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Pericardial Knock

What Is It, Causes, Treatment, and More

Author: Corinne Tarantino, MPH

Editors: Ahaana Singh, Ian Mannarino, MD, MBA

Illustrator: Jillian Dunbar


What is a pericardial knock?

A pericardial knock is a high-pitched sound made by the heart due to early diastole, which is when 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.

What causes a pericardial knock?

A pericardial knock is most often caused when heart valves have lost elasticity, reducing their ability to close completely. Loss of elasticity is most commonly due to scarring (i.e., fibrosis) and sometimes calcifications brought about by constrictive pericarditis. Constrictive pericarditis is the long-term swelling of the pericardium, or the membrane surrounding the heart. This enlargement and stiffening of the pericardium limits the heart’s ability to expand and keep the atrioventricular valves open during diastole. Constrictive pericarditis can have many causes, including cancer, surgery, or chronic infections. 

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How do you diagnose and treat constrictive pericarditis?

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.

Without treatment, constrictive pericarditis can lead to heart failure and become life threatening. Initial treatment for constrictive pericarditis focuses on treating the underlying cause. If inflammation continues, anti-inflammatory medications or diuretics may be prescribed, and individuals may be recommended to reduce salt intake. However, constrictive pericarditis is often permanent and progressive, usually requiring a pericardiectomy, in which a portion or all of the pericardium is surgically removed from the heart. This surgery can be dangerous, and as the pericarditis progresses, the risk of complication increases.  

What are the most important facts to know about a pericardial knock?

A pericardial knock is a high-pitched sound that occurs in early diastole, or sudden cessation of ventricular filling. Pericardial knock is usually a sign of constrictive pericarditis, which is long-term swelling of the pericardium resulting in the development of scar tissue and potentially leading to heart failure. People with constrictive pericarditis may present with shortness of breath, weakness, and fatigue that slowly become worse over time. Constrictive pericarditis is often diagnosed by a physical exam and imaging tests, such as an electrocardiogram or echocardiogram. Early intervention may consist of medications and lifestyle changes. However, in more severe cases, pericardiectomy may be required.

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Related links

Pericardial disease: Clinical practice
Pericardial disease: Pathology review
Atrial fibrillation
Anatomy of the heart

Resources for research and reference

Bashore, T., Granger, C., Jackson, K., & Patel, M. (2021). Constrictive pericarditis. In M. Papadakis, S. McPhee, & M. Rabow (Eds.), Current medical diagnosis & treatment 2021 (60th ed.). McGraw Hill. 

Bhattad, P., & Jain, V. (2020). Constrictive pericarditis: A commonly missed cause of treatable diastolic heart failure. Cureus, 12(5): e8024. DOI: 10.7759/cureus.8024

Burgess, T., Le, N., Olds, G., Sullivan, P., & Mansoor, A. (2019). Pericardial knock. BMJ Case Reports, 12(12): e233546. DOI: 10.1136/bcr-2019-233546

Edwards, W. (2020, January 1). What is the role of electrocardiography in the workup of constrictive pericarditis? In Medscape. Retrieved January 23, 2021, from https://www.medscape.com/answers/157096-196905/what-is-the-role-of-electrocardiography-in-the-workup-of-constrictive-pericarditis 

Zulfiqar, S., & Veerasamy, M. (2017). Pericardial diseases. In A. Elmoselhi (Ed.), Cardiology: An integrated approach. McGraw-Hill.