Echo-cardiogram - The importance of echo-cardiograms for pulmonary hypertension patients.
For many PH patients the first step towards being diagnosed with pulmonary arterial hypertension is undergoing an echo-cardiogram or echo. This is an important screening test for PAH. It is also used for routine surveillance of patients once they have been diagnosed with pulmonary hypertension. It is frequently used because it is noninvasive, relatively inexpensive, and very accessible, being available in many physician offices, outpatient settings and hospitals.
What is an echo cardiogram?
The echo cardiogram is a simple ultrasound of the heart performed by an ultrasound technician and read by a cardiologist. It is done with the patient lying down in a darkened room. The technician uses a computer with a transducer attachment and a clear jelly like substance. The jelly substance is wiped on the skin and helps the transducer’s accuracy. This is the same technology used to look at fetuses during pregnancy. The transducer is then pushed against the patient’s chest. It emits sound waves that “echo” back when they hit an object like a heart valve allowing a moving image to be seen on screen.
This test allows the physician to examine the chambers of the right side of the heart. They can tell if they are enlarged, if their walls are thickened, and if the septum (the wall between the right and the left side of the heart) looks like it should. This test also looks at the valves of the heart and can diagnosis congenital heart disease (like holes in the heart) or abnormal fluid around the heart (pericardial effusion). It can also estimate the pulmonary artery pressures using mathematical equations and the amount of blood being jetted back into the right atrium by the right ventricle.
Findings from an echo cardiogram can suggest a diagnosis of pulmonary hypertension.
There are several findings from an echo cardiogram that are suggestive of pulmonary hypertension. An enlarged right atrium, an enlarged right ventricle with a thick wall, septal shift (meaning the septum of the heart has been pushed into the left side of the heart by the enlarged chambers of the right side of the heart), and of course elevated pulmonary artery pressures are some of these results.
What to do if your echo cardiogram results suggest pulmonary hypertension
If a pulmonary hypertension specialist did not perform the echo cardiogram and it shows signs of pulmonary hypertension you may be referred to a PH specialist. The pulmonary hypertension expert will investigate how the results of the echo cardiogram correlate with the rest of the patient’s medical information and decide if further testing for pulmonary arterial hypertension is warranted. While the echo cardiogram is a useful tool, it cannot be used to officially diagnose PAH and treatment should not be initiated based on estimated pulmonary artery pressures from the echo. A right heart catheterization is currently the only way to officially diagnose pulmonary arterial hypertension.
A Detailed Look
This is the chamber that pumps blood full of oxygen into the aorta and throughout the entire body. The report should describe the size of the left ventricle. The walls may be normal in size, too thick or too thin. The squeeze of the ventricle is referred to as the Ejection Fraction. A normal ejection fraction is > or equal to 55%. This is the pumping capability of the ventricle. The relaxation phase of the ventricle is described by it’s diastology. This is much harder to measure accurately. Even when measured properly, the echo may miss major problems with the way in which the left ventricle relaxes. Unfortunately, many reports omit this section.
This chamber receives oxygenated blood from the lungs and conveys it to the left ventricle. The report should describe the size of the left ventricle.
This chamber pumps blood that is depleted of oxygen to the lungs where the blood will pick up oxygen. It pumps into the pulmonary arteries. The report should describe the size and function of the right ventricle. The shape of the right ventricle is more complex than the left ventricle so that a simple measure such as ejection fraction is generally not used. The walls are described as normal, too thin or too thick.
This chamber receives blood depleted of oxygen from the body and conveys it to the right ventricle. The report should comment on the size of the right atrium.
There are four valves in the heart. On the right side the Tricuspid valve separates the right atrium and ventricle (top and bottom chambers on the right side). The Pulmonic valve separates the right ventricle and the pulmonary arteries. On the left side of the heart, the Mitral valve separates the top and bottom chambers and the Aortic valve separates the left ventricle from the aorta. A detailed echo report should describe the function of each valve. Any degree of leakiness or narrowing should be commented upon and quantified.
Estimation of Pulmonary Artery Pressure
By measuring the velocity of blood that moves backwards across the Tricuspid valve, the echo can estimate the pressure in the pulmonary arteries. This relies on a modification of the Bernoulli equation. The equation is as follows:
Pulmonary Artery pressure = 4 x (TRV) 2 + RAP
TRV= tricuspid regurgitant velocity
RAP= Right atrial pressure
Echocardiography and Pulmonary
An echocardiogram (or echo) is an ultrasound-based test that can tell us a great deal about your heart. By bouncing and receiving ultrasound waves off your heart and adjacent structures, we can generate images of your heart. We can learn about the size and function of the right and left side of your heart and the valves. We can estimate pressures but not directly measure pressures. As we have emphasized in many different places on this website, an echocardiogram is not a substitute for a right heart catheterization. The diagnosis of PAH should never be made without a right heart catheterization and treatment should not be started until after a right heart catheterization is completed. Let’s take a more detailed look at the components of the echocardiogram report.
Why is the pulmonary artery pressure that is estimated by echocardiography often inaccurate? The key to understanding this lies in recognizing the sources of error.
1. The tricuspid regurgitant velocity is often very subjective. It depends on the quality of the echo images, the echo technician and the size of the patient and the amount of lung disease that the patient has.
2. The right atrial pressure can only be roughly inferred from characteristics of the hepatic veins and the inferior vena cava. Many labs just use 10mmHg. This practice is to be discouraged as it is rarely the best estimate of right atrial pressure
In patients with advanced lung disease, the pressure estimates are accurate about half the time.
This helps identify holes in your heart that allow blood to pass from the right side to the left side. A small intravenous catheter is placed in your vein. 9cc of saline and 1 cc of air are agitated together to create tiny bubbles. These bubbles are then injected vigorously into your vein. The bubbles should travel through your superior vena cava into your right atrium, through your right ventricle and be trapped in your lungs. If any bubbles are seen on the left side of your heart, there must be a communication. The most common communications are at the level of the atria (top chambers) and are called either persistent foramen ovale or an atrial septal defect. Less commonly, the communication may be between the ventricles and is called a ventricular septal defect. Another source of right to left communication is through abnormal vessels in your lungs (arterial-venous malformations). The timing of the appearance of bubbles on the left side of your heart can help determine the type of right to left communication.
This stands for tricuspid annular plane systolic excursion and is a measure of how well the right ventricle contracts. Normal values are at least 18-20 mm. Lower numbers suggest impaired squeeze of the right ventricle.
What can’t be measured on an echocardiogram?
1. The pressure in the left ventricle at the end of relaxation or LVEDP is unable to be measured with an echo.
2. The blood flow can’t be accurately measured with echo.
3. The pulmonary vascular resistance can’t be measured with an echo.