Chapter: LV Size and Function

LVH Septal Bulge LVEDD LV Function Athlete's Heart

LV Size & Function

This chapter provides an overview of quantitative assessment of the left ventricle's size and both systolic and diastolic function.

LV filling and output are maximal toward the end of expiration, when LV measurements should be made. A physician should direct a patient’s breathing to get the timing correct. Fortunately, most views of the LV are best toward the end of expiration. Some aspects of heart size and function vary with body height, so care is needed with very tall or short patients.

LV HYPERTROPHY (ENLARGEMENT)

Detecting and quantifying LV wall enlargement with ultrasound is complex. There are different forms of myocardial hypertrophy, which can be diffuse or localized. Diseases like amyloid, sarcoid, and Fabry cause wall enlargement from infiltration of non-myocardial tissue. Only measurement of the basal interventricular septum (IVS) at end diastole is needed for most patients. End diastole is the image with maximum LV chamber size and the mitral valve just floating shut.

The PLAX is a standard view to measure the IVS. The PLAX IVS measurement is rarely falsely low but there are several ways to get falsely high measurements. The first is that the cut through the IVS is oblique, rather than perpendicular. The second is that the RV moderator band inserts into the anteroseptum and may be included in the IVS measurement. Here is a good PLAX IVS measurement.

Here are the reference standards for the IVS.

 

Normal

Mild

Moderate

Severe

IV septum (cm)

0.6 - 1.1

1.2 - 1.3

1.4 - 1.6

≥1.7

The PSAX is rarely better than the PLAX for IVS measurement but if the view is good, be sure to measure in the basal inferoseptum to avoid the moderator band. The following PSAX shows the moderator band joining the anteroseptum.

Here is a PSAX IVS measurement in the inferoseptum.


 

Discrete upper septal thickening (DUST)/sigmoid septum/septal bulge/septal knuckle is relatively common, especially in older patients. It is associated with hypertension, but not hypertrophic cardiomyopathy, and should be less than 3 cm in length. Here is a diagram demonstrating the abnormality. The IVS measurement should be taken distal to this bulge but before the papillary muscles.

DUST is not completely cosmetic. It can cause turbulence in the outflow tract (resulting in a murmur) and hypovolemia or hyper-catecholamine states may cause temporary obstruction of the outflow tract with systolic anterior motion (SAM) of the anterior leaflet of the mitral valve. Thus, SAM is not specific to hypertrophic cardiomyopathy. Here is a clip from a patient with a modest septal bulge but without SAM.

 


The apical4 may show the IVS clearly, particularly when RV enhancement is used to get the beam more perpendicular to the IVS. In a true apical4 the view is through the inferoseptum, so the moderator band is avoided. However, lack of good endocardial resolution in this window, due to the ultrasound beam still being mostly parallel to the endocardium, may result in under measurement of the IVS. Here is an IVS measurement in an RV enhanced apical4.

The SC4 view may be excellent for the IVS because the ultrasound beam is more perpendicular to the IVS. Here is a subcostal IVS measurement. However, notice that the left ventricular outflow tract and the aortic valve are partly in view, making it possible that the cut is anterior enough to risk moderator band confounding.

The IVS is not measured in every view when it is clearly normal. But an abnormal width in any view should be validated in other views to avoid overcalling septal enlargement.


LV End Diastolic Diameter (LVEDD)

LVEDD varies with patient height and is measured at the same location and time as the IVS, measuring from endocardium to endocardium. It is important to carefully observe the live B-mode images to be clear where the chordal structures layer on top of the LV wall because the junction may be difficult to see in the end-diastolic frozen image. This can result in under measurement of LVEDD. Here is a PLAX LVEDD measurement.

Here is an RV enhanced apical4 LVEDD measurement.

As with the IVS measurement, a good SC4 may give the best LVEDD measurement because the ultrasound beam is perpendicular to the LV walls. Here is a normal LVEDD in the SC4/5.

The LVEDD assessment must consider the patient’s height. Compared to MR volume calculation, echocardiography tends to underestimate LV size, especially in women.

Left Ventricle

 

End Diastolic Diameter (cm)

3.8 - 5.8


LV FUNCTION

LV function is a complex mix of wall thickening, inward (radial) motion, longitudinal motion, rotatory motion, and active relaxation (diastolic function).

E-point septal separation (EPSS) in the PLAX is a traditional M-mode screening measurement for the LV that we no longer obtain routinely with Venue because we have better tools discussed later. EPSS assesses a combination of LV chamber size, diastolic function, left atrial pressure, and anterior mitral valve (MV) leaflet mobility. It measures the gap between the closest approach of the anterior mitral leaflet tip to the basal anteroseptum in early diastole. M-mode through the end of the leaflet best visualizes this gap because of the higher frame rate. This technique can also detect systolic anterior motion of the MV (SAM); we would obtain the EPSS tracing with Venue in patients with moderate or greater IVS enlargement or DUST. When it is difficult to get M-mode in-plane to the motion of the anterior leaflet toward the IVS, Venue has Anatomic M-mode that may get a more accurate measurement and the subcostal4 view may give better M-mode tracings across the MV and IVS.

Here is a normal EPSS tracing.

 

Normal

EPSS (cm)

0 - 0.7

Radial function (squeeze) is often visually assessed but this requires experience and an ability to integrate multiple views of the LV. Ejection fraction (EF) is typically measured during formal echocardiography by the Simpson biplane method. This requires tracings of the LV chamber in end systole and end diastole in both the apical4 and apical2 views. On Venue, an automated Simpson single-plane EF measurement (Real-time EF) can be made in the apical4. It requires an acceptable view of the LV with the endocardium of both walls in view throughout a cycle. The app indicates the quality of the view by the color of the outlined endocardium (we want green). Freeze the app at the end of expiration.

As compared to biplane EF (normal range 52-72% in men and 54-74% in women), the Real-time EF is an average of 3 percentage points lower with a 95% CI of +/- 10 percentage points. We typically add the 3% back to the Real-time EF for documentation to be synchronous with the biplane world. The CI is narrower with increasing quality of the imaging. Real-time EF with an acceptable or better apical4 is superior to fractional shortening and visual assessment by most physicians but it will be less accurate if LV wall motion abnormalities are present. EF is a popular measure, but it is not the full picture of LV function.

The Real-time EF application also calculates LV end-diastolic volume (LVEDV), which was on average about 14 mL lower than calculated manually by experts. The normal range for LVEDV is wide (106-214 mL in men and 86-178 in women) because it is body size dependent. Formal labs divide the raw value by body surface area to create an index, but we rarely have an accurate BSA available. We only use the LVEDV to follow select patients for change in LV chamber size (e.g., chronic MR and AR).

Longitudinal Systolic LV Function: Although longitudinal function comprises only about 10% of overall LV systolic function, it varies depending on the region of the LV and reduction in longitudinal LV function can be an early marker of various types of LV dysfunction. A special technique called speckle tracking is increasingly being used to determine longitudinal strain throughout cardiac chambers, but Venue does not currently have this capability. Mitral annular plane systolic excursion (MAPSE) with M-mode in the apical4 view is the traditional way to assess longitudinal function at the septal base of the heart, but this technique tends to give falsely high values and we rarely perform it with Venue. MAPSE measures the amplitude of the MV annular movement. There is a tissue Doppler measurement (s’, described just below) that we use with Venue instead of MAPSE, but it is helpful to understand MAPSE because it is still measured at other sites.

Understanding the location of the MV annulus is important for MAPSE and tissue Doppler imaging that is covered in the next section of this chapter. The annulus is a ring of fibrous tissue (a little more hyperechoic than myocardium) that supports the MV apparatus. On the screen, the septal part of the annulus in the apical4 view lies medial and a little apical to the base of the septal leaflet. It is not a particularly thick ring and is in continuity with the annulus of the aortic valve. The annulus lies vertically between the IVS and the interatrial septum and is passively moved by the myocardium in both chambers. The following drawing shows the location of the septal and lateral mitral annuli.

For MAPSE, the M-mode line needs to go through the septal annulus and be as in -plane as possible to the motion of the annulus. An optimized image of the annulus can be very important for difficult patients and anatomic M-mode may be needed to be in-plane. Position the cursor so it is best for end expiration, activate M-mode, and freeze at end expiration. Find the best complex towards the end of expiration and measure the difference between the peak and the valley of the annulus excursion. Longitudinal function usually decreases modestly with age, probably in concert with the development of diastolic dysfunction.

 

Normal

MAPSE (cm)

1.2 - 1.8


 

DOPPLER ANALYSIS OF LV FUNCTION

LV Inflow through the mitral valve can be measured with spectral Doppler to get the maximum velocity of the E-wave (early diastolic inflow caused by the suction/pull of active relaxation and the push of LA pressure) and the A-wave (late diastolic inflow from atrial contraction). These velocities are usually maximum near the tips of the open mitral valve leaflets at end expiration.

Step 1: Get an apical4 view with the IVS roughly vertical and both mitral valve leaflets in view.

Step 2: Color Doppler (Color) is activated, the sector box width is optimized for the LV inflow area, and the probe is then fanned “anterior/posterior” to find the plane with maximum intensity of the inflow signal (red flush) during expiration. Here is good red flush LV inflow signal along with blue LV outflow signal.

Step 3: Continuous wave Doppler (CW) is activated. CW measures velocity all along the line. The center of the line contains a “region of interest” which should be placed near the tips of the open mitral valve. This sharpens the tracing for this particular location. The best gate line position is usually a little lateral, rather than right in the center of the LV. This position also helps avoid the left ventricular outflow tract. Use the Color signal to get the gate line parallel to the strongest flow through the valve. Then, tap the CW button again to activate the tracing and do final angle correction as needed. The Baseline, complex size (Scale), or Sweep Speed may occasionally need adjusting with fingers or the Auto button. Don’t have more than 3-4 heart cycles per screen or important details may be missed. The active B-mode thumbnail in Venue (activated with the Simult button) and the Doppler sound can clarify where diastole begins. The tracing is frozen at the end of expiration and the complex with the maximum and clearest E wave is selected. Here is a normal tracing with the E and A waves measured (Venue calculates the E/A ratio).

E-wave velocities are usually 0.5 - 1.25 m/sec, but there are conditions with higher velocities (well hydrated athletic heart, mitral stenosis, mitral regurgitation, and decompensated heart failure). An important misleading cause of an elevated E wave is moderate or greater aortic regurgitation. In this condition, the complex hemodynamics in the LV may produce a sharp initial high E wave with a rapid decay and this E does not accurately reflect LAP. E-wave velocities less than 0.5 m/sec are either low cardiac index or poor gate positioning.

E-waves vary more than A-waves with changes in LA pressure and LV function, so the E/A ratio is dynamic. E, A, and E/A vary substantially with age. The following table shows the weighted mean values (m/sec) from a metanalysis of these values. The E velocity falls because LV diastolic function/suction usually decreases with age and the A velocity increases as there is more dependence on the atrial contraction to empty the increased residual volume in the left atrium.

LV Inflow

20 - 29 yr

30 - 39 yr

40 - 49 yr

50 - 59 yr

60 - 69 yr

70 - 79 yr

80 - 89 yr

E

0.83

0.78

0.73

0.67

0.67

0.66

0.64

A

0.45

0.51

0.55

0.61

0.71

0.78

0.90

E/A

1.91

1.56

1.37

1.16

0.99

0.87

0.73

Left atrial dysfunction: dysfunction of the left atrium with preserved sinus rhythm does occur. Both idiopathic heart failure with preserved ejection fraction and amyloidosis are reported to reduce atrial function without causing atrial fibrillation. This can decrease the A-wave velocity below what is expected for age, resulting in an increase in the E/A ratio.

Atrial fibrillation patients lack an A-wave, so all that can be measured is E. This measurement is useful, but the difficulty is the beat-to-beat variation in the E-wave. Multiple E-waves must be measured to accurately derive an average E-wave velocity. This is tedious, so the utility of IMBUS LV inflow analysis in an atrial fibrillation patient is only to quickly identify patients with very high E-wave velocities indicating one of the several conditions noted above.

PW LV Inflow analysis: The analysis is performed at some sites with PW, which measures just at the small gate, rather than along the whole line. Careful placement of the PW gate is essential. The gate line positioning steps described above for CW are still needed and the PW gate is carefully placed just past the tips of the open mitral valve. If the gate is too distal or proximal in the LV, lower velocities may be recorded so exploration with the gate in Duplex mode is often needed to be sure the maximum velocities are found.

In several published reports, CW measurements of E and A waves were about 10% higher than PW measurements and the IMBUS-COC experience supports this. A 2009 joint statement by the European and American echocardiographic societies noted, “CW to assess peak E and A velocities should be performed before applying the PW technique to ensure that maximal velocities are obtained.”

Tissue Doppler (TDI) analysis of the mitral annulus:  This measures the velocity of movement of the mitral annular tissue, including the positive s’ (longitudinal systolic function), negative e’ (active relaxation of diastolic function), and negative a’ (atrial contraction) waves. For PW TDI, the gate must be carefully placed in the center of the annulus and be parallel to its movement. The initial gate target is the septal mitral annulus, which on the screen means medial and a little apical to the base of the septal leaflet. However, the vertical gate position is also critical. If the gate is a little above or below the annulus, the waves change, almost always with a disproportionate reduction in the e’. This means that equivocal or low e’ values always need careful confirmation of correct gate placement. TDI analysis should probably not be performed on an atrial fibrillation patient. TDI should also not be done when there is significant mitral annular calcification, previous mitral valve repair or replacement, abnormal basal septal wall motion, significantly impaired right ventricular function, or ≥ moderate mitral regurgitation. TDI of the lateral mitral annulus avoids a few of these problems and we always use it to confirm low septal TDI measurements.

Step 1: Optimize the B-mode image of the mitral annulus. On Venue, the standard PW gate is first positioned over the mitral annulus for best location at end expiration, including the use of angle correction to be parallel to the motion of the annulus.

Step 2: After the gate is positioned, activate TDI. The complex size or sweep speed occasionally need adjustment with fingers. Freeze at the end of expiration and pick the complex with the largest, clearest e’ wave. A falsely high e’ is rare but it is easy to get a falsely low e’ with suboptimal gate placement. The s’, e’, and a’ peak velocities are measured. The following is a good TDI tracing with measurements.

The s’ is a better measure of longitudinal systolic LV function than MAPSE and is our standard with Venue. The s’ usually falls modestly with age but stays ≥ 0.07 unless some type of cardiac disease is occurring. The lateral mitral annulus s’ in middle-aged and elderly patients has the same ≥ 0.07 cutoff.

Traps: There is a part of LV contraction called isovolumetric contraction (IVc), which occurs in earliest systole when all valves are still closed. No change in LV volume occurs during this very brief event. The IVc can be seen in the TDI tracing above and is the initial brief up and down deflection right before s’. There is no IMBUS utility in measuring the usually small IVc peak or duration. However, the following TDI tracing demonstrates what can happen when the IVc velocity is higher than typical. The physician chose the IVc peak of 0.11 as s’, when the true s’ peak was about 0.06.

There is also a deflection after s’ and before e’ that can be seen in the two TDI tracings above. This is isovolumetric relaxation (IVr), occurring between aortic valve closure and mitral valve opening. Don’t confuse this deflection with e’. As with the E/A tracing, don’t have more than 3-4 heart cycles per screen or details may be missed.

The LV inflow section above noted that LA pressure changes affect E more than A. LA pressure only slightly affects e’ and a’ and the change is proportional in most patients. The a’ is our current best measure of LA function and it increases modestly with age as LV inflow becomes more dependent on atrial contraction. However, a’ can also decrease when left atrial function deteriorates, so the absolute velocity of a’ must be evaluated.

The table below is for the septal annulus. The lateral annulus e’ should be at least 0.03 m/sec higher than the septal (except in constrictive pericarditis) but lateral s’ and a’ should be about the same as the septal.

Mitral Annulus TDI

16 - 20 yr

21 - 40 yr

41 - 60 yr

> 60 yr

s’ (m/sec)

≥0.07

≥0.07

≥0.07

≥0.07

e’ (m/sec)

0.12 - 0.17

0.13 - 0.18

0.10 - 0.14

0.07 - 0.12

a’ (m/sec)
-- 0.07-0.10 0.08-0.12 0.09-0.12

LV OUTFLOW/CARDIAC INDEX: PW Doppler can assess the flow through the left ventricular outflow tract (LVOT). This flow is away from the probe, so the Doppler tracing is below the zero line as in the following tracing.

We need the area under the stroke curve, called the Velocity Time Integral (VTI), to estimate cardiac index. VTI (cm/stroke on Venue) varies with heart rate. The measurement can be false with moderate or greater severity aortic regurgitation or conditions with SAM.

Venue automates the tasks of obtaining the VTI with an app called Auto-VTI, which functions well with an acceptable or better apical5. The app places a region of interest (ROI) box over the distal LVOT and looks for a correct PW Doppler waveform, which includes laminarity of flow. The gate will not be at the valve where turbulent flow can occur. Following traditional manual echocardiography convention the app does not angle correct the PW gate. Therefore, the LVOT should be less than 30 degrees off-vertical to get accurate measurements. The app traces each stroke and recalculates every 2 seconds. The quality of the view is indicated by the color of the ROI box and when a green box occurs, freeze at end expiration to obtain the final output, as follows.

The app reports the VTI, HR, and a calculated surrogate of cardiac index called the CO Flux (VTI x HR)/1000) (the units don’t matter). CO Flux is independent of patient gender and size while correlating strongly with the standard body surface area corrected Cardiac Index. The average value for CO Flux is 1.5 and the normal range is from about 1.0 – 2.0. Patients below and above this range would be categorized as low and high cardiac index.


A NOTE ABOUT THE ATHLETES HEART:

This condition usually results from prolonged, intensive endurance training. The septum is rarely over 1.3 cm and both the right and left ventricles may be slightly above normal diameter. Radial LV function can appear low normal by eyeball and even by EF, but just having a patient squeeze a ball hard can improve the radial function. Specific LV longitudinal and diastolic function is normal to supra-normal in these athletes, eliminating the eyeball concern about reduced LV function.