J. Brad Case, DVM, MS, DACVS
Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
Indications for Pericardectomy
Pathologic pericardial effusion can result from malignancy, infectious or idiopathic etiologies. Among malignant causes, hemangiosarcoma of the right auricular appendage is most common, but aortic body chemodectoma and diffuse mesothelioma are also seen.1,2 Malignant pericardial effusion is diagnosed in about 70% and idiopathic pericardial effusion is seen in about 20–30% of dogs presenting for pathologic pericardial effusion.1,2 When the volume of effusion becomes significant, a reduction in end diastolic volume and cardiac output results, a condition referred to as cardiac tamponade. One of the most commonly performed VATS procedures in dogs is pericardectomy. The objective of pericardectomy is to excise enough pericardium to eliminate tamponade and to obtain a histologic diagnosis of the patient's condition.
The surgeon must decide how much pericardium to excise when considering pericardectomy. In palliative cases such as those associated with neoplastic effusions, a 4 x 4 cm pericardial window is adequate unless right auriculectomy is being considered.4 With presumed idiopathic cases, a complete pericardioscopic evaluation is necessary to reduce the chance of a missed diagnosis and a larger pericardectomy is indicated.5 Because masses are common on the right auricle and heart base, the surgeon must have adequate experience and understanding of the pericardial anatomy prior to performing pericardioscopy, auriculectomy or epicardial biopsy.
The orientation of the pericardial window is likely not as important as performing a thorough pericardioscopic assessment.5 This is particularly important in presumed idiopathic cases, because it is possible for small nodules and masses to be identified on endoscopy around the heart base in dogs with a preoperative negative echocardiogram.6 In this scenario, some dogs will be tentatively diagnosed with an idiopathic pericardial effusion. If a representative epicardial sample is not obtained during pericardioscopy and/or if the pericardial sample obtained is not representative of the underlying disease, then a missed diagnosis and lost opportunity for disease-specific medical therapy will occur.
Right auricular mass resection in combination with pericardectomy has recently been described in one and nine dogs.7,8 One dog died during surgery from hemorrhage but eight dogs underwent successful resection of the atrial mass. Dogs with masses limited to the tip of the atrial appendage were considered to be good candidates for a VATS auricular resection.8 The benefits of performing appendage resection in conjunction with pericardectomy are to obtain histologic diagnosis and to reduce the risk of hemorrhage from atrial rupture.7,8
Patient Preparation/Selection
In general, dogs that are stable enough for anesthesia and have either neoplastic or presumed idiopathic pericardial effusion are candidates for a VATS pericardectomy. However, constrictive pericarditis is a contraindication as the pericardium is typically severely fibrotic and adhered to the myocardium. Dogs with idiopathic chylothorax are also candidates for VATS pericardectomy. An important consideration prior to VATS pericardectomy is the size of the individual patient. Smaller dogs can be more difficult to maneuver instruments within the thoracic cavity and as such, may make for a challenging or risky pericardectomy procedure. Dogs as small as 8 kg have been reported to undergo successful VATS pericardectomy.5 The author has completed a pericardial window in a dog as small as 6 kg but has also converted to median sternotomy in another 6 kg dog. Therefore, dogs less than 6–10 kg are likely less ideal candidates for a VATS pericardectomy.
Positioning, Port Location and Procedure Descriptions
Dogs are clipped from the cranial abdomen to the caudal cervical region and dorsally to the level of the epaxial musculature. Standard aseptic preparation is necessary prior to surgery. Dogs are positioned in dorsal recumbency and the entire sternum should be accessible following patient draping. All port sites are infiltrated with bupivacaine prior to creation of the associated incision. A 5.5-mm camera/telescope port is placed in the subxiphoid region into the right hemithorax. A threaded Ternamian style cannula is preferred and the telescope should be inserted half way into the cannula during insertion to avoid iatrogenic pulmonary injury. A 5-mm 30-degree telescope is preferred as the field of view is adequate and the angled scope allows for evaluation of the majority of the pericardium and pericardial space during dissection and pericardioscopy. Once the telescope cannula is in position in the right hemithorax, a second 5.5-mm threaded blunt-end cannula is placed in an intercostal position in the ventral third of the thorax between the 7th and 9th intercostal spaces. The port is inserted under direct video observation. Blunt tip cannulas are preferred in the intercostal location to minimize the chance of intercostal artery rupture. A bipolar vessel sealing device is then used to dissect the mediastinum to create a clear view of the contralateral hemithorax. A third cannula (5.5- or 11.5-mm blunt tip) is then placed between the 7th and 9th intercostal spaces in the left hemithorax. Although an 11.5-mm cannula will accommodate a 10-mm vessel sealing device, the author has found that the larger end of the 10-mm device does not hold the often thickened pericardium as well as the 5.5-mm vessel sealing device. Thus, I prefer to use a 5-mm vessel sealing device for pericardectomy.
Pericardial Window
Following brief exploration of both hemithoraces, the pericardium is grasped at the cardiac apex with 5-mm endoscopic Babcock forceps and tented to allow a small opening to be made with endoscopic scissors. At this point hemorrhagic fluid will typically burst out of the pericardial space. The vessel sealing device is then introduced into this opening, and a square, approximately 4 x 4 cm pericardial window, centered on the midline over the cardiac apex, is created. It is necessary to alternate positions of the Babcock forceps and vessel sealing device between intercostal ports to facilitate completion of the pericardial window.
Pericardioscopy
If exploration of the pericardial space is indicated (e.g., presumed idiopathic effusion, auriculectomy) then a more substantial pericardectomy is indicated to improve visualization of the pericardial space.5,8,9 A few options exist to accomplish this goal including: performing a subphrenic pericardectomy,10 creating linear fenestrations in the remaining pericardium,11 or simply enlarging the pericardial window enough to allow evaluation of the heart base. In the case of presumed idiopathic effusions and auriculectomy, my preference is to enlarge the pericardial window longitudinally up to the heart base and to remove enough pericardium to facilitate uninterrupted visualization of the heart base and right auricular appendage. In dogs with chylothorax in which residual pericardium may cause some restriction of the myocardium, a subphrenic pericardectomy is indicated.
Subphrenic Pericardectomy
Subphrenic pericardectomy is typically defined as pericardectomy to within 1 cm ventral and parallel to the phrenic nerves and can be performed with or without one lung ventilation.10,12 Subphrenic pericardectomy is technically more challenging than pericardial window and its variations, but can be performed safely with appropriate technique. Subphrenic pericardectomy is initiated by incising the pericardium at the cardiac apex similar to pericardial window. A sealing device is then directed dorsally and caudally towards the phrenic nerves. Next the dog is tilted to the contralateral side ∼20 degrees and the telescope is moved to the ipsilateral instrument port and the sealing device moved to the subxyphoid port. At this point the pericardectomy is continued cranially parallel to the phrenic nerves. The procedure is then performed similarly on the contralateral side ultimately connecting the two lines of dissection. The pericardium should be removed using a specimen retrieval bag to limit the chance of port site metastasis. A chest drain should be placed under video observation prior to recovery.
Complications and Outcome
Hemorrhage from the great vessels, intercostal vessels and pericardium are possible but with careful attention to detail and technique, the risk of significant hemorrhage appears to be low. Thermal injury to pulmonary tissues may occur if visualization of lungs is obscured during pericardectomy. Cardiac arrhythmias (sometimes fatal) have been reported anecdotally by surgeons who perform VATS pericardectomy regularly. The presumption is collateral thermal injury by contact of the vessel sealing device with the myocardium. Care must be taken to avoid contact of any thermal energy device with the myocardium during pericardectomy.
Median disease-free interval for dogs with idiopathic pericardial effusion treated by VATS pericardial window was 11.6 months and was significantly worse than dogs treated by subtotal pericardectomy (median disease free interval not reached) in one recent study.5 However, dogs with a neoplastic cause for their pericardial effusion, experienced a similar disease free interval if treated with a pericardial window (median 2.7 months) or a subtotal pericardectomy (median 3.8 months).
Similarly, median survival time for dogs with idiopathic pericardial effusion treated by VATS pericardial window was 13.1 months and was significantly worse than dogs treated by subtotal pericardectomy (median survival not reached).5 However, dogs with a neoplastic cause for their pericardial effusion, experienced a similar median survival if treated with a pericardial window (median survival 2.7 months) or a subtotal pericardectomy (median survival 4.0 months).
The 1-, 2-, and 3-year survival rates for dogs with an idiopathic pericardial effusion undergoing VATS pericardial window were 58%, 35% and 35%, respectively. One-year survival for dogs with a neoplastic effusion undergoing VATS pericardial window was 9%.5
References
1. Berg RJ, Wingfield W. Pericardial effusion in the dog: a review of 42 cases. J Am Anim Hosp Assoc. 1984;20:721–730.
2. Dunning D, Monnet E, Orton EC, Salman MD. Analysis of prognostic indicators for dogs with pericardial effusion: 46 cases (1985–1996). J Am Vet Med Assoc. 1998;212:1276–1280.
3. Aronsohn MG, Carpenter JL. Surgical treatment of idiopathic pericardial effusion in the dog: 25 cases (1978–1993). J Am Anim Hosp Assoc. 1999;35:521–525.
4. Jackson J, Richter KP, Launer DP. Thoracoscopic partial pericardiectomy in 13 dogs. J Vet Intern Med. 1999;13:529–533.
5. Case JB, Maxwell M, Aman A, Monnet EL. Outcome evaluation of thoracoscopic creation of a pericardial window or subtotal pericardectomy via thoracotomy for the treatment of pericardial effusion in dogs. J Am Vet Med Assoc. 2013;242(4):493–498.
6. MacDonald KA, Cagney O, Magne ML. Echocardiographic and clinicopathologic characterization of pericardial effusion in dogs: 107 cases (1985–2006). J Am Vet Med Assoc. 2009; 235:1456–1461.
7. Crumbaker DM, Rooney MB, Case JB. Thoracoscopic subtotal pericardiectomy and right atrial mass resection in a dog. J Am Vet Med Assoc. 2010;237:551–554.
8. Ployart S, Libermann S, Doran I, et al. Thoracoscopic resection of right auricular masses in 9 dogs. In: Proceedings from the 9th Annual Meeting of the Veterinary Endoscopy Society; March 22–24, 2012; Park City, UT. Abstract.
9. Skinner OT, Case JB, Ellison GW, Monnet EL. Pericardioscopic imaging findings in cadaveric dogs: comparison of an apical pericardial window and sub-phrenic pericardectomy. Vet Surg. 2014;43(1):45–51.
10. Dupré GP, Corlouer J-P, Bouvy B. Thoracoscopic pericardectomy performed without pulmonary exclusion in 9 dogs. Vet Surg. 2001;30:21–27.
11. Radlinsky M. Pericardial window with pericardial fillet for the treatment of pericardial disease in dogs. In: Proceedings from the Veterinary Endoscopy Society Annual Meeting; May 15–17, 2014; Florence, Italy.
12. Mayhew KN, Mayhew PD, Sorrell-Raschi L, Brown DC. Thoracoscopic subphrenic pericardectomy using double-lumen endobronchial intubation for alternating one-lung ventilation. Vet Surg. 2009;38:961–966.