33 Gilles Dupre Pericardial effusion is present in approximately 7% of dogs with clinical signs of cardiac disease.1 The most common causes of pericardial effusion in dogs are idiopathic pericarditis and neoplasia.2-4 In cats, pericardial effusion is often associated with feline cardiomyopathy, feline infectious peritonitis, and neoplasia (primarily lymphosarcoma). Idiopathic pericardial effusion refers to sterile, often hemorrhagic effusion in the pericardial space with no evidence of neoplasia, cardiac disease, trauma, or infection. German shepherd dogs, golden retrievers, Great Danes, and Saint Bernards appear to be predisposed. The age at presentation ranges from 1 to 14 years with a mean of 6 years. Male dogs appear to be affected more frequently than female dogs.5 Histologic examination of tissue specimens from dogs with idiopathic pericardial effusion reveals epicardial and pericardial thickening with associated inflammation. Besides benign idiopathic pericardial effusions, the three most common neoplasms that cause pericardial effusion are hemangiosarcoma, aortic body tumors, and mesothelioma. Hemangiosarcoma constitutes 60% to 75% of all neoplasms that cause pericardial effusion in dogs. This tumor most commonly arises from the right atrial appendage. German shepherds and golden retrievers are reportedly predisposed. Metastasis to the lungs, spleen, and other organs is usually present in affected dogs at the time of diagnosis. Aortic body tumors, also termed chemodectomas, are found in approximately 10% of dogs with pericardial effusion. They arise from chemoreceptors in the pulmonary artery and aortic outflow tract. Brachycephalic breeds are believed to be predisposed to aortic body tumors. These tumors tend to be slow growing and are locally invasive. Up to 80% of dogs diagnosed with heart-base tumors have pericardial effusion at the time of diagnosis. Mesothelioma is the most common primary tumor of the pericardium. It occurs in approximately 5% of dogs with pericardial effusion.6 Pericardial involvement may occur in isolation or in combination with other mesothelial surfaces. Male dogs are reportedly predisposed to the development of mesothelioma. The aim of the creation of a window in the pericardium or the performance of subtotal pericardectomy is to establish permanent drainage for patients with pericardial effusion. Thus, pericardectomy is considered to be the definitive treatment for recurrent benign or idiopathic pericardial effusion and constrictive pericarditis.7 This procedure is also advocated as a palliative treatment for malignant pericardial effusion.1-3,8,9 Pericardectomy was also recently recommended as an additional surgical procedure for the treatment of chylothorax in both dogs and cats.10-12 In a previous study of dogs with ultrasonographically detected pericardial effusion without cardiac masses, the median survival time was 1218 days among dogs that underwent pericardectomy and 532 days among dogs that underwent conservative management.3 Another study of dogs with heart-base tumors found a prolonged median survival time of 730 days among dogs that underwent pericardectomy and only 42 days among dogs that did not undergo pericardectomy.13 In contrast, the survival times of dogs with right atrial masses and suspected hemangiosarcoma are largely unaffected by pericardectomy.14 Pericardectomy has traditionally been performed by open thoracic surgery, either by median sternotomy or an intercostal approach.15 Balloon pericardiotomy has been proposed as an alternative approach.9,16,17 This technique was applied with a moderate success rate as a palliative treatment in three series of patients with benign or malignant pericardial effusion, although recurrence of pericardial effusion was noted in two of six dogs treated in one report.17 The first publication on thoracoscopic pericardectomy in the field of veterinary medicine appeared in 1999.18 In early studies, thoracoscopic pericardectomy was associated with less postoperative pain and lower morbidity than traditional open thoracotomy19 and had the additional benefit of offering better visualization secondary to improved illumination and magnification of previously inaccessible areas. More recently, pericardectomy has also been performed thoracoscopically in association with concurrent right atrial tumor removal20,21 and thoracoscopic management of chylothorax.22-24 The pericardium protects the heart from adjacent infection and malignancy and prevents its dislocation by fixing it within the thorax. The pericardium also restrains cardiac filling and enhances diastolic coupling of the ventricles. The pericardium consists of two distinct layers: the parietal pericardium, which is the tough outer fibroserous membrane, and the visceral pericardium (also termed the epicardium), which is the more delicate inner serous membrane firmly connected to the heart. The pericardial cavity is interposed between these two layers. Pericardial effusion is defined as the accumulation of fluid within this pericardial space. The fibrous pericardium is composed of a dense layer of collagen fibers. It is continuous with the adventitia of the great vessels at the heart base and with the sternopericardial ligament, which attaches the apex of the pericardium to the ventral aspect of the muscular diaphragm. In this fashion, the heart is anchored within the thorax. This anchorage is lost after pericardectomy. The parietal pericardium derives its blood supply from branches of the internal thoracic artery, the aorta, and superficial branches of the coronary arteries. Lymphatic drainage of the pericardial sac occurs mainly by vessels that empty into the pretracheal and cardiac lymph nodes and to a lesser extent by lymphatic vessels returning to the sternal lymph nodes. A thorough preoperative workup is necessary to diagnose or rule out tumor-associated pericardial effusion. In a study by MacDonald,4 107 dogs with pericardial effusion underwent echocardiographic examination and were subsequently evaluated by surgery (n = 48), necropsy (n = 44), or both (n = 15). The sensitivity and specificity of ultrasonography were 82% and 100%, respectively, for detection of a cardiac mass; 82% and 99%, respectively, for detection of a right atrial mass; and 74% and 98%, respectively, for detection of a heart-base mass. This information is of upmost importance when obtaining owner consent and choosing the optimal positions of the patient and surgical ports. As for any minimally invasive surgical procedure, only hemodynamically stable patients should undergo surgery. Preoperatively, a pericardiocentesis is recommended to decrease the risk of tamponade during surgery. The size of the patient is not an exclusion criterion; pericardectomy may even be performed on small cats.24 In such cases, a 2.7-mm, 30-degree scope can be used. Some owners may be reluctant to submit their pet to surgery when a tumor is suspected (especially hemangiosarcoma, which is associated with a poor prognosis). However, the size of the primary tumor, if present, rarely precludes the performance of a thoracoscopic pericardectomy. A preoperative diagnosis may be instrumental in decision making in such cases. As mentioned earlier, dogs with pericardial effusion secondary to neoplasia have a poor prognosis. Survival times range from 26 to 56 days, which is substantially shorter than the longer survival times of 790 to 1068 days in dogs with pericardial effusion secondary to non-neoplastic causes.2,3 However, dogs with heart-base tumors that undergo pericardectomy reportedly have longer survival times than that of dogs that do not undergo pericardectomy (median survival time, 730 vs. 42 days, respectively).13,25 Although in many cases, the etiology of idiopathic pericardial effusion remains unclear,15 determination of the cause of pericardial effusion provides valuable information regarding the most appropriate treatment and prognosis. Preoperative diagnosis, however, can be challenging. In one study, preoperative cytology had poor sensitivity26 and could not distinguish patients that may benefit from pericardectomy. The pH of the pericardial fluid was initially thought to aid in the differentiation between malignant and benign pericardial effusion (idiopathic)27; however, it has since been clearly shown to be of little diagnostic value. Recent evidence suggests that the blood concentration of cardiac troponin I is significantly higher in pericardial effusion from dogs with hemangiosarcoma compared with those with idiopathic pericardial effusion.28 Similarly histologic diagnosis can also be challenging. In a study of 14 dogs with idiopathic pericarditis evaluated using immunohistochemistry, Day and Martin29 found no features that clearly distinguished the specimens from dogs with neoplastic disease from those with idiopathic pericarditis. Moreover, a recent report30 on five golden retrievers with previously diagnosed idiopathic pericardial effusion that developed mesothelioma after an initial surgical intervention suggested malignant conversion of an originally benign process. Thoracoscopic creation of a 4- to 5-cm-diameter pericardial window has been recommended to palliate the clinical signs associated with pericardial effusion in dogs.18 In the study on which this recommendation is based, all dogs exhibited immediate resolution of cardiac tamponade after thoracoscopic partial pericardectomy. However, 77% of dogs had neoplastic pericardial effusion, and long-term follow-up was available for only two dogs with idiopathic pericardial effusion. Consequently, no conclusions could be made regarding the long-term outcome of dogs with idiopathic pericardial effusion that underwent the pericardial window procedure. Whether a 4- to 5-cm pericardial window is large enough for long-term palliation of the clinical signs in dogs is unknown. In one study,32 dogs with idiopathic pericardial effusion treated by thoracoscopic creation of a pericardial window had significantly shorter disease-free intervals and median survival times than did dogs treated by subtotal pericardectomy via thoracotomy (P <0.05). However, no significant differences were found between the two groups for dogs presented with neoplastic pericardial effusion. The authors suspected that this difference in the outcome may have been related to inaccuracy of the initial diagnosis (the excised pericardium was too small for accurate histopathologic diagnosis) or the inability of the pericardial window to palliate the signs of idiopathic pericardial effusion in the long term. Creation of a larger pericardial window or the performance of subtotal pericardectomy when performing thoracoscopic pericardectomy may be advisable.26 Although subtotal pericardectomy is more technically demanding, it can be performed with or without lung exclusion.26,31 Whenever it is possible, subphrenic pericardectomy is the author’s procedure of choice. Three approaches to thoracoscopic pericardectomy have been described depending on whether the patient is in lateral, dorsal, or sternal recumbency (when combined with thoracic duct surgery). The surgical preparation also depends on the chosen approach. For patients in lateral recumbency, the area from the scapular spine to the cranial abdomen and the area from the sternum to the dorsal spine are prepared. For patients in sternal recumbency, both sides of the chest are prepared to allow for entrance of an endoscope on each side of the chest.22 For patients in dorsal recumbency, which is the most common position, both sides of the chest are deliberately clipped from the sternum to the dorsal third of the rib cage. An adequate region of the cranial abdomen caudal to the xiphoid process is prepared to allow for possible transdiaphragmatic port placement. Given the short operative duration and sterile surgical environment, intraoperative broad-spectrum antibiotics are sufficient; postoperative antibiotic therapy is usually unnecessary. The patient and port positions depend mainly on the surgeon’s preference and patient’s disease. Dorsal recumbency is generally preferred in most patients. In that case, the operator needs to work from both sides of the chest and usually stays at the patient’s right side with the assistant holding the telescope with the left hand from the patient’s left side (Figure 33.1). Lateral recumbency is most often preferred in patients with heart-base tumors, although some authors reportedly select dorsal recumbency for such patients.21 Figure 33.1 Operating room layout for thoracoscopic pericardial window or subphrenic pericardectomy in dorsal recumbency
Thoracoscopic Pericardial Window and Subtotal Pericardectomy in Dogs and Cats
Preoperative Considerations
Surgical Anatomy
Diagnostic Workup and Imaging
Patient Selection
Prognostic Factors
Etiology of Pericardial Effusion
Minimally Invasive versus Open Surgery and Pericardial Window Procedure versus Subphrenic Pericardectomy
Patient Preparation
Surgical Preparation
Patient Positioning
Port Type and Positioning
Pericardectomy in Dorsal Recumbency26
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