Pericardial effusion is defined as the accumulation of fluid within the pericardial space. As the pressure within the pericardial
space increases, right sided cardiac filling is impaired, resulting in decreased stroke volume with subsequent decreases in
cardiac output and ultimately decreased oxygen delivery to the tissues (shock). These manifestations of pericardial effusion
are referred to as cardiac tamponade. Keys to the successful emergency management of dogs with life threatening pericardial
effusion depends on early triage, a thorough physical examination, point of care diagnostic imaging techniques, and subsequent
pericardiocentesis or placement of an indwelling pericardial drain.
Triage and Physical Examination in Pericardial Effusion
The most common presenting complaints from the owners of dogs with pericardial effusion and cardiac tamponade are lethargy,
anorexia, collapse or syncope, abdominal distention, and dyspnea. Major body systems assessment of the dog with pericardial
effusion will likely reveal compromise to one or all of the major body systems. Assessment of the cardiovascular system may
frequently reveal the following:
- Pale mucous membranes: due to vasoconstriction and poor peripheral perfusion
- Slow CRT: due to decreases in cardiac output
- Increased heart rate: due to compensatory activation of the sympathetic nervous system
- Poor pulse quality: due to decreased stroke volumes and low blood pressure
Assessment of the respiratory system will frequently reveal increased respiratory rate and effort.
Assessment of the central nervous system will frequently reveal a decreased level of consciousness secondary to decreased
oxygen delivery to the brain. Any one or combination of these findings should necessitate movement to the treatment area for
further assessment including full physical examination, measurement of blood pressure, oxygen saturation, cardiac rhythm (ECG),
and placement of an intravenous catheter from which a small blood sample for PCV / TS / Blood Glucose ± Venous Blood Gas and
Electrolytes can be rapidly acquired. If possible, blood for CBC, serum biochemical profile, and coagulation profile or ACT
should also be collected. Concurrently, a second team member will be able to collect a full medical history.
Physical examination should still be centered on the major body systems, but subtle findings supportive of pericardial effusion
may be noted including:
- Jugular venous distention ± jugular pulses: due to right sided congestive heart failure.
- Muffled heart sounds normal lung sounds: unlike pleural effusion which will frequently cause decreased heart and lung sounds,
pericardial effusion will frequently only cause decreased heart sounds.
- Abdominal distention: ascites and hepatic engorgement may result from longstanding (days) pericardial effusion / cardiac tamponade
due to right sided congestive heart failure. Abdominocentesis will frequently reveal a relatively clear fluid will low cellularity
and a protein concentration greater than 2.5g/dL but less than 3.5g/dL most consistent with a modified transudate.
- Pulsus paradoxus: An inspiratory fall of arterial systolic blood pressure of more than 10mmHg resulting in variation in pulse
intensity with respiratory cycle due to increased venous return during inspiration, increased right sided filling, shifting
of the interventricular septum to the left with decreased left sided diastolic filling and subsequent decreased left sided
stroke volume.
- Other physical examination findings specific to the underlying cause of the effusion such as fever in septic or fungal pericarditis.
Pericardial effusion causing cardiac tamponade should be HIGHLY suspected based on signalment, history, and physical examination
findings, supported by diagnostic testing such as abdominocentesis and electrocardiography ( ± radiography) and confirmed
through point of care diagnostic imaging techniques.
Diagnostic Techniques
Abdominocentesis: See above.
Electrocardiography: Assessment of ECG in patients with pericardial effusion may reveal sinus tachycardia ± ventricular arrhythmias. Ventricular
arrhythmias may result from decreased myocardial oxygen delivery or aberrant conduction associated with the underlying cause
of the effusion. QRS complexes <1mV in amplitude and the presence of electrical alternans (regular or irregular variation
in QRS complex amplitude associated with the heart moving within the pericardium to and from the positive pole of lead II)
are supportive of pericardial effusion.
