Chapter 107 - Pericardial Surgery

Question 1

What are the 2 layers of the pericardium?

Answer 1

• Outer fibrous layer
• Inner serous layer (closed mesothelial lined sac with parietal and visceral layers)

Question 2

List the functions of the pericardium

Answer 2

• Keeps the heart in position
• Restrains cardiac filling
• Enhances diastolic ventricular coupling
• Protects against atrial rupture
• Prevent spread of infection or neoplasia to heart from pleural cavity
• Provides a gliding surface for heart motion

Question 3

What does pericardial fluid contain?
What is it’s oncotic pressure relative to serum?

Answer 3

Pericardial fluid is an ultrafiltrate of the serum
- phospholipids for lubrication
- Protein 1.7-3.6g/dL

• Colloid osmotic pressure is 25% of serum

Question 4

What are the physiologic effects of cardiac tamponade?

Answer 4

• Decreased cardiac output
• Increased central venous pressure
• Activation of compensatory RAAS and catecholamine release
• As atrial wall stretching is limited, atrial natriuretic peptide is not released to stop RAAS effects
• Increase in systemic venous and portal pressures causing jugular vein distention, liver congestion, ascites and peripheral edema
• Compression of coronary arteries causes poor myocardial perfusion
• Cardiogenic shock and death

Question 5

What is pulsus paradoxus?

Answer 5

A variation in systolic arterial pressures up to 10mmHg from increasing venous return during inspiration in a relatively nonexpandable heart (due to pericardial effusion)

NOT pathognomonic - Can also be seen with obstructive lung disease, restrictive cardiomyopathy or hypovolemic shock

Question 6

Parietal pericardium is not very compliant, after how much fluid accumulation do pressures increase?

Answer 6

5-60mL

Question 7

Chapter 107:What is a normal volume of pericardial fluid?

Answer 7

1-15mL

Question 8

What hemodynamic mechanism primarily causes reduced cardiac output in pericardial tamponade?

Answer 8

External pericardial pressure exceeds right atrial and ventricular diastolic pressures, limiting ventricular filling and reducing preload.

Question 9

Why does right atrial collapse occur earlier than left atrial collapse in cardiac tamponade?

Answer 9

Right atrial pressures are lower than left atrial pressures, making the right atrium more susceptible to external compression.

Question 10

What is the primary physiologic reason pulsus paradoxus occurs during pericardial tamponade?

Answer 10

Inspiratory increase in venous return shifts the interventricular septum leftward due to fixed pericardial volume, reducing left ventricular filling.

Question 11

Which physiologic compensation is activated early in pericardial tamponade?

Answer 11

Sympathetic activation increases heart rate and systemic vascular resistance to maintain perfusion.

Question 12

Why may pericardiocentesis temporarily worsen systemic hypotension?

Answer 12

Rapid decompression may acutely increase venous return and precipitate myocardial dysfunction in previously compressed ventricles.

Question 13

What is the most common cardiac tumor associated with right atrial hemangiosarcoma in dogs?

Answer 13

Right atrial hemangiosarcoma is most common, often located at the right auricle.

Question 14

Why is troponin I often elevated in dogs with cardiac hemangiosarcoma?

Answer 14

Myocardial infiltration or ischemia causes cardiomyocyte injury and troponin release.

Question 15

What echocardiographic feature most strongly supports tamponade physiology?

Answer 15

Diastolic collapse of the right atrium or right ventricle.

Question 16

Why does chronic pericardial effusion sometimes produce minimal clinical signs?

Answer 16

Slow accumulation allows pericardial stretch and adaptation, maintaining cardiac filling.

Question 17

What mechanism explains ascites in dogs with chronic pericardial effusion?

Answer 17

Elevated right-sided venous pressures lead to systemic venous congestion and transudation.

Question 18

Why is subtotal pericardiectomy preferred over pericardial window in many neoplastic cases?

Answer 18

It reduces recurrence of effusion by removing a larger portion of pericardium.

Question 19

What is the physiologic rationale for avoiding positive pressure ventilation in unstable tamponade patients?

Answer 19

Positive pressure reduces venous return and may further compromise preload.

Question 20

Why can pericardial effusion lead to equalization of diastolic pressures?

Answer 20

External compression limits chamber expansion, causing similar diastolic pressures across cardiac chambers.

Question 21

What is the primary cause of Beck’s triad in cardiac tamponade?

Answer 21

Elevated central venous pressure, hypotension, and muffled heart sounds from pericardial fluid accumulation.

Question 22

Why does pericardiectomy not treat restrictive cardiomyopathy?

Answer 22

Restrictive cardiomyopathy is due to intrinsic myocardial stiffness, not external constraint.

Question 23

What is the most common non-neoplastic cause of pericardial effusion in dogs?

Answer 23

Idiopathic hemorrhagic pericardial effusion.

Question 24

Why may pericardial fluid cytology fail to diagnose hemangiosarcoma?

Answer 24

Neoplastic cells exfoliate poorly and may be obscured by hemorrhage.

Question 25

What physiologic parameter most directly reflects preload limitation in tamponade?

Answer 25

Reduced stroke volume.

Question 26

Why is right ventricular diastolic collapse a late sign compared to right atrial collapse?

Answer 26

Right ventricular diastolic pressures exceed right atrial pressures during filling.

Question 27

What is the mechanism of hepatic congestion in chronic pericardial effusion?

Answer 27

Elevated central venous pressure impedes hepatic venous outflow.

Question 28

Why does pericardial effusion dampen heart sounds?

Answer 28

Fluid attenuates transmission of cardiac acoustic vibrations.

Question 29

What is the principal advantage of thoracoscopic pericardiectomy?

Answer 29

Reduced surgical morbidity while achieving adequate pericardial resection.

Question 30

Why is rapid removal of large pericardial effusions performed cautiously?

Answer 30

Abrupt hemodynamic shifts may precipitate arrhythmias or myocardial dysfunction.

Question 31

What electrocardiographic finding is classically associated with large pericardial effusions?

Answer 31

Electrical alternans due to cardiac swinging within fluid.

Question 32

Why may dogs with right atrial masses develop ventricular arrhythmias?

Answer 32

Myocardial invasion or irritation alters electrical conduction.

Question 33

What physiologic mechanism explains reduced pulse pressure in tamponade?

Answer 33

Reduced stroke volume lowers systolic pressure while diastolic pressure is maintained via vasoconstriction.

Question 34

Why is central venous pressure elevated in tamponade?

Answer 34

External compression prevents right atrial filling and venous return.

Question 35

What is the primary reason idiopathic pericardial effusion often resolves after pericardiectomy?

Answer 35

Removal of constraining pericardium prevents fluid reaccumulation from impairing filling.

Question 36

Why may pericardial effusion mimic right-sided heart failure clinically?

Answer 36

Both conditions produce systemic venous congestion and ascites.

Question 37

What is the physiologic consequence of pericardial constraint on ventricular interdependence?

Answer 37

Changes in one ventricular volume significantly affect the other due to fixed total pericardial volume.