Pulsus paradoxus is an exaggerated response from the normal physiologic drop in blood pressure that occurs with inspiration. Normally, up to a 10-mmHg drop in systolic blood pressure can occur with inspiration. In cardiac tamponade, multiple factors lead to a larger-than-usual drop in systolic blood pressure with inspiration. Right ventricular filling is augmented over left ventricular filling, causing the interventricular septum to bulge into the left ventricle with a resultant drop in stroke volume.
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The lower stroke volume with inspiration is then reflected in lower blood pressure.
Pulsus paradoxus is measured in the following manner: With the patient breathing normally, the cuff is inflated and then deflated very slowly until Korotkoff sounds are first heard intermittently (representing the sound during expiration). Then, the cuff is further slowly deflated until all beats are heard (representing the sound during inspiration). The difference between the two pressures is defined as the pulsus paradoxus. On physical examination, pulsus paradoxus also can be detected by a decrease in the amplitude of the palpated carotid or femoral pulse during inspiration.
Is tamponade always associated with pulsus paradoxus?
No. Tamponade may occur without pulsus paradoxus when there is coexistent atrial septal defect, aortic insufficiency, or preexisting elevated left ventricular diastolic pressure (as in left ventricular hypertrophy). Also, pulsus paradoxus may occur without tamponade as in chronic obstructive pulmonary disease, right ventricular infarction, and pulmonary embolism.
What are two of the classic ECG changes of pericardial effusion?
Diffuse low voltages and electrical alternans may be seen with pericardial effusions. Changes in the QRS voltage is not only due to the amount of fluid but also the electrical conductivity of the fluid. In canine studies, saline introduced into the pericardial space produced a greater voltage reduction than blood.
Electrical alternans is a repetitive alternating change in the P, QRS, and T-wave amplitudes that occasionally occurs with cardiac tamponade. Most commonly, the QRS alone shows the alternating amplitude. The swinging motion of the heart in a relatively large volume of pericardial fluid is thought to produce electrical alternans. Sometimes electrical alternans is noticeable in only one lead and could therefore be missed on a bedside cardiac monitor. It should be noted that electrical alternans may occur in other conditions, such as paroxysmal supraventricular tachycardia, hypertension, and acute episodes of ischemia.
Outline the treatment of acute pericarditis.
Treat the underlying cause whenever possible. For example, treatment of rheumatoid arthritis or systemic lupus erythematosus may help lead to the resolution of associated pericarditis.
Analgesic agents. Codeine, 15-30 mg every 4-6 hours, usually provides adequate pain relief.
Anti-inflammatory agents. Aspirin, 650 mg every 3-4 hours, may be tried initially. Indomethacin, 25-50-mg doses four times/day, is a very effective form of treatment either initially or when aspirin has not provided adequate relief. The use of corticosteroids is controversial; many authors consider steroid use as an absolute last resort, as it may become very difficult to withdraw the therapy without precipitating relapses.
What is the role of echocardiography in the diagnosis of pericarditis and cardiac tamponade?
The echocardiogram is the most sensitive test for the detection of pericardial effusion. As little as 15 ml of fluid can be detected by two-dimensional echocardiography. Pericardial fluid appears as an echo-free space between the walls of the heart and pericardium (see figure). In tamponade, the cardiac chambers may appear underfilled and contracted. Collapse of the right atrium and right ventricle during diastole is virtually diagnostic of cardiac tamponade. Right atrial collapse tends to occur earlier and may be detected at a time when no clinical signs of tamponade exist, making it less specific for diagnosing tamponade than right ventricular collapse. The echocardiogram can also be used to guide placement of the needle used in pericardiocentesis.
Two-dimensional echocardiogram from a patient with pericardial effusion (LV = left ventricle, RV = right ventricle).