Figure 11-1 Thoracic radiographs from a dog with pericardial effusion. A, The lateral projection shows a markedly enlarged cardiac silhouette, tracheal elevation, and overlap of the cardiac silhouette and diaphragm. B, The ventrodorsal projection shows bilateral contact between the pericardial sac and the costal margins. The edge of the cardiac silhouette is sharply delineated, and the lung fields are clear of any infiltrate that would indicate the presence of left-sided congestive heart failure.

Electrocardiography

• Most dogs with pericardial effusions have either a normal sinus rhythm or a sinus tachycardia.

• Ventricular arrhythmias are fairly common and supraventricular arrhythmias occasionally occur.

• Low voltage QRS complexes (R waves < 1 mV in all limb leads) are present in approximately half of the cases (Figure 11-2, A, B).

• Electrical alternans, a beat-to-beat variation in the contour and amplitude of the QRS and ST-T complexes (Figure 11-2, C), is strongly suggestive of a pericardial effusion. Electrical alternans is present in up to approximately 20% of dogs with pericardial effusions.

Figure 11-2 Electrocardiograms (lead II) from dogs with pericardial effusion. Calibration square wave is 1mV in amplitude. A, Before pericardiocentesis, the complexes are low voltage (R wave < 1 mV) and heart rate is 140 beats per minute (bpm). B, After pericardiocentesis, R wave amplitude is almost 2 mV and heart rate is 100 bpm. C, Beat-to-beat variations in amplitude and contour of the QRS and ST-T complexes that characterize electrical alternans.

(Modified from Tobias AH: Pericardial disorders. In Ettinger SJ, Feldman EC, eds: Textbook of veterinary internal medicine, ed 6, St Louis, 2005, WB Saunders.)

Pericardial Fluid Analysis

• Pericardial effusions in dogs irrespective of cause are virtually always sanguinous or serosanguinous sterile inflammatory exudates.

• Total nucleated cell counts, red cell counts, protein concentrations and pericardial fluid pH overlap extensively between the various neoplastic and non-neoplastic causes.

• Hemangiosarcoma and aortic body tumors, the most common tumors associated with pericardial effusions in dogs, are rarely identified on cytologic evaluation of pericardial fluid. Also, pericardial diseases that lead to effusion result in dramatic mesothelial proliferation, and exfoliated mesothelial cells often have characteristics that mimic malignancy. Cytology must be interpreted very cautiously.

• However, some of the less common causes of pericardial effusion, such as infectious pericarditis and lymphosarcoma, are diagnosed primarily on the basis of pericardial fluid cytology. Consequently, the authors submit pericardial fluid for analysis in all cases with pericardial effusions, despite the generally low diagnostic yield of this test.

Key Point

Cytologic examination of pericardial effusates is unreliable in distinguishing neoplastic vs. non-neoplastic (i.e., inflammatory) etiologies in the large majority of cases of pericardial effusion in the dog.

Echocardiography

• Echocardiography is the most sensitive and specific noninvasive method to confirm the presence of pericardial effusion.

• With two-dimensional echocardiography, pericardial effusion appears as an anechoic space surrounding the heart. In cases with concurrent pleural effusion, the pericardium is well visualized with anechoic fluid on either side.

• The heart may show swinging motions within the pericardial fluid.

• The various heart chambers may appear small and the walls may show thickening or pseudohypertrophy due to external compression.

• The right atrial free wall is normally rounded throughout the cardiac cycle, reflecting the normal positive right atrial transmural pressure. Any inversion or collapse of the right atrial free wall provides indirect evidence of elevated intrapericardial pressure and transient reversal of transmural pressure (echocardiographic evidence of cardiac tamponade). Right atrial inversion occurs in late diastole and continues into ventricular systole for a variable period before normalizing (Figure 11-3, A).

• Cardiac tamponade leading to right ventricular diastolic collapse is characterized by inward motion of the right ventricular free wall (Figure 11-3, B). This may range from transient and localized concavity of the right ventricular free wall, to virtual complete right ventricular chamber obliteration throughout diastole.

• In addition to confirming the presence of pericardial effusion and cardiac tamponade, echocardiography is the noninvasive procedure of choice to detect associated intrapericardial masses such as hemangiosarcoma and heart base tumors. Whereas histopathology is necessary to confirm and definitively identify a tumor, the echocardiographic location and characteristics of an intrapericardial or myocardial mass provides important information about the probable tumor type.

• The following echocardiographic features are consistent with a diagnosis of hemangiosarcoma:

• Hemangiosarcoma most commonly arises from the wall of the right atrium or auricle, protrudes into the pericardial space, and moves with the right auricle or atrium (Figure 11-4).

• These tumors may also protrude into the right atrial chamber, spread to involve other areas of the heart base and pericardium, and involve the right atrioventricular groove (see Figure 11-3, A).

• Hemangiosarcoma typically contains small hypoechoic spaces, giving the tumor a mottled or cavitary appearance, and the tumors are occasionally cystic (see Figure 11-4).

• Hemangiosarcoma, when present, is usually demonstrated while imaging from the right parasternal long- and short-axis views. However, these tumors may be small and elusive. Imaging from the left parasternal locations to provide alternate imaging planes, especially of the right auricle, is necessary to demonstrate the presence of hemangiosarcoma in some cases.

• Hemangiosarcoma involving the wall of the left ventricle has been described.

• The following echocardiographic features are characteristic for heart base tumors:

• Heart base tumors are usually associated with the ascending aorta (Figure 11-5, A).

• They vary from small ovoid structures attached to the ascending aorta, to very extensive masses that surround the aorta and main pulmonary artery.

• Tumor indentation or invasion of the atria and major blood vessels may be seen (Figure 11-5, B).

• Heart base tumors tend to have a more homogenous appearance than the mottled or cavitary appearance of hemangiosarcoma.

• Heart base tumors are usually, but not invariably, associated with pericardial effusions.

• Echocardiography may also demonstrate:

• Cardiac tumors other than hemangiosarcoma and heart base tumors.

• The presence of abdominal viscera within the pericardial sac in cases with peritoneopericardial diaphragmatic hernia.

• Benign intrapericardial cyst.

• Intrapericardial thrombi associated with left atrial perforation. Left atrial perforation is suspected when signs of acute tamponade develop in smaller breed dogs with significant mitral regurgitation.

Figure 11-3 Echocardiographic tamponade in a dog with pericardial effusion (PE). The images were recorded from the right parasternal location. A, Late diastolic inversion of the right atrium (arrow). The mass at the atrioventricular groove was confirmed as hemangiosarcoma by surgical biopsy. B, Diastolic inversion of the right ventricular wall (arrow). RV, Right ventricle.

Figure 11-4 Echocardiographic images from a dog with cardiac hemangiosarcoma recorded in the short-axis view from the right parasternal location. A, A cavitary and cystic mass (arrow) is associated with the right auricle (RA). B and C, The mass moves back and forth with right auricular motion during different phases of the cardiac cycle. AO, Aorta; PE, pericardial effusion.

Figure 11-5 Echocardiographic images from a dog with a heart base tumor recorded from the left cranial parasternal location. A, A large homogeneous mass (arrow) is attached to the caudal aspect of the aorta (AO). B, The tumor has infiltrated the main pulmonary artery (PA). LVOT, Left ventricular outflow tract; LA, left atrium.

Initial Patient Stabilization: Pericardiocentesis

• Pericardiocentesis to remove as much pericardial fluid as possible is necessary for initial patient stabilization in any case with a pericardial effusion that is causing significant hemodynamic compromise (clinical cardiac tamponade).

Key Point

The presence of pericardial fluid greatly facilitates the detection of intrapericardial masses, and this is particularly relevant to the diagnosis and delineation of hemangiosarcoma and heart base tumors. Pericardial fluid forms an echolucent zone around the right atrium and auricle and the ascending aorta, the locations at which these tumors most commonly occur. In the absence of pericardial fluid, these locations are obscured by lung interference. Consequently, whenever the clinical condition of the patient permits, pericardiocentesis should be deferred until a thorough echocardiographic examination has been completed.

• The authors’ preferred approach is to restrain the animal in left lateral recumbency and to approach the pericardium from the right side. This reduces the risk of lacerating a coronary blood vessel during the procedure.

• Dogs usually tolerate the procedure without sedation, but mild sedation is necessary in some cases.

• The authors usually use a 14- or 16-gauge over-the-needle catheter system to perform pericardiocentesis in dogs. Two small side holes are made near the tip of the catheter to avoid any blockages and aspirating the myocardium against a single end hole during the procedure.

• The catheter system is coupled to a large volume syringe via an extension tube and a three-way stopcock.

• The right thorax is shaved and the ideal location to perform the procedure is determined by echocardiography. The location is selected to avoid lung and to approach the pericardium perpendicularly with the catheter system. This usually coincides with the fifth or sixth intercostal space at about the level of the costochondral junction.

• The skin, intercostal muscles, and parietal pleura are infiltrated with local anesthetic, and the area is surgically prepared.

• A small skin incision is made (Figure 11-6, A) and the catheter system is advanced towards the pericardium (Figure 11-6, B).

• Slight negative pressure is applied and maintained via the syringe and extension tube as the catheter system is advanced.

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