How to Recognize a Pericardial Friction

1. What adjectives and analogies have been used to describe the quality of friction rubs?

ANS: They are usually described as crunching, scraping, creaking, grating, crackling, or scratching. They often sound like squeaky shoes or like two pieces of sandpaper rubbed against one another. Occasionally, however, they sound no different from any mixed-frequency murmur. They often sound surprisingly superficial, and increased stethoscope pressure sometimes seems to make them unexpectedly louder. They may sound as if they are halfway up the stethoscope tubing.

2. How many components are heard in most friction rubs?

ANS: Three: one systolic and two diastolic.

3. At what time in diastole do the two diastolic rubs occur?

ANS: a. In early diastole, near the end of early rapid expansion of the ventricle, at the time when an S3 would occur. b. At the end of diastole, when atrial contraction produces sudden ventricular expansion. This is the moment when an S4 would occur.

4. Where in systole may a systolic rub occur?

ANS: Anywhere. It may replace the first or second heart sound or occur only in mid-systole.

5. If one major rub replaces the first heart sound (the commonest occurrence) and two rubs occur in diastole, what is the cadence of the friction rubs that is heard as a background rhythm?

ANS: The cadence is the same as that of a quadruple rhythm due to a double

Note: Because the systolic rub may replace both the Sj and the S2, it is common to hear the rhythm as "CH-sh-sh-CH-sh-sh." When one of the diastolic rubs is absent, it is usually the S3, i.e., an S4 rub is the last to disappear, probably because the heart is maximally distended at the end of diastole, tending to bring the inflamed pericardial surfaces into contact.

Triphasic pericardial friction rub. A rub is recorded during atrial systole (ar), ventricular systole (sr), and mid-diastole (mdr). (From Spodick, D. H.: Acoustic phenomena in pericardial disease. Am. Heart J. 81:114-124, 1971. Reprinted with permission).

6. Is the friction rub usually louder during inspiration or expiration? Why?

ANS: In at least one-third of patients, it increases during inspiration [9]. This may be due to several possible causes:

a. The downward pull of the diaphragm on the pericardium may draw the pericardium more tautly over the heart. The diaphragm is attached to the pericardium, and it is conceivable that a small amount of fluid between the visceral and parietal pericardia could be squeezed out by the tightening of the two layers with inspiration.

b. It may be a pleuropericardial rub. Even when there is a pericardial effusion, there may still be a pericardial rub, and this may be accounted for either by the squeezing out of a small amount of fluid by inspiration or by the expanded lung pressing on the pericardium during inspiration. Therefore, in the presence of effusion the rub may only be heard with the patient supine in full inspiration.

7. Of the three major rub components, which one is almost always present? Which is the next most common component?

ANS: The systolic component is almost always present. The atrial systolic component is next in frequency of occurrence, but rarely does an atrial systolic rub occur alone as the only rub sound. It almost always occurs together with at least a systolic rub.

Note: You can exaggerate a doubtful rub by having the patient lie on elbows and knees to promote apposition of the visceral and parietal pericardium. This is especially useful when only the systolic phase remains.

8. Where are most friction rubs best heard?

ANS: Near the left sternal border, at about the third or fourth left interspace.

9. When is the friction rub transient?

ANS: During the course of acute myocardial infarction, when it may last only a few hours.

Note: In postmyocardial infarction syndrome (Dressier's syndrome), it may last for weeks.

10. In what clinical setting, besides uremia, is a pericardial friction rub most likely?

ANS: Immediately after open heart surgery.

Note: Immediately postoperative, a crunchy noise at the apex synchronous with the heart beat in the left lateral decubitus position is Hamman's sign of air in the mediastinum.

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