ECHOCARDIOGRAPHIC ASSESSMENT OF DIASTOLIC DYSFUNCTION FOR MEDICAL STUDENTS
Questions that will be answered:
What is diastolic dysfunction?
What is Diastolic Heart Failure?
What are we measuring in the echo?
Where are we measuring it in the echo?
What do the measurements mean?
And, when can we diagnose Diastolic Heart Failure?
INTRODUCTION / DEFINING OUR TERMS / DIASTOLIC HEART FAILURE OVERVIEW
Exposure to echocardiography for medical students and physician assistant students is limited at best, and when the exposures do occur, the level of discussion generally seems to skip the first few important lessons regarding ultrasound and echocardiography. This presentation is meant to breakdown what we are measuring to evaluate diastolic dysfunction specifically. We will also offer some specifics regarding diagnosis that may not be crucial for students to memorize but will help us specifically define diastolic dysfunction as it pertains to diastolic heart failure.
Speaking of defining things, let’s define some terms so we can speak accurately and precisely about our subject matter.
Heart Failure: inability of the heart to provide sufficient forward output to meet perfusion and oxygenation requirements of tissues. This can be subdivided into:
Systolic Heart Failure: impaired contractile function of the heart characterized by decreased left ventricular function, progressive chamber dilation, and eccentric remodeling. Values for left ventricular ejection fractions warranting diagnosis of SHF vary. Most agree that below 35-50% constitutes SHF. Classically the definition has been LVEF < 35%, but evidence is mounting that definition should include patients with LVEF < 50%.
Diastolic Heart Failure: abnormal ventricular relaxation, stiffness, or filling in the setting of normal left ventricular ejection fraction, left ventricular end diastolic volume, and signs/symptoms of heart failure.
Necessary for diagnosis:
—Signs/symptoms of heart failure
—Preserved Ejection Fraction (>50%)
It is worth noting that these are distinct entities with separate pathophysiologic mechanisms and features. These disorders are not part of a contiguous spectrum of disease. Conversion from diastolic heart failure and systolic heart failure generally does not take place unless some injurious incident such as myocardial infarction occurs.
Next, we need to make the distinction between diastolic heart failure and diastolic dysfunction. These terms are not interchangeable.
Diastolic Dysfunction: functional abnormality of diastolic relaxation, filling, or distensibility of the left ventricle irrespective of left ventricular ejection fraction.
—refers to mechanical properties of left ventricle
—does not refer to the patient’s presentation
—diastolic dysfunction can be present without diastolic heart failure
We will more extensively characterize diastolic dysfunction later on with ultrasound.
Speaking of Ejection Fraction, here are generally agreed upon ranges:
—Two StdDev below mean: 50-55%
—Greater than 35% is often referred to as preserved
These next few are a little more esoteric and not as crucial to remember:
Heart Failure with Reduced Ejection Fraction: the same as systolic heart failure; can be used interchangeably
Heart Failure with Preserved Ejection Fraction (>35%): used to define patients with LVEF between 35 and 50 percent. This term is NOT interchangeable with diastolic heart failure. This term was created because research was being targeted to optimize treatment of patients that fall within the LVEF 35-50% range. There was success in treating this patient population just as patients with LVEF < 35% are treated. So, perhaps patients with the diagnosis of heart failure with preserved ejection fraction should be absorbed into the systolic heart failure population. Additionally, perhaps the definition of systolic heart failure should apply to patients with LVEF < 50% as opposed to LVEF < 35%.
STAGES OF DIASTOLE
Quickly, here’s a run-through of the stages of diastole:
—Isovolumetric relaxation of LV; aortic and mitral valves closed
—Early LV filling; mitral valve open
—Mid diastolic phase
—Late filling with left atrial contraction
ECHOCARDIOGRAPHY AND DIASTOLIC DYSFUNCTION
And now for something a little different. Let’s go on to evaluate diastolic dysfunction, which is only one part of our criteria for diastolic heart failure. We are obviously using echo for our assessment. Our focus from here on out is only diastolic dysfunction.
We will be using specific measurements from primarily the apical four chamber view. These specific measurements will give us clues as to factors that characterize diastolic dysfunction such as:
—Left Ventricular Hypertrophy / Thickness
—Left Ventricular Volume
—Left Atrial Enlargement / Volume
—Elevated Pulmonary Artery Pressure
—Elevated Left Atrial Pressure
We will use 4 distinct methods, so to speak, to generate our specific measurements to give us clues as to the presence of the indicators that characterize diastolic dysfunction.
- Transmitral Doppler Inflow Velocity
Essentially measuring the velocity of blood flow across the mitral valve.
- Pulmonary Venous Flow
Again, measuring velocity of blood as it flows from pulmonary vein to left atrium.
- Tissue Doppler Imaging
This one is a little different. We are still measuring velocity, but we are measuring the velocity of the medial and lateral aspects of the mitral annulus as it moves during the cardiac cycle.
- Color Flow Mapping
Real-time view of inflow of blood into the left ventricle.
TRANSMITRAL DOPPLER INFLOW VELOCITY
The idea is that during diastole, blood flows across the mitral valve in two waves. The early wave (denoted as E) is created by the large discrepancy in pressures between the left atrium and left ventricle. The pressure is low in the LV. When the mitral valve opens, there is an initial rush of blood into a receptive LV, if you will. The second wave (denoted as A for atrial) is created by atrial contraction that generally sends a less forceful flow of blood across the mitral valve in the heart.
We make our measurements in the four chamber apical view. We place a 1-2 mm pulsed wave (PW) Doppler sample volume at the level of the tips of the mitral leaflets.
Image 1 – Apical Four Chamber View
In a healthy heart, the peak of the E wave (indicating maximum velocity of the early flow) is greater than the peak of the A wave. A normal E/A ratio is generally between 1 and 2, some sources say between 0.75 and 1.5.
The flatter region between each wave is called the diastasis.
Image 2 – Transmitral Velocity Waveforms – Normal
Here is another:
Image 3 – Transmitral Velocity Waveforms # 2 – Normal
As a quick aside at this point, the Y-axis for these graphs represents velocity in meters or centimeters per second and the X-axis represents time. This means that any positive deflection indicates forward blood flow and negative deflections indicate backward flow.
In the presence of diastolic dysfunction, the E wave peak is less than the A wave peak because the left ventricle is not as receptive. Or, put another way, pressure in the LV during early filling is too high, therefore the pressure gradient between the LA and LV when the mitral valve opens is not as great resulting in decreased early blood flow velocity across the mitral valve, which is represented as a smaller E wave. In this case, the atrial contraction picks up the slack, so the peak velocity across the valve is greater. This is known as E-A reversal and we get this sort of graph:
Image 3 – Transmitral Velocity Waveforms Demonstrating E-A Reversal
In addition to the E/A ratio for the transmitral Doppler inflow velocity, we also measure deceleration time. Deceleration time is measured as the time from the peak velocity to the return to baseline. This is better represented in this image
Image 4 – Transmitral Velocity Waveforms of Diastolic Dysfunction Grades
A normal deceleration time (Dt) is generally between 140 and 220 milliseconds.
Image 5 – Transmitral Velocity Waveforms with Deceleration Time Measurement
Based on these findings, we can classify certain patterns of abnormal mitral inflow.
- Impaired Left Ventricular Relaxation Pattern
—The isovolumetric relaxation time of the left ventricle is increased; ie: it takes longer to relax.
—E/A ratio < 1
—Dt > 220 ms (prolonged)
—Can be caused by HTN, CAD, CM in the presence of normal filling pressures
- Pseudonormal Pattern
—In the setting of increased left atrial pressures with impaired LV relaxation.
—E/A ratio is between 1 and 2 (hence, pseudonormal)
—Dt > 140
—Valsal va maneuver during echo can revert this to impaired relaxation pattern due to the brief reduction in venous return to left atrium and left atrial pressure.
—The parameters of mitral valve flow appear relatively normal, but other measurements can give clues as to diastolic dysfunction.
- Restrictive Filling Pattern
—In the setting of dramatically elevated left atrial pressures
—E/A > 2
—Dt < 150 ms
PULMONARY VENOUS FLOW
The principles are similar in comparison to the transmitral Doppler inflow measurements; the region of interest is different, and the pattern of flow is different.
For these measurements, we are again in the apical four chamber view. We place our sample volume 1-2 cm into the right pulmonary vein. We again use pulse wave Doppler. Color Doppler can be used for better visualization initially to localize the sample volume to the pulmonary vein’s flow into the left atrium.
Three velocities are measured generating three waves:
- Initial forward systolic flow (S) – related to left atrial relaxation and LV systolic contraction with mitral annular descent to apex.
- Forward flow from veins into Left Atrium during diastole (D)
- Retrograde flow from Left Atrium into pulmonary veins during atrial systole (Ar)
Image 6 – Pulmonary Venous Flow Waveform – Normal
The D wave is normally equal to or smaller than the S wave. An Ar amplitude > 25 cm/s suggests LA pressure > 20 mmHg. We can also calculate the Systolic Filling Fraction (SFF), which is equal to: S / (S + D). An SFF < 40% suggests increased LA pressures as well.
Limitations to using pulmonary venous flow include mitral valve disease, heart block, tachycardia, and pericardial compression syndromes.
The big picture is that all of these measurements from the echo are being used to suggest increased left atrial pressure, which is one of our indicators for diastolic dysfunction.
TISSUE DOPPLER IMAGING
At this point, we shift our focus in what we are measuring. Instead of blood flow, we are measuring mitral annulus motion. We are still measuring velocity.
Technically, we are measuring Doppler shifts caused by myocardial motion. We can assess the function of segmental regions of myocardium, and we can assess global cardiac function. In this instance, the myocardial motion will give insight to left ventricular filling pressures. This discussion will only focus on the parameters assessing global function.
In normal function, the mitral valve annulus descends toward the apex during systole. During diastole, it recoils back toward the base of the heart in early (e’) and late (a’) diastole. Similar to the E and A waves, two waveforms are generated from the velocity measurements from this characteristic motion. The systolic waveform is labeled “ s’ ”.
Image 7 – Mitral Annulus Velocity Waveform – Normal
The positive deflection in this graph represents motion towards the apex. The e’ and a’ waveforms of interest are seen in the negative deflection. We can measure the amplitude at the peak of each waveform to find the peak velocity.
We are once again in the four chamber apical view. We make measurements at two areas of interest: the medial and lateral (septal) mitral annulus. The following example shows the marker at the medial aspect of the annulus.
Image 8 – Apical Four Chamber View Demonstrating Position of M-mode Scan Line for Tissue Doppler Imaging (Medial aka Septal Annulus position shown)
From these measurements, we use the “E” value measured during the mitral valve flow study to calculate two E/e’ ratios, one for e’(lateral) and one for e’(medial). The E/e’ ratio can give indications as to left atrial pressures.
Normal e’ velocities from the lateral mitral annulus (15 cm/sec) are higher than those from the media annulus.
An E/e’(medial) ratio < 8 suggests normal left atrial pressure.
An E/e’(lateral) ratio < 5 suggests normal left atrial pressure
An E/e’(medial) ratio >12 and E/e’(lateral) > 10 suggest elevated left atrial pressure or pulmonary capillary wedge pressure (>18 mmHg)
COLOR FLOW MAPPING
We are switching gears back to monitoring blood flow. The color M-mode provides direct visualization of blood inflow into the left ventricle. We can make a measurement called Velocity propagation to assess left ventricular relaxation, which can help distinguish patients with pseudonormal filling from those with normal LV relaxation.
Again, we’re in the four chamber apical view. We use the M-mode scan line through the center of the column of left ventricular inflow.
In words, the velocity propagation is the slope of the first rising velocity during early filling measured from the mitral valve plane to 4 cm apically in the left ventricle. Put more simply, it is the slope of the transition from color to no color.
Image 9 – Velocity Propagation Measurement for Color Flow Mapping
A Velocity propagation (Vp) > 50 cm/s is considered normal.
Table 1 – Diastolic Dysfunction Echocardiographic Assessment Methodologies
||Sample Volume Region
||A4C or A2C
||Between tips of mitral leaflets
||Pulse wave Doppler
|↑ LA pressure
↑ LV pressure
↓ LV relaxation
|Measures velocity of blood flow across mitral valve to evaluate LA and LV pressures
|Pulmonary Venous Flow
||1-2 cm into R upper pulmonary Vein
||Pulse wave Doppler
|S, D, Ar
Systolic Function Fraction
|↑ LA pressure
||Measures velocity of blood flow from PV to LA to evaluate LA pressure
|Tissue Doppler Imaging
||Medial (septal) and lateral border of mitral annulus
||Pulse wave Doppler
|↑ LA pressure
||Measures velocity of medial/lateral mitral annulus recoil to evaluate LA pressure
||Center of LV inflow column
||Pulse wave Doppler
||↓ LV relaxation
||Measures velocity propagation at LV inflow column to evaluate degree of LV relaxation.
Table 2 – Diastolic Dysfunction Grading System by the Numbers
||Deceleration time (Dt)
Normal filling pressures
|< 1 (↓)
||>240 ms (↑)
||< 8 (Normal)
||< 5 (Normal)
Elevated filling pressures
|< 1 (↓)
||>240 ms (↑)
||> 15 (↑)
||> 10 (↑)
|1 < E/A < 2 (Normal)
||140 ms < Dt < 220 ms
|> 15 (↑)
||> 10 (↑)
||Ar > 25 cm/sec
Dramatically elevated LA pressures
|> 2 (↑)
||< 160 ms
||> 15 (↑)
||> 10 (↑)
Table 3 – Markers of Elevated Left Ventricular Filling Pressures
|> 2 (↑)
Deceleration Time (Dt)
|< 160 ms
Pulmonary Flow S/D
Left Atrial Enlargement
Left Ventricular Hypertrophy
Using these four modalities we were able to generate values and calculations that provided insight into atrial and ventricular pressures and volumes, which can be indicators of diastolic dysfunction. Looking at the big picture again, diastolic dysfunction determined from echocardiography is only one of the components of diastolic heart failure, but it is certainly a crucial component.