What are the components of a pericardial rub?

Components of a Pericardial Rub

A pericardial friction rub can be mono-, bi-, or triphasic in nature, corresponding to cardiac movement during different phases of the cardiac cycle. 1

Characteristics of Pericardial Rub

The pericardial friction rub is a key diagnostic finding in acute pericarditis, occurring in approximately one-third of patients. It has several important components:

Phases of the Pericardial Rub

1. Triphasic rub - The classic complete form consisting of three components:

   • Atrial systole component
   • Ventricular systole component
   • Early diastolic component (ventricular filling)

2. Biphasic rub - Contains two components

   • Usually ventricular systole and early diastolic components

3. Monophasic rub - Single component

   • Most commonly the ventricular systolic component

Acoustic Qualities

• Described as a "scratching" or "sandpaper-like" sound 2
• High-pitched, scraping quality
• Superficial sound (close to the stethoscope)
• Best heard with the diaphragm of the stethoscope
• Intensity varies with respiration and body position

Detection Techniques

The pericardial friction rub has specific characteristics that help in its identification:

• Auscultation location: Best heard at the left lower sternal border
• Patient positioning: Often more prominent when the patient leans forward in a seated position
• Respiratory variation: May be accentuated during inspiration
• Pressure application: Can be enhanced by firm pressure with the stethoscope
• Timing: May be transient and can appear or disappear during examination 1

Clinical Significance

The presence of a pericardial rub is one of the four key diagnostic criteria for acute pericarditis, along with:

1. Pericarditic chest pain
2. ECG changes (widespread ST-elevation or PR depression)
3. Pericardial effusion (new or worsening) 1

Important Clinical Considerations

• A pericardial rub can be present with any amount of pericardial effusion - there is no significant correlation between the presence of a rub and the volume of effusion 3
• The rub may be absent in up to two-thirds of patients with acute pericarditis 1
• The rub is typically heard during the acute inflammatory phase and may disappear as the condition progresses
• In post-myocardial infarction pericarditis, the rub usually develops on day 2 or 3 after a transmural infarction 4

Pathophysiological Mechanism

Contrary to common belief, the pericardial friction rub may not be caused simply by the friction of roughened pericardial surfaces. Research suggests that:

• Fibrin strands formed during inflammation may connect the two pericardial layers
• These strands may function as "snares" that generate the characteristic sound through cardiac movement 3
• The inflammatory process causes the normally smooth, lubricated pericardial surfaces to become roughened

Clinical Pitfalls to Avoid

• Don't miss it: The rub can be transient - perform auscultation multiple times if pericarditis is suspected
• Don't dismiss mild effusions: The presence of a rub does not rule out significant pericardial effusion
• Don't confuse with pleural rubs: Pericardial rubs continue when breath is held, while pleural rubs cease
• Don't overlook in post-cardiac surgery patients: Pericardial rubs are common in post-pericardiotomy syndrome 2

The identification of a pericardial friction rub is a valuable clinical skill that can help in the early diagnosis of pericarditis, potentially preventing complications such as cardiac tamponade through prompt treatment.