Pericardial Knock · What Is It, Causes, Treatment, and More

A pericardial knock is a high-pitched sound made by the heart due to early diastole, as a ventricle does not fully fill with blood between heartbeats. The sound generally indicates diastolic dysfunction, in which the heart is stiffened, has difficulty relaxing between beats, and cannot completely fill up with blood. 

The heart has four chambers: the right and left atria (i.e., the top chambers) and the right and left ventricles (i.e., the bottom chambers). In general, blood flows from veins into the atria, then into the ventricles, and out of the heart through the arteries. During the pumping of blood, there are two heart sounds that make up a “lub-dub” sound. The first heart sound (“lub”) is from the closing of the atrioventricular valves located between the atria and ventricles. The second sound (“dub”) is when the semilunar valves, which connect the ventricles to the arteries, close. Diastole occurs after the second sound and is when the heart relaxes and the ventricles fill with blood. The pericardial knock occurs early in diastole if the ventricles do not completely fill with blood.

To diagnose constrictive pericarditis, a clinician will often first assess the individual’s vital signs, symptoms, and medical history. One of the primary signs of constrictive pericarditis is hearing a pericardial knock during diastole when a provider listens to the heart sounds with a stethoscope. In addition, constrictive pericarditis is often accompanied by progressive shortness of breath, fatigue, and weakness. People with constrictive pericarditis usually present with chronic swelling of legs and arms (i.e., edema) and abdominal swelling (i.e., ascites). Another indicator of constrictive pericarditis is the Kussmaul sign, which can be observed when the individual’s jugular vein, the large vein in the neck, sticks out when the individual breathes in. 

Afterwards, diagnostic imaging may be performed, most commonly electrocardiography and echocardiography. An electrocardiography (ECG) records electrical impulses from the heart and may show a nonspecific finding, known as diffuse ST-T wave changes. In severe cases, the ECG can show an irregular, fast heart beat, known as atrial fibrillation. Unlike ECG, echocardiography creates images by using sound waves, and two types may be used for diagnosis of constrictive pericarditis: 2-D or Doppler. 2-D echocardiography can help visualize the thickened pericardium and other changes to the heart. Doppler echocardiography may show an unusually rapid early diastolic filling. 

Other tests, such as cardiac catheterization, in which a thin tube is inserted into the heart, or cardiac magnetic resonance imaging (MRI) may be necessary if diagnosis remains unclear. Occasionally, a chest X-ray may also be performed.