A pericardial rub is highly specific for acute pericarditis. It is generally heard over the left sternal border, louder at inspiration and on bending forward. In most cases, the rub is triphasic (audible in atrial, ventricular systole and ventricular diastole phases) and is of high frequency.[1]

The prevalence of a pericardial rub in pericarditis varies widely among studies and is anywhere between 35% and 85%,[2][3][4] likely depending on the examiner's expertise, and the frequency of cardiac auscultation since the pericardial rub might variably be audible during the day.[5] It was initially thought to be due to the friction of two inflamed pericardium. However, this does not explain the presence of a rub in large pericardial effusions where the pericardial layers are not in contact. Moreover, the occurrence of the pericardial rub does not seem to be related to the size of the effusion; it was found present in 31 to 54% of small effusions, 43 to -55% of moderate effusions and 42 to 49% of large effusions (p-value greater than 0.05 in both studies).[2][6] Also, pericardial rub seems to be more detected in patients with acute pericarditis than in those with a chronic pericardial disease (74.4% versus 15.2%, p less than 0.001).[2] Thus, the theory of inflamed pericardial layers friction does not seem to explain the occurrence of a pericardial rub fully. Natan et al. hypothesized that the rub might be the result of the movement of fibrin strands caused by inflammation.[6]

The presence and documentation of a pericardial rub are of extreme importance since it is one of the four criteria to diagnose acute pericarditis. According to the 2015 European Society of Cardiology Guidelines for the diagnosis and management of pericardial diseases, acute pericarditis is diagnosable in the presence of two out of the four criteria: typical pericarditis chest pain, pericardial rub, diffuse ST-elevation or PR-depression on electrocardiogram and a new or worsening pericardial effusion.[7]

Thus, detection of pericardial rub along with a new pericardial effusion, for example, meets the criteria and the patient should be treated as acute pericarditis. An untreated episode of acute pericarditis increases the risk of complications including recurrent, chronic and constrictive pericarditis.

A pericardial rub can also be indicative of left ventricular dilation after acute Q-wave anterior myocardial infarction since transmural infarct can irritate the pericardium (and cause pericarditis) and cause left ventricular failure.[8] The presence of pericardial rub after Q-wave anterior myocardial infarction might also carry a worse prognosis and indicate extensive ventricular damage after coronary angioplasty.[9][10]

Because of available technologies, expertise in bedside examination has declined among medical professionals. For every patient who presents with chest pain suspicious for acute pericarditis, the nursing and medical team should attentively try to identify a pericardial rub over the left sternal border at different times, since the presence of the rub is variable during the day. Its detection modifies the patient's management since the presence of a pericardial rub is very specific for acute pericarditis.