Introduction
The echocardiogram (ECHO) is a non-invasive technique to visualize the structures and function of the heart. It utilizes high frequency sound waves in a manner similar to ultrasonography.
The transthoracic echocardiogram (TTE) is the most commonly used echocardiogram to look for evidence of pulmonary hypertension.
- A transducer that emits high-frequency sound waves is placed over the ribs near the sternum and directed toward the heart. Other images are taken underneath and slightly left of the nipple and in the upper abdomen.
- The transducer picks up the echoes of sound waves and transmits them as electrical impulses. The echocardiograph converts these impulses into moving pictures of the heart.
- Pictures can be two-dimensional or three-dimensional, depending on the part of the heart being evaluated and the type of machine.
- Often, the images can be displayed using pseudocolor, a process which digitally colorizes various aspects of the image. The colors (usually red and blue) indicate the direction of blood flow away from or towards the Doppler transducer.
A Doppler echocardiogram uses a probe to record the motion of blood through the heart.
Figure reproduced with permission from NHLBI/NIH. http://www.nhlbi.nih.gov
A second type of ECHO called the transesophageal echocardiogram (TEE) is sometimes used when more detailed images are required
- In this procedure, the ECHO transducer is inserted into the patient’s esophagus (after pretreatment with local anesthetic).
- TEE usually provides a more stable image because the probe is stabilized within the esophagus. However, the number of visible aspects of the heart is reduced because the probe is relatively more fixed in position.
Figure reproduced with permission from NHLBI/NIH. http://www.nhlbi.nih.gov
ECHO can be used to estimate the pressures in the heart as well as the rates of blood flow through the heart chambers, valves, and vessels.
ECHO in the Diagnosis of PAH
It is important to note that ECHO should not be used to diagnose PAH. A right heart catheterization is required to make the diagnosis.
ECHO can provide:
- Estimate of RV pressure
- Tricuspid valve regurgitant “jet” (TR jet)
- Functional and morphologic sequelae of PAH [e.g. right ventricular enlargement (RVE)]
- Identification of potential cardiac causes of PAH
- Presence of pericardial effusion
- Presence of possible left heart disease
- Valvular heart disease (VHD)
Evidence for RA/RV enlargement or RV dysfunction should trigger further evaluation.
While ECHO is most often taken with the patient at rest, an exercise ECHO may be used when the patient experiences dyspnea upon exertion but pressure is normal on resting ECHO.
- Exercise ECHO is considered more difficult to perform and interpret.
- The 2009 JACC/AHA Guidelines recommend that treatment decisions not be based solely on the basis of exercise-induced PH.
- Exercise-induced PH has not been studied in randomized, clinical trials.
Figure 3 depicts an echocardiogram characteristic of PAH. As you can see in this video, the RA and RV is enlarged and the left ventricle is not pumping blood properly.
Video courtesy of Dr. Paul Forfia
Tricuspid Regurgitation (TR) Jet
Under Doppler ECHO, TR Jet velocity can be used to estimate pulmonary artery systolic pressure (PASP).
- In this method, the maximum velocity of the TR jet (measured via continuous Doppler) is added to the estimated RA pressure.
- RA pressure is commonly estimated by determining the variation in the size of the inferior vena cava with inspiration: complete collapse, right atrial pressure = 5 mmHg; partial collapse, right atrial pressure = 10 mmHg; and no collapse, right atrial pressure = 15 mmHg.
Figure 4 depicts a sample Doppler ECHO image from a patient with PAH with an estimated PASP of 50 mmHg.
Image courtesy of Dr. Paul Forfia
Figure 5 is an example of TR jet recordings by color Doppler in a patient with mild tricuspid regurgitation and another with severe tricuspid regurgitation.
Images courtesy of Dr. Paul Forfia
In these images, the red and blue pseudocolor enhancements represent blood moving towards (red) and away (blue) from the Doppler ECHO transducer. Thus, the relative size of these colorized jets indicates the level of tricuspid regurgitation.
Doppler ECHO can be used to estimate the relative sizes of the right and left ventricles (Figure 6).
Images courtesy of Dr. Paul Forfia
In the image on the right you can see that the right ventricle (outlined in blue) is enlarged, as is the case in PAH.
As pulmonary vascular resistance increases, most patients will eventually develop RV dysfunction (Figure 7)*.
Images courtesy of Dr. Paul Forfia
*TAPSE = tricuspid annular plane systolic excursion. This is a simple measure of RV function.
Pericardial Effusion
The most reported prognostic association with mortality in patients with PAH is the presence of pericardial effusion on ECHO examination. The cause of pericardial effusion in PAH is due to elevated right atrial pressure, which impairs venous and lymphatic drainage of the myocardium and is a representation of right ventricular diastolic dysfunction. Figure 8 demonstrates how a pericardial effusion is represented on ECHO.
Image courtesy of Dr. Paul Forfia
Summary
- Doppler echocardiogram is a recommended technique to assess the status of cardiac structures when a patient is suspected of having PAH.
- While a powerful tool, ECHO is not the defining technique to diagnose PAH. Rather, it is used to add to the “index of suspicion” of PAH.
- Transthoracic ECHO and transesophageal ECHO can provide estimates for right and left ventricle size, estimates of PASP, and tricuspid (and mitral) valve regurgitation.
- ECHO can also visualize the presence of pericardial effusion, which has a high association with mortality in patients with PAH.
- Interpretation of ECHO images is difficult, requiring a high degree of skill and training.
- In addition to being utilized as a screening tool for PAH, ECHO is often used in follow-up examinations of PAH patients to assess RV size and function over time.
References
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3. National Heart, Lung, and Blood Institute/National Institutes of Health. What To Expect During Echocardiography.
http://www.nhlbi.nih.gov/health/health-topics/topics/echo/during.html. Accessed September 30, 2013.
4. National Heart, Lung, and Blood Institute/National Institutes of Health. What To Expect During Transesophageal Echocardiography. http://www.nhlbi.nih.gov/health/health-topics/topics/tee/during.html.; Accessed September 30, 2013.
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