RV Function

RV Anatomy

Unlike the LV, which has a relatively simple cylindrical shape, the geometry of the right ventricle is significantly more complex. As we will see later in this section, this hampers our ability to make volume assessments of the right ventricle, and RV performance is typically judged by other indices.

The right ventricle is often described as a crescent-shape that wraps around the septal wall of the left ventricle. It consists of a trabeculated inflow tract, an apical portion, and a smooth outflow tract that is the most anterior and superior portion of the RV. It is well known for the presence of the moderator band, which connects the anterior papillary muscle with the interventricular septum and is often easily seen on echo. The RV chamber is encircled by the borders of the RV lateral wall, or free wall, the interventricular septum, and the RV apex.

The complexity of RV geometry is far beyond my ability to recreate here, so I recommend you consult your favorite anatomy textbook for pictures as they will likely provide a better understanding than my brief attempt. This publication also includes some nice anatomical pictures of the right ventricle, as well as anatomic correlates to typical RV-focused TTE views.

RV Size

There are standard measurements that can be used to grade the size of the right ventricle, however the rule(s) of thumb below can be used for a quick assessment of RV size.

From the mid-esophageal 4 chamber view (or apical 4 with TTE):

A normal-sized RV should appear to have an area < 2/3 the area of the LV.

IF:

RV > 2/3 LV   -   MILD dilation

RV = LV   -   MODERATE dilation

RV > LV   -   SEVERE dilation        

RV Physiology

Just like the anatomy of the RV is unique in comparison to its more muscular neighbor, so is its physiology. The contractile force for RV systolic ejection comes primarily from two places: 1. longitudinal contraction of the RV base towards the apex (this is the primary contributor to RV contraction), and 2. contraction of the RV free wall against the interventricular septum. This is important to understand, particularly in the cardiac surgical population, since it explains how tricuspid valve procedures (ie. annuloplasties or tricuspid valve repairs) and conduction abnormalities that affect the motion of the interventricular septum (ie. ventricular epicardial pacing) can significantly impair RV function. It also provides a rational for why two of the most commonly used methods for assessing RV function measure only the downward motion of the tricuspid annulus.

Measuring RV Function

Due to complex geometry of the RV, a true EF is only able to be accurately measured by cardiac MRI. Because of this, assessment of RV function heavily on alternative methods.

TAPSE

TAPSE stands for Tricuspid Annular Plane Systolic Excursion, or, how far does the annulus of the tricuspid valve move down towards the apex during systole. Because the RV generate the majority of its contractile force from this downward movement of the tricuspid annulus, this measurement actually correlates reasonably well with RV function.

This is most easily measured using M mode with the cursor placed through the lateral annulus of the tricuspid valve. For the measurement to be valid, the apical motion of the tricuspid annulus must be parallel with the m-mode cursor. To measure this with TEE requires either a bit of software (often called "anatomic M-mode" or "AMM" to re-align the m-mode cursor to be parallel to the motion, or it requires some more advanced imaging from a transgastric location.

With the m-mode cursor appropriately placed, a tracing like the one below should be obtained. The movement of the tricuspid annulus can be seen typically as a bright "wave" at the appropriate depth on the m-mode display. The height difference between the peak and trough of the wave can then be measured, representing the total "TAPSE".

An abnormal TAPSE is < 17mm and is consistent with reduced RV systolic function.

RV S'

Where TAPSE measures the distance that the tricuspid annulus travles (in the apical-basal axis) during systole, the function can be similarly measured by tissue velocities through the use of tissue doppler. RV S' is the more commonly used cousin to mitral annular systolic velocity. Unfortunately for the transesophageal echocardiographer, this one is challenging to measure with TEE due to issues with doppler alignment  (though it remains one of my favorite methods to assess RV function with TTE). It also succeeds where mitral annular systolic velocities fail, since the downward motion of the tricuspid annulus actually contributes quite a bit to RV function and is more than just a proxy.

It can be measured by placing the tissue doppler (TDI) gate over the lateral annulus of the tricuspid valve to obtain a tracing like the one below. This does require appropriate alignment for doppler interrogation, which with TEE will have to be done from more advanced RV-focused transgastric views. I still include it here due to its usefulness in TTE, particularly when there may be dropout when trying to obtain an m-mode tracing to calculate a TAPSE. The S' wave correlates with a positive deflection (towards the probe) as the TV annulus moves towards the base during systole, generating a positive doppler velocity.

A normal RV S' is 10cm/s or greater

RV Fractional Area Change (FAC)

Fractional area change measures the percent change in area of the right ventricle as measured from a ME4C view on TEE, or an apical 4 chamber view on TTE. This is reported as a percentage, though it should not be confused with ejection fraction, as it has its own normal and abnormal range.

To measure RV FAC with TEE, record a representative cardiac cycle in the ME4C view and trace the area of the ventricle in its largest frame (end-diastolic volume or "EDV") and in its smallest frame (end-systole volume or "ESV"). Calculate as below:

RV FAC = (EDV - ESV) / EDV x 100%

A normal RV FAC is > 35%

RV dP/dt

Similar to how the rate of upslope of a mitral regurgitant jet can be used to assess LV contractility, RV function can be assessed using the TR jet envelope. First obtain a clear, continuous wave doppler tracing of the TR jet. Then measure the time it takes for the jet to rise from 1m/s to 2m/s. This value is dt. Since pressure = 4*(velocity^2), the pressure differential between 1m/s and 2m/s is 16mmHg - 1mmHg, or 15mmHg. This is dP. Thus follows the equation below:

dP / dt = (15mmHg) / (measured time interval from 1m/s to 2m/s)

A normal dP/dT for the right ventricle is > 400mmHg/s

(for those who prefer not to do math, this correleates with a dt > 37.5ms

Right Index of Myocardial Performance Index (RIMP)

The only quantitative measurement here that reflects both RV systolic AND diastolic function is the RIMP, sometimes also called the Tei index. This value reflects the sum of the isovolumetric relaxation and contraction times, divided by the ejection time. A healthy RV will have shorter durations of isovolumetric relaxation and contraction, as it is able to both relax and generate pressure quickly, thus will have a lower numberator and lower RIMP. Stiff and poorly contractile RVs will have longer isovolumetric times, causing a higher numberator and higher RIMP values.

RIMP = (IVRT + IVCT) / Ejection Time

This can be calculated by one of two ways:

Tissue Doppler Imaging:

Typical tissue doppler through the lateral tricuspid valve annulus will show three different waves: an S' wave during systole as the annulus moves towards the apex, an E' wave during diastole as the ventricle fills, and finally an A' wave corresponding with atrial contraction. Since TDI measures the velocity of tissue movement towards and away from the probe, the times when the waveform is at 0m/s correspond with isovolumetric times, when the annulus is not moving. IVRT can be measured by measuring the time in between the end of the S' wave and the beginning of the E' wave, and IVCT is the time between the end of the A' wave and the beginning of the S' wave. Ejection time is simply the total duration of the S' wave.

Continuous Wave Doppler

These times can also be derived using continuous wave doppler through the pulmonic and tricuspid valves. During systole, blood flows out of the pulmonic valve and towards the TEE probe which will create a doppler envelope whose total duration corresponds with the RV ejection time. Interestingly, the TR envelope will be slightly longer in duration. Why is this? The diastolic pressure in the main pulmonary artery is much higher than the right atrial pressure, thus in systole, the pressure in the RV will rise above the RA pressure before it rises above the PA pressure. Hence, the TR jet and its CWD envelope will begin before blood is actually ejected through the pulmonic valve. This small but notable time difference corresponds with the IVCT. Because of the low RAP compared with the PA pressure, the TR envelope will also continue slightly beyond the time at which the pulmonic valve closes and ejection ends. This small time interval corresponds with IVRT. Thus, the RIMP can be calculated by the following equation:

RIMP = (TR duration - PV duration) / PV duration

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Because of slight differences in the durations measured using TDI or CWD, there are different normal values depending on which technique is used.

A normal RIMP is < 0.43 if calculated using CWD or PWD.

A normal RIMP is < 0.54 if calculated using TDI.

RV Diastology