chamber enlargement patterns. The sheer degree of enlargement of the cardiac silhouette should raise the suspicion of pericardial effusion.

Electrical alternans is a beat-to-beat voltage variation of the QRS or ST-T complexes (Figure 4). It may be recorded in as many as 50% of patients with pericardial effusion. Elevation of the ST segment is commonly recorded in patients with pericardial disease. Reductions in QRS voltage (R < 1 mV in Lead II) are commonly recorded in dogs with pericardial effusion. In the author's experience, arrhythmias other than sinus tachycardia are uncommon in primary pericardial disease.⁴

Figure 4: Lead II electrocardiogram showing atrial tachycardia with an average heart rate of 180 bpm. Additionally, the 1:1 variation in R-wave amplitude is consistent with a diagnosis of electrical alternations, a common finding in patients with large volume pericardial effusion.

Echocardiography is the most sensitive and specific non-invasive method of detecting pericardial effusion currently available (Figure 5). The hemodynamic consequences of pericardial effusion depend not only on the amount of pericardial effusion present but also the rapidity with which the effusion has accumulated. A small or moderate amount of fluid that accumulates rapidly (left atrial rupture) may produce significant hemodynamic compromise, while a large effusion that accumulates over months may have little hemodynamic effect.

Figure 5: Right parasternal short axis view obtained at the level of the mitral papillary muscles. A large anechoic separation is noted between the epicardium and the pericardium characteristic of pericardial effusion.

Therapy and prognosis

Pericardiocentesis

Pericardiocentesis is the treatment of choice for initial stabilization of dogs and cats with pericardial effusion and cardiac tamponade. When performed properly, pericardiocentesis is associated with minimal complications. Before performing pericardiocentesis, it is necessary to shave and surgically prepare a large area of the right hemithorax (sternum to mid thorax, third to eighth rib). Local anesthesia is sometimes adequate; however, mild sedation is frequently necessary. It is important to ensure that the pleura has been infiltrated, as pleural penetration seems to cause significant discomfort. The patient is placed in sternal or lateral recumbency, depending on demeanor (Figure 6). Occasionally, pericardiocentesis can be accomplished in the standing animal, but adequate restraint is essential to prevent cardiac puncture or pulmonary laceration. Electrocardiographic monitoring during the procedure is helpful since epicardial contact often causes ventricular arrhythmias.

The puncture site is usually determined based on the location of the heart on thoracic radiographs. This is most commonly between the fourth and sixth rib spaces at the costo­chondral junction. Ultrasound guidance is infrequently necessary unless the volume of effusion is very small, or the effusion is compartmentalized.

The size of the needle or catheter used is dependent on the size of the animal. In cats, a 19-to-21-gauge butterfly catheter is typically appropriate. In large dogs, a 14- or 16-gauge over-the-needle catheter is used (Figure 7).

The needle or catheter should be attached to a 3-way stopcock, extension tubing, and a syringe to allow constant negative pressure to be applied during insertion and drainage. Care should be taken to avoid the large vessels that run along the caudal border of the ribs.

Once the catheter has been inserted through the skin, negative pressure should be applied. If pleural effusion is present, it will be obtained immediately upon entering the thoracic cavity. It is most commonly a clear to pale yellow color. As the catheter is advanced and contacts the pericardium, a scratching sensation will be noticed. Minimal advancement will result in penetration of the pericardium.

Figure 6: Patient positioned in sternal incumbency with a large area both clipped and prepped for sterile puncture using a large over-the needle catheter.

Figure 7: Basic supplies used for pericardiocentesis.

Most pericardial effusions are hemorrhagic and have a "port wine" appearance (Figure 8). Once effusion of this character is obtained, the catheter should be advanced over the needle, and the needle removed. The remainder of the drainage should be performed using the catheter. Advancing the needle too far will result in contact with the epicardium. This is often felt as a tapping or more intense scratching sensation and commonly results in ventricular arrhythmias. These arrhythmias are usually self-limiting following retraction of the needle or catheter.

Figure 8: Characteristic “port wine” appearance of pericardial effusion. Although the fluid appears very hemorrhagic, the PCV is approximately 10% arguing against acute hemorrhage or cardiac perforation.

Potential complications include cardiac puncture (with resultant hemorrhage or arrhythmias), coronary artery laceration, lung puncture or laceration, and dissemination of infection or neoplasia throughout the thoracic cavity. Diagnostic evaluations of fluid obtained should include PCV and cytologic evaluation. Bacterial culture and sensitivity should be performed if indicated by cytologic evaluation. Caution should be exercised when evaluating the cellular component of pericardial effusion. Clinically important neoplasia of the heart and pericardium (hemangiosarcoma, chemodectoma) commonly do not exfoliate, resulting in frequent false negative evaluations. Reactive mesothelial cells within the pericardial sac are commonly over-interpreted as being neoplastic, causing false positive results (Figure 9).

Figure 9: Cytologic sample from a patient with confirmed idiopathic hemorrhagic pericardial effusion. The cytologic characteristics of the intrapericardial mesothelial cells can be incorrectly interpreted as representing neoplasia

The long-term prognosis for dogs with hemorrhagic effusion is dependent on the underlying etiology. With idiopathic hemorrhagic pericardial effusion, a single pericardiocentesis is curative in approximately 50% of the cases.⁵ In the remainder, repeat pericardiocentesis may be necessary to control clinical signs. Fluid may reaccumulate rapidly (within several days) or may not recur for months to years. In patients requiring more than 2 taps, the author recommends subtotal pericardiectomy. Following the initial pericardial tap, administration of oral prednisolone (starting at a dose of 1 mg/kg orally every 12 hours, then gradually tapering off over a two-to-three-week period) may be beneficial. Although anti-inflammatory doses of prednisolone are commonly administered to dogs with idiopathic pericardial effusion, there are no controlled studies to confirm the efficacy of this therapy. Subtotal pericardiectomy is usually curative in dogs with idiopathic pericardial effusion.

If cardiac or pericardial neoplasia is the cause of the pericardial effusion, the recommended therapy is influenced by the suspected tumor type. Aortic body tumors are commonly associated with slow growth and are late to metastasize. Subtotal pericardiectomy may afford palliation for up to three years. Recent studies have suggested that stereotactic radiation therapy radiation therapy coupled with Paladia may further improve survival.⁶ Hemangiosarcoma of the right atrium is associated with a poor long-term prognosis and pericardectomy is not recommended in these cases. Additionally, most hemangiosarcomas involving the right atrium or right ventricle are not amenable to surgical removal. The tumor has commonly spread to the lungs at the time of diagnosis and a small number of these patients may also have neoplastic lesions in the spleen or liver at the time of initial diagnosis.

Matthew W. Miller, DVM, MS, DACVIM (Cardiology) earned both a Doctor of Veterinary Medicine and Master of Science degree from The Ohio State University. He completed a small animal medicine and surgery internship at the West Los Angeles Veterinary Medical Group and a cardiology residency at The Ohio State University. He is a diplomate of the American College of Veterinary Internal Medicine (Cardiology). Miller has served as a faculty member at Texas A&M University’s College of Veterinary Medicine and Biomedical Sciences where he achieved the position of full professor with tenure. He is currently the founding medical director and a staff cardiologist at the Animal Medical and Surgical Center in Scottsdale, Arizona, and Thrive Pet Healthcare’s National Specialty Director of Cardiology.

References

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