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Comparison between cardiovascular magnetic resonance and transthoracic Doppler echocardiography for the estimation of effective orifice area in aortic stenosis.

Garcia J, Kadem L, Larose E, Clavel MA, Pibarot P - J Cardiovasc Magn Reson (2011)

Bottom Line: The intra- and inter- observer variability of TTE-derived EOA was 5 ± 5% and 9 ± 5%, respectively, compared to 2 ± 1% and 7 ± 5% for CMR-derived EOA.Underestimation of ALVOT by TTE is compensated by overestimation of VTILVOT, thereby resulting in a good concordance between TTE and CMR for estimation of aortic valve EOA.CMR was associated with less intra- and inter- observer measurement variability compared to TTE.

View Article: PubMed Central - HTML - PubMed

Affiliation: Québec Heart and Lung Institute, Laval University, Québec, Canada.

ABSTRACT

Background: The effective orifice area (EOA) estimated by transthoracic Doppler echocardiography (TTE) via the continuity equation is commonly used to determine the severity of aortic stenosis (AS). However, there are often discrepancies between TTE-derived EOA and invasive indices of stenosis, thus raising uncertainty about actual definite severity. Cardiovascular magnetic resonance (CMR) has emerged as an alternative method for non-invasive estimation of valve EOA. The objective of this study was to assess the concordance between TTE and CMR for the estimation of valve EOA.

Methods and results: 31 patients with mild to severe AS (EOA range: 0.72 to 1.73 cm2) and seven (7) healthy control subjects with normal transvalvular flow rate underwent TTE and velocity-encoded CMR. Valve EOA was calculated by the continuity equation. CMR revealed that the left ventricular outflow tract (LVOT) cross-section is typically oval and not circular. As a consequence, TTE underestimated the LVOT cross-sectional area (ALVOT, 3.84 ± 0.80 cm2) compared to CMR (4.78 ± 1.05 cm2). On the other hand, TTE overestimated the LVOT velocity-time integral (VTILVOT: 21 ± 4 vs. 15 ± 4 cm). Good concordance was observed between TTE and CMR for estimation of aortic jet VTI (61 ± 22 vs. 57 ± 20 cm). Overall, there was a good correlation and concordance between TTE-derived and CMR-derived EOAs (1.53 ± 0.67 vs. 1.59 ± 0.73 cm2, r = 0.92, bias = 0.06 ± 0.29 cm2). The intra- and inter- observer variability of TTE-derived EOA was 5 ± 5% and 9 ± 5%, respectively, compared to 2 ± 1% and 7 ± 5% for CMR-derived EOA.

Conclusion: Underestimation of ALVOT by TTE is compensated by overestimation of VTILVOT, thereby resulting in a good concordance between TTE and CMR for estimation of aortic valve EOA. CMR was associated with less intra- and inter- observer measurement variability compared to TTE. CMR provides a non-invasive and reliable alternative to Doppler-echocardiography for the quantification of AS severity.

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Flow velocity measurements in the left ventricular outflow tract by CMR. Panel A shows the change in peak left ventricular outflow tract (LVOT) velocity at -12 mm position during the cardiac cycle. Panel B shows the change in the instantaneous average velocity obtained over the region of interest. The velocity-time integral (VTI) is the area under the curve. Panel C shows the change in instantaneous flow (Q) calculated as follows: Q (t) = average velocity (t) × ALVOT, where ALVOT is the cross-sectional area of the LVOT. The stroke volume (SV) is the flow-time integral during systole. Panel D shows the change in peak aortic velocity at +6 mm position during the cardiac cycle, the velocity-time integral (VTI) is the area under the curve.
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Figure 3: Flow velocity measurements in the left ventricular outflow tract by CMR. Panel A shows the change in peak left ventricular outflow tract (LVOT) velocity at -12 mm position during the cardiac cycle. Panel B shows the change in the instantaneous average velocity obtained over the region of interest. The velocity-time integral (VTI) is the area under the curve. Panel C shows the change in instantaneous flow (Q) calculated as follows: Q (t) = average velocity (t) × ALVOT, where ALVOT is the cross-sectional area of the LVOT. The stroke volume (SV) is the flow-time integral during systole. Panel D shows the change in peak aortic velocity at +6 mm position during the cardiac cycle, the velocity-time integral (VTI) is the area under the curve.

Mentions: The peak and average flow velocities within the ROI were used to determine the changes in instantaneous peak (Vpeak, Figure 3A) and average (Vaverage, Figure 3B) velocity in the LVOT at the -12 mm position during the cardiac cycle. The velocity-time integral of Vaverage during systole was calculated (Figure 3B) and compared to the VTI measured by TTE in the LVOT. The instantaneous LVOT flow rate was calculated by multiplying the instantaneous Vaverage by the LVOT cross-sectional area, and the stroke volume (SVCMR) was calculated by using Simpson's rule to integrate flow during systole (Figure 3C).


Comparison between cardiovascular magnetic resonance and transthoracic Doppler echocardiography for the estimation of effective orifice area in aortic stenosis.

Garcia J, Kadem L, Larose E, Clavel MA, Pibarot P - J Cardiovasc Magn Reson (2011)

Flow velocity measurements in the left ventricular outflow tract by CMR. Panel A shows the change in peak left ventricular outflow tract (LVOT) velocity at -12 mm position during the cardiac cycle. Panel B shows the change in the instantaneous average velocity obtained over the region of interest. The velocity-time integral (VTI) is the area under the curve. Panel C shows the change in instantaneous flow (Q) calculated as follows: Q (t) = average velocity (t) × ALVOT, where ALVOT is the cross-sectional area of the LVOT. The stroke volume (SV) is the flow-time integral during systole. Panel D shows the change in peak aortic velocity at +6 mm position during the cardiac cycle, the velocity-time integral (VTI) is the area under the curve.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3108925&req=5

Figure 3: Flow velocity measurements in the left ventricular outflow tract by CMR. Panel A shows the change in peak left ventricular outflow tract (LVOT) velocity at -12 mm position during the cardiac cycle. Panel B shows the change in the instantaneous average velocity obtained over the region of interest. The velocity-time integral (VTI) is the area under the curve. Panel C shows the change in instantaneous flow (Q) calculated as follows: Q (t) = average velocity (t) × ALVOT, where ALVOT is the cross-sectional area of the LVOT. The stroke volume (SV) is the flow-time integral during systole. Panel D shows the change in peak aortic velocity at +6 mm position during the cardiac cycle, the velocity-time integral (VTI) is the area under the curve.
Mentions: The peak and average flow velocities within the ROI were used to determine the changes in instantaneous peak (Vpeak, Figure 3A) and average (Vaverage, Figure 3B) velocity in the LVOT at the -12 mm position during the cardiac cycle. The velocity-time integral of Vaverage during systole was calculated (Figure 3B) and compared to the VTI measured by TTE in the LVOT. The instantaneous LVOT flow rate was calculated by multiplying the instantaneous Vaverage by the LVOT cross-sectional area, and the stroke volume (SVCMR) was calculated by using Simpson's rule to integrate flow during systole (Figure 3C).

Bottom Line: The intra- and inter- observer variability of TTE-derived EOA was 5 ± 5% and 9 ± 5%, respectively, compared to 2 ± 1% and 7 ± 5% for CMR-derived EOA.Underestimation of ALVOT by TTE is compensated by overestimation of VTILVOT, thereby resulting in a good concordance between TTE and CMR for estimation of aortic valve EOA.CMR was associated with less intra- and inter- observer measurement variability compared to TTE.

View Article: PubMed Central - HTML - PubMed

Affiliation: Québec Heart and Lung Institute, Laval University, Québec, Canada.

ABSTRACT

Background: The effective orifice area (EOA) estimated by transthoracic Doppler echocardiography (TTE) via the continuity equation is commonly used to determine the severity of aortic stenosis (AS). However, there are often discrepancies between TTE-derived EOA and invasive indices of stenosis, thus raising uncertainty about actual definite severity. Cardiovascular magnetic resonance (CMR) has emerged as an alternative method for non-invasive estimation of valve EOA. The objective of this study was to assess the concordance between TTE and CMR for the estimation of valve EOA.

Methods and results: 31 patients with mild to severe AS (EOA range: 0.72 to 1.73 cm2) and seven (7) healthy control subjects with normal transvalvular flow rate underwent TTE and velocity-encoded CMR. Valve EOA was calculated by the continuity equation. CMR revealed that the left ventricular outflow tract (LVOT) cross-section is typically oval and not circular. As a consequence, TTE underestimated the LVOT cross-sectional area (ALVOT, 3.84 ± 0.80 cm2) compared to CMR (4.78 ± 1.05 cm2). On the other hand, TTE overestimated the LVOT velocity-time integral (VTILVOT: 21 ± 4 vs. 15 ± 4 cm). Good concordance was observed between TTE and CMR for estimation of aortic jet VTI (61 ± 22 vs. 57 ± 20 cm). Overall, there was a good correlation and concordance between TTE-derived and CMR-derived EOAs (1.53 ± 0.67 vs. 1.59 ± 0.73 cm2, r = 0.92, bias = 0.06 ± 0.29 cm2). The intra- and inter- observer variability of TTE-derived EOA was 5 ± 5% and 9 ± 5%, respectively, compared to 2 ± 1% and 7 ± 5% for CMR-derived EOA.

Conclusion: Underestimation of ALVOT by TTE is compensated by overestimation of VTILVOT, thereby resulting in a good concordance between TTE and CMR for estimation of aortic valve EOA. CMR was associated with less intra- and inter- observer measurement variability compared to TTE. CMR provides a non-invasive and reliable alternative to Doppler-echocardiography for the quantification of AS severity.

Show MeSH
Related in: MedlinePlus