Echocardiography II - Part 2. Flashcards
The velocity of the image is being recorded at 0.6 m/s. (1) By what technique could you use to establish a VTI and (2) what does the VTI mean?
(1) Trace the flow profile provides the velocity time intergral (VTI)/Flow velocity integral (FVI). This could be done manually or by the machine.
(2) VTI/FVI measures the mean velocity throughout the flow period. The peak velocity is automatically calculate within the flow trace.
What information does the flow velocity integral (FVI)/velocity time intergral (VTI) provide?
Flow integral is calculated by tracing the flow profile. Once the entire flow profile is traced, the VTI is displayed on the monitor in cm. The area under the flow velocity curve represents the distance a volume of blood travels.
As the VTI is directly proportional to the stroke volume, this information together with the area of a vessel or the valve of blood is flowing through can calculate the stroke volume
What primary vessels can systolic time intervals be measured from?
Aortic (LVOT) and pulmonary (RVOT) flow profiles.
What is the acceleration time (AT) of a flow profile?
(AT) is the time to peak flow measured from the onset of flow to the point of maximal velocity. This is typically measured at the baseline.
What is the ejection time (ET) of a flow profile?
(ET) is the time measured from the onset of flow to the end of flow at the baseline.
Obtaining the AT from the RVOT and LVOT [RVAT and LVAT, respectively] may be divided by the ET. What information does this provide?
These two systolic time periods are then divided to yield a variable that indicates what fraction of time is spent in reaching maximal velocity (AT/ET).
When would you measure the pre-ejection period (PEP)?
(PEP) is measured from the onset of the QRS complex to the onset of the systolic flow.
Here continuous wave aortic flow is used to measure ejection time (LVET) from the onset of flow to the end of flow at the baseline and pre-ejection period (PEP) from the start of the QRS complex to the beginning of aortic flow. A ratio, LVPEP/ET, is then calculated.
Define the isovolumetric relaxation time (IVRT) period.
The time interval from cessation of aortic flow to the beginning of transmitral flow
Where would you optimally measure the IVRT?
The isovolumic relaxation time (IVRT) is measured by placing a CW or PW signal in the left ventricular outflow tract on apical four or five chamber imaging planes near the mitral valve and recording part of both the aortic flow profile and the transmitral flow profile.
Describe the typical appearance of aortic flow profiles.
Aortic flow profiles are negative and have rapid acceleration compared to the slower deceleration rate.
Therefore, this gives the normal aortic flow profile an asymmetric appearance
What factors may affect peak aortic velocity?
Factors that may increase aortic peak velocity:
1. Sympathetic stimulation
2. High left ventriuclar preload
3. low heart rate
4. low blood viscosity
5. Certain drugs (e.g., inotropes, arterial vasodilators)
6. Noise stimuli as stress factors.
Factors that may decrease aortic peak velocity:
1. Negative inotropes (e.g., administration of β‐blockers)
2. Systolic dysfunction
3. Tachyarrhythmias
4. Dehydration
Measurement of the aortic flow is particularly relevant in some breeds predisposed to aortic stenosis, like the Boxer. What is a generally accepted normal value for peak aortic velocities? what is generally considered abnormal? what is considered equivocal? What about a Boxer with with a measured aortic velocity of 2.56 m/s?
Most normal healthy dogs have aortic flow velocities less than 2 m/s.
There is agreement that flows above 2.5 m/s are abnormal
Flows within the 2 to 2.5 m/s range are equivocal.
Aortic peak velocity values of up to 2.56 m/s are measured in Boxers in the absence of any evidence of discrete lesions in the LVOT by both transoesophageal and transthoracic echocardiography. Boxers may also have smaller LVOT areas compared with other breeds.
Describe the typical appearance of pulmonic flow profiles.
Pulmonary artery flow profiles are negative in all the views that can be obtained in small animals
The normal pulmonary flow profile has a very symmetrical shape with similar acceleration and deceleration rates.
Often it displays a rounded peak as opposed to the pointed peak velocity of aortic flow.
What factors may affect pulmonary flow velocity?
- Respiration affects flow within the right side of the heart. Therefore, increased venous return with inspiration increases pulmonary flow during inspiration.
- Heart rate. Fast heart rates in the dogs increase velocities.
What is a generally accepted normal value for peak pulmonary velocities?
Peak pulmonary flow velocity in the dog is typically less than 1.3 m/s in many studies. \
Normal pulmonic flow has lower velocity than aortic flow because of lower resistance within the pulmonary vascular system.
What is a generally accepted AT/ET (acceleration time to total ejection time) for pulmonary velocities? When is peak velocity typically reached during ejection period?
Pulmonary flow has a slightly longer ejection time and a reduced pre-ejection period compared to aortic flow because of the reduced afterload.
- AT/ET = 0.43
- Halfway
Describe the different types of pulmonary flow patterns which may be observed that can raise suspicion for pulmonary hypertension?
(A) Dome-like pulmonary artery (PA) flow in a normal dog.
(B) Sharp peak appearance of pulmonary artery flow in a dog with increased systolic PA pressure.
(C) Notched pulmonary artery flow in a dog with severely increased systolic PA pressure.
In dogs with pulmonary hypertension (B and C) there is a short flow acceleration time causing the pulmonary artery flow to resemble an aortic flow pattern as the peak velocity is reached sooner and the flow becomes asymmetric. The notch in the flow in image C is caused by flow reversal during the deceleration phase.
Systolic notching and an abnormally low AT/ET of less than 0.30 are some of the criteria evaluated to diagnose probability of pulmonary hypertension.
What is a more accurate indicator of left ventricular function, that factors out the effects of heart rate?
The pre-ejection time period (PEP) is very similar to the isovolumic contraction period where both the aortic and mitral valves are closed, and the ventricle is building up enough pressure to open the aortic valve.
A ratio of PEP to LVET is usually calculated to reduce the effects of heart rate on LVET. This is considered a more accurate indicator of left ventricular function. Reference ranges might vary slightly with breeds, however a ratio of less than 0.45 is usually considered normal.
When heart rates are variable, how do we measure systolic time intervals.
Time intervals measured from the longest cardiac cycles tend to be the most accurate indicators of left ventricular function when heart rates are variable. Avoid measuring during ventricular or supraventricular premature complexes or the beats that follow them.
Describe the typical appearance of transmitral flow profiles.
Transmitral valve flow profiles in all planes are positive, and when heart rates are slow enough, the two phases of left ventricular filling are well separated.
Once heart rates exceed approximately 125 beats per minute (bpm), the two phases begin to overlap and rates greater than 200 bpm show no separation of filling phases.
The E peak (rapid ventricular filling) should have a higher velocity than the A peak in the normal heart. The E:A ratio is greater than one in the normal canine heart, but both slow heart rates and high heart rates can decrease this.
What factors tend to affect transmitral flow?
Transmitral flow is affected by preload, myocardial relaxation, and heart rate.
How does slow heart rates affect transmitral flow?
Slow heart rates have increased A flow velocity due to increased volume associated with the atrial contraction, minimising the difference in E and A velocities.
How does high heart rates affect transmitral flow?
Rapid heart rates decrease the E velocity secondary to decreased early ventricular filling volume and increased flow associated with the atrial contraction.
What is MV Deceleration time (MV DecT)?
Deceleration time after rapid ventricular filling is the time from the point of maximal E velocity along its deceleration slope to the baseline (from the E wave the slope of the E wave is traced to the baseline). Calculations are automatically performed by the machine tracing the slope.
What factors influence the peak filling rate and MV flow deceleration in ventricular diastole?
- Isovolumic relaxation –> affects EARLY diastolic ventricular filling.
- Pressure gradient from LA to LV
- Ventricular compliance –> affects LATE diastolic ventricular filling.
What are some factors that INCREASE E-wave velocities?
- Increased LA pressure
- Decreased LV pressure secondary to increased rate of relaxation
- Decreased LV compliance
- Small MV Area
What are some factors that DECREASE E-wave velocities?
- Low LA pressure
- Decreased rate of relaxation
- Increased LV compliance.
- Large MV area
What are some changes observed in older dogs, with regards to MV flow profiles?
- E wave velocity decreases and A wave velocity increases
- E:A ratio decreases as a result
- E deceleration time increases –> influenced by body weight and heart rate
What is a large factor affecting E:A wave when assess transtricuspid flow velocities.
Respiration.
Peak tricuspid E wave velocity varies with respiration. Inspiration increases peak flow velocity while expiration decreases E flow velocities. The E:A ratio therefore increases with inspiration and decreases with expiration. The ratio can even be less than one under appropriate conditions in a normal heart.
Describe the flow profile with pulmonary venous flow (PVF)?
Pulmonary venous flow is continuous and phasic into the left atrial chamber.
Left atrial filling occurs predominantly during ventricular systole when the mitral valve is closed. The velocity of this systolic flow is directly related to mean left atrial pressure. During ventricular diastole when the mitral valve is open, blood flow into the left atrium is directly related to flow moving into the left ventricle and occurs at the same time as early transmitral valve flow (E wave). During atrial contraction there is reverse flow into the pulmonary veins called atrial reverse (Ar).
Atrial reverse occurs during the atrial contraction (A-wave) phase of diastole. What factors may affect atrial reverse?
- End-Diastolic LA pressure.
- LA function
- LV compliance
- Heart rate and rhythm.
NO QUESTION: The following is a graph of LV diastolic function in cats.
And again..
What does a LAA flow velocity of (<0.25 m/s) typically indicate.
Stasis of blood flow is associated with lower than normal auricular flow and predisposition toward thrombus formation. At these pressure, the patient is at increased risk of spontaneous echocardiographic contrast and possible thromboembolism.
What are the effects of preload, afterload and HR on systolic time intervals
What are the effects of various cardiac diseases on systolic time intervals
How can you obtain stroke volume during a routine echocardiogram examination, without the machine giving you the values?
VTI is directly proportional to stroke volume. VTI is multiplied by the area of the vessel, valve, or orifice, through which flow volume is being calculated to obtain the stroke volume through that path in the heart.
This measurement can be done at any of the four valves. Flow velocity integrals at the mitral valve should use profiles that maximize peak E and A velocities.
Increases in FVI may suggest increased volume (as in a shunt).
Decreases in FVI can represent poor flow.
Define the Tei/mpi Index.
The TEI or myocardial performance index (MPI) is an index of global myocardial function and includes both diastolic and systolic time intervals.
This measurement uses ventricular ejection time and the isovolumic periods (contraction IVCT and relaxation IVRT) to derive an overall assessment of global ventricular function. MPI (Tei Index) assesses global ventricular function using PW Doppler or TDI.
LV MPI = (IVRT + IVCT) / LVET = MCO - LVET / LVET
RV MPI = (IVRT + IVCT) / RVET = TCO - RVET / RVET
Where LV is left ventricle, RV is right ventricle, IVRT is isovolumic relaxation time, IVCT is isovolumic contraction time, MCO is mitral valve closing to opening time, TCO is tricuspid valve closure to opening time, and LVET and RVET are left and right ventricular ejection times, respectively.
Describe how TEI/MPI index can be used using tissue Doppler evaluation.
Myocardial performance index can also be calculated using tissue Doppler evaluation of the longitudinal free wall or septum on apical four-chamber views of the heart. The advantage to deriving the MPI using TDI is that the same cardiac cycle can be used since TDI records myocardial motion during systole and diastole wherever the pulsed-wave gate is placed. Tissue Doppler MPI may help overcome errors in evaluation secondary to variations in heart rate when PW is used at different points in time.
Intervals used for the calculation of the MPI using Tissue Doppler: IVRT= isovolumic relaxation time, IVCT = isovolumic contraction time, ET = left ventricular ejection time, S′ = systolic myocardial motion, E′ = early diastolic myocardial motion, A′ = late diastolic myocardial motion.
Like the 4-types of values that Tissue Doppler can acquire when measuring for systolic myocardial function.
Tissue Doppler time intervals associated with systolic myocardial function include:
- Q–S’ (the time interval from the beginning of the QRS complex to the beginning of S’)
- Q–peak S’ (the time interval from the beginning of the QRS complex to peak velocity of S’)
- Q–end S’ (the time interval from the beginning of the QRS complex to the end of S’)
- Duration of S’
There are significant INVERSE relationships between Q–S’ and ejection fraction and between Q–end S’ and ejection fraction, and a significant POSITIVE relationship between ejection fraction and duration of S’.
NOTE: These TDI indices are heart rate affected, and all of these time intervals should be corrected for heart rate (dividing the parameter by the square root of the R-to-R interval).
List parameters to assess diastolic function.
- Isovolumetric relaxation time
- Pulmonary vein flow
- transmitral valve flow
- TDI - E’ and A’
Describe the IMPAIRED relaxation pattern, in the assessment of diastolic function.
With early diastolic dysfunction there is less passive filling and the E wave becomes smaller than the A wave; this is termed impaired relaxation. This can be normal in elderly patients.
It is characterized by:
- Reverse E:A ratio (<1)
- Slow MV deceleration
- Long IVRT
Describe the PSEUDONORMAL relaxation pattern, in the assessment of diastolic function.
As diastolic function worsens the left atrial pressure increases and the E wave once more becomes taller than the A wave. This is called pseudonormal filling, as the E:A ratio is normal/looks normal, however significant diastolic dysfunction is present.
Normal and pseudonormal filling cannot be distinguished on transmitral flow alone and TDI and pulmonary venous flow are often needed to define the pattern.
Describe the RESTRICTIVE relaxation pattern, in the assessment of diastolic function.
Finally in severe diastolic dysfunction the markedly elevated LA pressures result in fast, short early filling. The A wave is small, reflecting the fact that most filling is achieved by the E wave. LA function is often reduced as well, which contributes to the small A wave. This is called restrictive filling. The E:A ratio in restrictive filling is greater than 2.
