pericardial friction rub

**Pathophysiology:** Inflammation of the pericardium roughens the normally smooth, lubricated visceral and parietal surfaces (fibrinous exudate). Friction occurs as the heart moves within the sac. Classically the rub has up to three components corresponding to cardiac motion: (1) atrial systole (presystolic), (2) ventricular systole (the loudest and most commonly heard component), and (3) rapid ventricular filling in early diastole. A triphasic rub is the classic finding, though biphasic or monophasic rubs are also common. The rub can be evanescent and vary with position and time, so serial examination is useful.

**Exam characteristics:** - Scratchy, high-pitched, grating, "leather-on-leather" or "scratching sandpaper" quality - Best heard at the left lower sternal border (LLSB) with the diaphragm - Louder with the patient sitting up and leaning forward and with end-expiration (brings the heart closer to the chest wall) - Persists when the patient holds their breath. This distinguishes it from a pleural friction rub, which disappears with breath-holding. - Not affected much by respiration, unlike pleural rubs, which vary with breathing

**Clinical context (acute pericarditis):** - Symptoms: sharp, pleuritic chest pain that is relieved by sitting forward and worsened by lying supine, inspiration, or coughing. Pain may radiate to the trapezius ridge (phrenic nerve irritation). Fever may be present. - ECG: diffuse concave-up ST elevation with PR depression (and PR elevation with ST depression in aVR) - Etiologies: idiopathic/viral (Coxsackie B, most common), post-MI (early: days 1-3 from transmural inflammation; Dressler syndrome: weeks to months, autoimmune), uremia, malignancy, TB, autoimmune disease (SLE, RA), radiation, drugs (hydralazine, procainamide, isoniazid), and cardiac surgery or trauma - Treatment: NSAIDs (ibuprofen or aspirin) plus colchicine. Corticosteroids are reserved for refractory cases or specific causes, because they raise the risk of recurrence. Avoid NSAIDs and steroids early post-MI when possible, and use aspirin there.

**Key associations and complications:** - As an effusion accumulates, the rub may disappear because the layers are separated. Muffled heart sounds, hypotension, and JVD (Beck triad) suggest tamponade, and pulsus paradoxus and electrical alternans may occur. - Constrictive pericarditis can develop chronically (pericardial knock, Kussmaul sign) - A rub in uremic pericarditis is a classic indication to consider dialysis. Uremic pericarditis typically lacks the diffuse ST elevation seen in other causes.

**Differential for the sound:** - Pleural friction rub: varies with respiration and disappears with breath-holding - Pleuropericardial rub: has both cardiac and respiratory components - Murmurs: are lower pitched, and are often blowing, harsh, or rumbling in quality - Mediastinal crunch (Hamman sign): crunching sound synchronous with the heartbeat, caused by pneumomediastinum

**High-yield pearl:** A patient with pleuritic chest pain that improves on leaning forward, plus a scratchy 3-component sound at the LLSB and diffuse ST elevation, has acute pericarditis until proven otherwise.