Pulsed Doppler Examination of the Heart

What is Pulsed Doppler Ultrasound?

Pulsed Doppler ultrasound consists of displaying the blood flow patterns in a waveform. The pulsed Doppler enables the physician to record different flow patterns during the cardiac cycle from specific parts of the heart. From these waveforms measurements can be made to assist the physician in the interpretation of blood flow into and out of the heart.

How Does the Pulsed Doppler Relate to the Electrocardiogram?

The electrocardiogram, also known as an EKG, is a recording of the electrical activity of the heart during the cardiac cycle. To understand the pulsed Doppler waveform recorded from the heart researchers have compared it to the EKG. From this comparison, we know which part of the heart cycle the Doppler waveforms are equivalent to.

This illustrates the electrical conduction of the heart. The electrical signal originates in the SA Node located near the right atrium. It is first sent the atrial walls, resulting in contraction of the atrial chambers. The signal then is transmitted to the AV Node (green) to the ventricles. When this occurs the ventricles contract.

This illustrates the correlation between the EKG and Doppler waveforms recorded from within the left ventricle. The green bar illustrates the waveform during early diastole. This occurs as the mitral valve opens, allowing blood to flow freely from the left atrium into the left ventricle. This is represented by the E wave on the Doppler recording. The blue bar represents atrial systole. As the atria contract (P wave on the EKG) blood remaining within the left atrium is forced into the left ventricle as represented by the A wave on the Doppler waveform. Once the ventricle is filled with blood, the ventricle begins to contract, as represented by the yellow shading. This is represented on the EKG by the QRS waveforms and the systolic waveform on the Doppler recording.

Are The Doppler Waveforms Different When Recorded From the Right and Left Sides of the Heart?

Yes, the waveforms are different. For example, when the pulsed Doppler is recorded from the left ventricle the diastolic and systolic waveforms can be recorded at the same time. The reason for this is because the mitral and aortic valves are next to each other. However, these valves are not close together for the right ventricle and the waveforms must be recorded separately from different locations within the heart.

This compares the pulsed Doppler waveforms recorded from within the left and right ventricles (inflow) and the pulmonary and aortic outflow tracts (outflow). The waveforms from the inflow tracts are different because the left ventricle displays two waveforms. This is because the mitral and aortic valves are adjacent to each other, resulting in both waveforms being recorded simultaneously. However, the aortic waveform within the left ventricle represents the flow exiting the left ventricle before it exits through the aortic valve.

How are the Doppler Waveforms Analyzed?

Measurement of the Doppler waveforms is compared to the age of the fetus. The following graphs illustrate the normal distribution of measurements for the waveforms recorded from the fetal heart.

Upper Panel. The represents various measurements that are made from the waveform. These measurements can identify abnormal blood flow patterns often observed in fetal disease states.

Lower Panel. This illustrates changes in the E and A waves as a function of the age of the fetus. As the fetus ages, the E wave form increases in height, representing an increase in speed as blood enters the ventricular chambers during the early filling phase of diastole. However, the A wave form does not increase in speed as the fetus ages. This suggests that the speed of blood resulting from atrial contraction remains unchanged, irrespective of the age of the fetus.

Upper Panel. These are various measurements that can be made to evaluate function of ventricles as they contract. Variations in these measurements can identify certain types of fetal disease states.

Lower Panel. This demonstrates that the speed of blood exiting the ventricles increases as the fetus grows. This suggests that the ventricles are able to increase their strength of contraction as they become larger secondary to fetal growth.

E/A Ratio

This is a measurement of the compliance or stiffness of the ventricles as blood enters the chamber during diastole. In certain fetal conditions the measurement of this ratio may be altered.

This graph illustrates the normal range for the E/A ratio. If the ratio decreases, cardiac dysfunction.

Peak Velocity

This measures the speed at which blood is ejected from the ventricles. When the heart is not functioning properly,then the peak velocity may decrease.

This illustrates the normal range for the peak velocity of the aorta. If this decreases, this suggests cardiac dysfunction.

Time-to-Peak Velocity

This is a measure of how much resistance there is to blood as it is being pumped out of the ventricle. If the value increases, this means there is less resistance than normal. If it decreases, this means that there is more resistance to blood flow. This is often observed in fetuses with abnormal growth in which the fetus is smaller than normal.