Pericardial Diseases and Anatomy

Pericardial Diseases

• Pericardial diseases involve the pericardium, a sac surrounding the heart
• Pericardial effusion (PE) is a common disorder, characterized by excessive fluid accumulation within the pericardial space
• PE can cause tamponade, a life-threatening condition, when the pressure in the pericardial sac becomes too high, restricting heart function

Pericardial Anatomy

• The pericardium consists of two layers: parietal pericardium (tough, outer layer) and visceral pericardium (delicate inner layer)
• The pericardial cavity is a potential space between these layers, containing a small amount of fluid (typically 1/4mL/kg body weight)
• This fluid reduces friction during heart movement

Functions of the Pericardium

• Anatomical fixation: prevents excessive heart movement with changes in body position
• Maintains optimal heart shape
• Prevents overdistension of heart chambers
• Supports ventricular coupling
• Reduces friction
• Provides a barrier against infection and malignant growth

Properties of Normal Pericardium

• Normal pressure within the pericardial space is about 0 (similar to pleural space)
• The pericardium has a limited reserve volume
• When fluid volume increases beyond the reserve limit, pericardial compliance dramatically decreases, and pressure rises quickly

Pericardial Effusion (PE)

• PE is the abnormal, excessive fluid accumulation in the pericardial space
• The most common pericardial disorder in veterinary patients
• Causes include neoplasia, infectious agents, trauma, and idiopathic cases
• PE can lead to cardiac tamponade and congestive heart failure (CHF)

Cardiac Tamponade

• Occurs when intrapericardial pressure rises to a level too high to allow proper venous return to the right heart
• The heart is effectively compressed, which impairs its function
• Results can include decreased preload, stroke volume, cardiac output, and potential death if not treated

Clinical Consequences of PE

• Chronic PE/Tamponade: Slow onset, likely from neoplastic effusion, possible activation of the renin-angiotensin-aldosterone system
• Acute PE/Tamponade: Rapid onset, often from hemorrhage, acute cases, decreased cardiac output, cardiogenic shock likely

Physical Examination Findings

• Jugular venous distension/pulsation
• Muffled heart sounds
• Systemic hypotension
• Tachycardia
• Abdominal distension
• Pulsus paradoxus (inspiratory decrease in arterial pulse pressure greater than 10mmHg)

Diagnostic Testing: Thoracic Radiographs

• "Globoid" cardiac silhouette without specific chamber enlargement
• Sharply defined ("crisp") margins of cardiac silhouette
• Bilateral contact between the cardiac silhouette and the thoracic wall

Diagnostic Testing: Echocardiography

• Used to confirm the presence of PE
• Allows assessment for tamponade
• Allows evaluation for cardiac and pericardial tumors

Causes of PE (Dog)

• Neoplastic: Right atrial hemangiosarcoma, heart base tumors, chemodectoma, ectopic thyroid carcinoma, mesothelioma, lymphoma, other primary or metastatic sarcomas/carcinomas
• Non-Neoplastic: Idiopathic hemorrhagic PE (most common), infectious (bacterial/fungal), traumatic, penetrating foreign bodies, coagulopathy, left atrial rupture, small volumes seen with uremia, hypoalbuminemia, congestive heart failure

Acute Management of PE

• Ultrasound-guided pericardiocentesis (pericardial "tap") is crucial
• Immediate, if the pet is stable
• Intravenous fluids, supportive treatment are often essential
• Avoid diuretics
• Emergency management required

"Chronic" Management of PE

• Fluid submitted from a "tap" may assist in diagnosis
• If not caused by aggressive neoplasia, pericardiectomy may be necessary
• Appropriate antimicrobial or other therapy is required based on diagnosis
• Continuous or intermittent pericardial drainage may be necessary