Pericardial Diseases

Pericardial Anatomy and Physiological Function

Structural Layers of the Pericardium:
- Fibrous Pericardium: The tough, outer protective shell.
- Serous Pericardium: A double-layered membrane formed by a continuous sheet folding over on itself:
  - Parietal Layer: The outer lining of the serous pericardium, adhering to the fibrous layer.
  - Visceral Layer: The inner lining of the serous pericardium, also known as the epicardium, which forms the outermost surface of the heart wall.
- Pericardial Space: A potential space situated between the parietal and visceral layers of the serous pericardium containing normal serous fluid.

Anatomic Insertions:
- Inserts posteriorly at the inferior vena cava (IVC).
- Inserts superiorly at the roots of the great vessels.
Normal Pericardial Fluid Volume:
- $20\text{--}50\,mL$
Physiological Functions:
- Limits acute distention of heart chambers.
- Distributes diastolic pressures evenly across the myocardium.
- Reduces friction between the moving heart and adjacent thoracic structures.
- Acts as a physical barrier against the spread of infection from neighboring tissues.

Pericardial Effusion

Pathophysiology & Hemodynamics:
- Pericardial effusion refers to an abnormal fluid accumulation within the pericardial sac, resulting from pericardial irritation, injury, or inflammation that triggers hypersecretion by the visceral pericardium.
- Hemodynamic consequences depend on both total fluid volume and the rate of accumulation.
- A large, rapidly accumulating effusion restricts left ventricular (LV) filling, causing Grade III Restrictive Diastolic Dysfunction and a subsequent drop in stroke volume.
Etiology by Category:
- Infection:
  - Viral etiologies
  - Bacterial etiologies (e.g., Tuberculosis / TB)
  - Parasitic infections
- Anasarca (Generalized Edema):
  - Liver failure
  - Right-sided heart failure
  - Chemotherapy side effects
- Inflammation:
  - Post-myocardial infarction (Dressler's Syndrome)
  - Systemic autoimmune diseases:
    - Lupus Erythematosus
    - Scleroderma
  - Radiation therapy
  - Uremia secondary to chronic renal failure
- Malignancy:
  - Primary cardiac tumors
  - Neoplastic invasion via direct extension (e.g., lung cancer, breast cancer)
  - Metastatic seeding (e.g., lymphoma, melanoma, leukemia)
- Iatrogenic:
  - Post-surgical complications
- Trauma
Clinical Presentation:
- Symptoms: Dyspnea and chest pain (typically exacerbated in a supine position).
- Physical Exam Signs: Elevated Jugular Venous Pressure (JVP) and muffled heart sounds during cardiac auscultation.
- Electrocardiogram (ECG):
  - Low Voltage ECG: Fluid surrounding the heart attenuates electrical signals.
  - Electrical Alternans: Beat-to-beat variation in QRS complex amplitude caused by the physical swinging motion of the heart within a large fluid effusion.

*   **Chest X-Ray (CXR)**: Cardiomegaly with an enlarged cardiac silhouette.

Role of 2D Echocardiography:
- Spatial Distribution:
  - Circumferential: Fluid communicates continuously around the entire heart; tends to collect in gravity-dependent posterior regions first.
  - Loculated: Fluid is isolated into discrete pockets or regions bounded by fibrous adhesions. Localized pressure spikes can severely compromise adjacent atrial filling.
- Anatomic Imaging Landmarks:
  - Assessed routinely in the Parasternal Long Axis (PLAX) view.
  - Pericardial fluid accumulates in the atrioventricular (AV) groove anterior to the descending aorta.
- Sequential Chamber Collapse Pathophysiology:
  - As pericardial pressure rises above intracardiac pressures, chambers collapse during their phase of lowest internal pressure:
    1. Right Atrial (RA) Collapse in Systole: The RA enters its lowest pressure phase during atrial relaxation (systole).
    2. Right Ventricular (RV) Collapse in Diastole: Further pressure increases cause RV collapse during early diastole; indicates impending or present cardiac tamponade.
    3. Right Atrial (RA) Collapse in Diastole: Occurs as intrapericardial pressure continues to rise.
Differentiation: Pleural Fluid vs. Pericardial Fluid:

Echocardiogram showing fluid relative to descending aorta

*   **Pleural Fluid**:
    *   Anatomic Position: Lies **posterior** to the descending aorta.
    *   Anterior Extent: Never extends anterior to the heart.
    *   Respiratory Dynamic: Changes in dimension with inspiration/expiration.
    *   Hemodynamic Effect: Does not cause cardiac chamber collapse.
*   **Pericardial Fluid**:
    *   Anatomic Position: Lies **anterior** to the descending aorta.
    *   AV Groove Behavior: Tapers at the AV sulcus.
    *   Respiratory Dynamic: Demonstrates no size change with respiration.
    *   Hemodynamic Effect: Can induce cardiac chamber collapse.

Echocardiographic Effusion Quantification:
- Measurement Standard: Measured at end-diastole in Parasternal Long Axis (PLAX) or Parasternal Short Axis (PSAX) views at the level of the papillary muscles.
- Physiologic:
  - Separation: $\sim 2\text{--}5\,mm$ space seen during systole only.
  - Volume: $20\text{--}50\,mL$
- Mild Effusion:
  - Separation: $<0.5\text{--}1.0\,cm$ space in both systole and diastole (typically posterior).
  - Volume: $50\text{--}100\,mL$
- Moderate Effusion:
  - Separation: $1.0\text{--}2.0\,cm$ posterior space in both systole and diastole.
  - Volume: $100\text{--}500\,mL$
- Large Effusion:
  - Separation: $>2.0\,cm$ combined anterior and posterior space in both systole and diastole.
  - Volume: $>500\,mL$
Echocardiographic Tissue Characterization & Interventions:
- Fluid Echogenicity:
  - Simple: Completely anechoic.
  - Complex: Contains internal echoes or fibrinous strands (characteristic of chronic or longstanding effusions).
- Hemopericardium:
  - Definition: Collection of blood within the pericardial cavity.
  - Mechanism: High antithrombotic activity within pericardial fluid prevents normal clotting, causing blood to remain fluid or form complex fibrin structures.
  - Causes: Myocardial wall perforation or ruptured pseudo-aneurysm.
  - Appearance: Echo-dense, complex fluid collection.
- Pericardial Thickness Assessment:
  - Evaluated visually as normal or hyperechoic/thickened (indicative of active or prior pericarditis).
- Doppler Evaluation:
  - Assesses diastolic filling profiles and respiratory variations across atrioventricular valves to exclude tamponade physiology.
- Therapeutic Management:
  - Pericardiocentesis: Echo-guided needle aspiration performed for:
    1. Diagnostic fluid analysis and etiology identification.
    2. Symptom relief and hemodynamic stabilization in cardiac tamponade.
    3. Volume reduction in large effusions ( $>2.0\,cm$ ).

Pericardial Tamponade

Pathophysiology:
- A life-threatening clinical syndrome caused by elevation of intrapericardial pressure from fluid accumulation (typically rapid onset moderate-to-large effusions).
- Elevated pericardial pressure exceeds normal intracardiac pressures, impairing diastolic filling of all heart chambers and severely depressing stroke volume and cardiac output.
Etiology Classification:
- Subacute / Chronic:
  - Pericarditis
  - Idiopathic pericardial effusion
  - Metastatic malignant disease
  - Radiation therapy
- Acute:
  - Blunt or penetrating trauma
  - Aortic dissection with rupture
  - Dressler's syndrome
  - Post-myocardial infarction free-wall rupture
  - Iatrogenic injury (post-surgical or cardiac catheterization)
Clinical Signs and Diagnostic Criteria:
- Beck's Triad (Classic Diagnostic Clinical Features):
  1. Hypotension (low systemic arterial blood pressure).
  2. Elevated Jugular Venous Pressure (distended neck veins).
  3. Distant, muffled heart sounds on auscultation.
- Kussmaul's Sign:
  - Definition: A paradoxical increase in Jugular Venous Pressure (JVP) during inspiration.
- Pulsus Paradoxus:
  - Definition: An exaggerated drop in systemic systolic blood pressure of $>10\,mmHg$ during normal inspiration.
  - Differential Etiologies: Also observed in pericarditis, Chronic Obstructive Pulmonary Disease (COPD), and croup.
- Electrocardiogram (ECG):
  - Sinus Tachycardia (compensatory mechanism to preserve cardiac output despite low stroke volume).
2D Echocardiographic Sequence of Chamber Collapse:

Diagram illustrating RA and RV collapse in systole and diastole

*   *Systolic Right Atrial (RA) Collapse*: Earliest indicator of rising pericardial pressure; not diagnostic of clinical tamponade on its own.
*   *Diastolic Right Ventricular (RV) Collapse*: Diagnostic hallmark of cardiac tamponade occurring when pericardial pressure exceeds early diastolic RV pressure.

Doppler Respiratory Inflow Variations:
- Mechanism: Respiratory changes alter ventricular filling dynamics reciprocally across the interventricular septum.
- Inspiration Physiology:
  - Right heart filling increases: Tricuspid Valve (TV) Peak E Velocity increases by $>50\%$ .
  - Left heart filling decreases: Mitral Valve (MV) Peak E Velocity decreases by $>25\%$ .
- Protocol for Doppler Acquisition:
  1. Reduce sweep speed to displays maximum cardiac cycles ( $>5\text{--}10$ beats per frame).
  2. Enable the echo unit respirometer ("Physio" option).
  3. Measure peak velocity on the first cardiac beat of inspiration and the first beat of expiration.
- Calculation Formula for Percentage Respiratory Variation: $\%\Delta = \frac{\text{1st beat Expiration} - \text{1st beat Inspiration}}{\text{1st beat Expiration}}$
  - Interpretation: A positive result indicates a reduction in peak inflow velocity during inspiration. A negative result reflects an increase in peak inflow velocity during inspiration.
- Worked Doppler Calculation Examples:
  - Example 1 (Tricuspid Valve Inflow):
    - Inspiratory 1st beat TV E velocity = $80\,cm/s$
    - Expiratory 1st beat TV E velocity = $55\,cm/s$
    - $\%\Delta = \frac{55 - 80}{55} = -0.4545 \rightarrow -45\%$
    - Result: $45\%$ increase in TV inflow velocity during inspiration ( $>50\%$ threshold reached).
  - Example 2 (Mitral Valve Inflow):
    - Inspiratory 1st beat MV E velocity = $65\,cm/s$
    - Expiratory 1st beat MV E velocity = $95\,cm/s$
    - $\%\Delta = \frac{95 - 65}{95} = 0.3157 \rightarrow 30\%$
    - Result: $30\%$ decrease in MV inflow velocity during inspiration ( $>25\%$ threshold reached).
Associated Echocardiographic Indicators:
- Respiratory Septal Shifting (Ventricular Interdependence):
  - During inspiration, increased right ventricular volume drives the Interventricular Septum (IVS) to bulge abnormally toward the Left Ventricle (LV).
- Inferior Vena Cava (IVC) Plethora:
  - Venous congestion causes the IVC to become dilated with absolute loss of inspiratory collapse ( $<50\%$ reduction in diameter).
Complications and Treatment:
- Complications: Severe hemodynamic compromise leading to cardiogenic shock, profound hypotension, and death.
- Urgent Management:
  - Pericardiocentesis: Emergency echo-guided fluid drainage.
  - Pericardial Window: Surgical excision of a pericardial tissue section allowing continuous fluid drainage into the pleural cavity; indicated for recurrent or chronic effusions.

Pericarditis and Constrictive Pericarditis

Acute Pericarditis Pathophysiology and Etiology:
- Definition: Acute inflammation of the pericardial layers often leading to pericardial thickening, fluid secretion, and fibrosis.
- Etiologies:
  - Viral or bacterial infections
  - Chest trauma
  - Iatrogenic surgical complications
  - Systemic autoimmune disorders (e.g., Lupus Erythematosus)
  - Neoplasms and radiation therapy
  - Dressler's Syndrome: Delayed autoimmune pericarditis (with or without effusion) occurring $1\text{--}8\text{ weeks}$ after an acute myocardial infarction, triggered by immune responses to necrotic tissue.
Clinical Diagnostics of Acute Pericarditis:
- Auscultation:
  - Pericardial Friction Rub: High-pitched scraping sound heard during diastole, generated by friction between inflamed pericardial layers containing fibrinous exudate.
- ECG:
  - Diffuse ST-segment Elevation: Widespread elevation across multiple lead groups, distinguishing it from local ST elevations seen in acute territorial myocardial infarction.
- Chest X-Ray:
  - Dense pericardial calcifications in chronic cases.
Constrictive Pericarditis (CP) Pathophysiology:
- Occurs when chronic inflammation leads to dense fibrosis, thickening, and calcification of the pericardium.
- The pericardium becomes a rigid outer shell surrounding the myocardium, restricting diastolic expansion of all chambers, raising filling pressures, and producing Grade III Restrictive Diastolic Filling.
Echocardiographic Features of Constrictive Pericarditis:
- 2D Imaging Features:
  - Thickened, highly echogenic pericardium (may exhibit fibrotic strands or internal thrombus).
  - Presence of pleural or variable pericardial effusions.
  - IVC Plethora.
- M-Mode Characteristics:

M-mode echocardiogram in constrictive pericarditis

    *   Pericardial layers appear thickened and intensely hyperechoic.
    *   Parallel motion of parietal and visceral layers moving together in lockstep, producing the classic **"railroad track" appearance**.
    *   Posterior LV wall displays restricted diastolic excursion ("flattening") and adherence to the underlying rigid pericardium.
*   **Pulse-Wave & Tissue Doppler Imaging (TDI) Findings**:
    *   Severe Grade III Restrictive Diastolic Profile:
        *   Markedly elevated Mitral Valve E/A ratio ( $>2.0$ 
        *   Shortened MV Deceleration Time ( $DT < 160\,ms$ 
        *   Shortened Isovolumic Relaxation Time (IVRT)
    *   **Annulus Reversus**:
        *   *Normal Dynamic*: Lateral mitral annulus peak velocity ( $e'$ ) is higher than septal annulus velocity ( $e'$ ) due to tethering of the septal wall.
        *   *Constrictive Dynamic*: Rigid pericardium fixes the lateral wall, reducing lateral mobility.
        *   *Diagnostic Finding*: **Lateral  $e'$  is lower than Septal  $e'$ ** (**Annulus Reversus**). Average  $e'$  velocity remains normal or elevated because restriction is extra-myocardial.

Differential Diagnosis: Constrictive Pericarditis (CP) vs. Restrictive Cardiomyopathy (RCM):
- Shared Hemodynamic Similarities:
  - Increased Mitral Valve E/A ratio ( $>2.0$
  - Decreased Mitral Valve Deceleration Time
  - Normal LV chamber size and baseline systolic function
- Key Diagnostic Differences:
  - Atrial Size:
    - Constrictive Pericarditis: Normal atrial dimensions (rigid pericardial boundary prevents bi-atrial expansion).
    - Restrictive Cardiomyopathy: Severe bi-atrial enlargement.
  - Pericardial Structure:
    - Constrictive Pericarditis: Thickened, hyperechoic, calcified pericardium.
    - Restrictive Cardiomyopathy: Normal pericardial thickness and echo density.
  - Tissue Doppler Velocities ( $e'$ ):
    - Constrictive Pericarditis: Lateral $e' < \text{Septal } e'$ (Annulus Reversus); average $e'$ often preserved.
    - Restrictive Cardiomyopathy: Average $e'$ severely depressed across both lateral and septal walls ( $<6\,cm/s$
  - Atrioventricular Valve Regurgitation:
    - Constrictive Pericarditis: Tricuspid Regurgitation (TR) and Mitral Regurgitation (MR) are infrequent.
    - Restrictive Cardiomyopathy: Significant TR and MR are common.
  - Respiratory Doppler Inflow Variation:
    - Constrictive Pericarditis: Marked variation present (Mitral Inflow shift $>25\%$ , Tricuspid Inflow shift $>50\%$ ).
    - Restrictive Cardiomyopathy: Absence of significant respiratory inflow variation.

Other Pericardial Pathologies

Pericardial Neoplasms & Masses:
- Metastatic Disease: Most common tumor involvement, arising primarily from lung cancer, breast cancer, lymphoma, or leukemia. Causes irregular cavity distortion and local tissue invasion.
- Mesothelioma: Malignant tumor originating directly from the serous lining membranes.
- Diagnostic Challenge: Difficult to differentiate acoustically from localized pericardial thrombus or organized fibrin clusters.
Pericardial Cysts:
- Characteristics: Benign, non-neoplastic, rare fluid-filled sacs.
- Etiology: Most commonly represent a persistent congenital remnant of a left superior vena cava (SVC).
Congenital Absence of the Pericardium:
- Characteristics: Extremely rare congenital malformation involving partial or complete pericardial wall absence.
Pneumo-Pericardium:
- Definition: Entrapment of free air within the pericardial cavity.
- Etiology: Typically secondary to traumatic esophageal tears or fistulas.
- Echocardiographic Appearance: Air blocks acoustic penetration completely, producing dense ring-down artifacts that obscure cardiac imaging visualization.