Pericardial Disease

Question 1

Describe the anatomy of the perciardium

Answer 1

• 2 membranes / layers
  
  • Outer fibrous parietal membrane
  • Inner serous visceral membrane
• Base of the fibrous membrane is continued on the great vessels and blends with their adventitia
• Apex of the fibrous membrane continues to the diaphragm as the phrenicopericardial ligament
• Small volume of fluid between layers helps to lubricate and reduce friction
• Parietal layer is composed of mesothelial cells and compactly arranged collagen with less abundant elastin fibres - fibroelastic properties

Question 2

Describe the physiological role of the pericardium

Answer 2

1. Functions to limit over distension - especially of the right heart when diastolic pressures are increased
2. Has a role in protecting the heart from infection
3. Limits the chances of adhesion forming between the heart and adjacent structures (eg. lungs)
4. Holds the heart in a fixed position in the thorax
5. Helps to inter-regulate the stroke volume between the two ventricles
6. Lubrication function reduces any friction during the cardiac cycle.

Question 3

List the various diseases with pericardial involvement of clinical significance in dogs and cats

Answer 3

1. Pericardial effusion
   
   • Neoplasia
   • Idiopathic
   • Pericarditis
   • Infection - rare
   • Atrial rupture
2. Congenital disorders
   
   • Peritoneopericardial diaphragmatic hernia (PPDH)
   • Pericardial cyst
   • Pericardial defects - typically allowing auricular herniation
3. Constrictive pericarditis
   
   • Usually secondary to idiopathic causes
   • Often secondary to recurrent pericardial effusion
4. Congestive heart failure
   
   • Most common cause for effusion in cats
   • The effusion is rarely of clinical significance

Question 4

Discuss the clinical presentation and diagnostic pathway for dogs or cats with PPDH

Answer 4

• PPDH is a congenital defect that allows communication between the peritoneal and pericardial cavities
• Medium and long haired cats, Maine Coons, Himalayans and weimaraners are predisposed
• ~50% of animals are diagnosed later in life and the finding is often incidental
• Clinical animals typically show either respiratory of GIT signs
  
  • tachypnoea or respiratory distress
  • vomiting or inappetance
• Clinical examination often reveals muffled heart sounds, tachypnoea or thoracic borborygmus
  
  • Sternal malformations are common, as may be cranioventral abdominal herniation
• Thoracic radiographs are usually suggestive if not diagnostic of PPDH
• Echocardiography should be diagnostic in experienced hands

Question 5

Stepwise describe the pathophysiological consequences of progressive build up of pericardial effusion

Answer 5

• Small volumes that are slow to accumulate are well tolerated. The parietal pericardium stretches to accomodate with minimal to no impact of diastolic cardiac function
• As intra-pericardial pressure increases (either due to rapid accumulation of small volumes or slow accumulation of large volumes), that pressure is equally transmitted to the entire heart
• Increased pericardial pressures primarily affect the lower pressure and more compliant right side of the heart leading to cardiac tamponade
• Tamponade leads to reduced right sided diastolic filling
  
  • Reduced systemic venous return
  • Reduced RA and RV filling and stroke volume
  • Reduced venous return to the left heart
  • Left ventricular stroke volume is reduced while systolic function is maintained
    
    • Reduced cardiac output leads to arterial hypotension and CARDIOGENIC SHOCK
• Diastolic collapse of the right heart occurs when output is reduced by 20% and BEFORE systemic arterial hypotension
• Neurohormonal activation occurs in tamponade, slightly differently to other causes of CHF
  
  • SNS is differentially activated - increased to the heart, adrenal and liver, inhibited to the kidney to enhance volume preservation
  • RAAS activation occurs as normal
  • ANP is not increased
    
    • Leads to Na+ preservation and contributes to volume overload
• Systemic volume overload and increased systemic venous pressures predominate

Question 6

Discuss the utility of pericardial fluid analysis

Answer 6

• Fluid analysis alone has a low diagnostic utility and specificity
• Fluid analysis is “non-diagnostic” in ~87-92.3% of dogs
• Typical haemorrhagic effusion is seen in ~85% of cases
• Mesothelial reactivity is common, seen in ~50% of cases
  
  • Cannot be used to diagnose mesothelioma
• Some neoplastic conditions may be diagnosed via fluid analysis
  
  • Round cell neoplasia. Diagnostic in 11/12 cases of cardiac lymphoma)
  • epithelioid/haemic neoplasia confirmed or suggested in 4/250 cases - low sensitivity
• Infective pericarditis including that caused by coccidoides immitis should be diagnosed with pericardial fluid analysis +/- culture
• Fluid pH has a variable and wide overlap between different aetiologies

Question 7

Discuss the treatment options for the causes of pericardial effusion

Answer 7

• Idiopathic pericardial effusion
  
  • Pericardiocentesis will be “curative” for ~50% of dogs, with recurrence in ~50%.
  • Subtotal pericardectomy is curative
    
    • Prognosis with subtotal pericardectomy is superior to performing a pericardial window tecnhique
• Constrictive pericarditis
  
  • Subtotal pericardectomy is the treatment of choice
  • Prognosis is largely dependent on the involvement or lack thereof of the visceral pericardium
    
    • Series of 13 dogs - 8 had parietal involvement only, 5 had visceral involvement with a 60% chance of surgery resolving the problem.
    • C Immitis infection carries a ~23.5 % mortality rate but may be treated long term with surgery and anti-fungal treatment.
• Neoplastic effusion
  
  • Unless primary right auricular tumour is amenable to excision, pericardial surgery is typically not indicated for suspected HSA
  • Subtotal pericardectomy for dogs with heart base mases - improved prognosis from 42 to 730 days
  • Pericardiocentesis may provide temporary relief only
  • Doxorubicin chemotherapy
    
    • Retrospective study of 64 dogs treated (versus 76 that were not) had a median survival of 116 days