ABC | Volume 110, Nº2, February 2018

Original Article Ferreira et al Alternative method to calculate simplified EOA proj Arq Bras Cardiol. 2018; 110(2):132-139 The aim of the present study is to measure the agreement between two methods of calculation of simplified EOA proj using two different approaches of flow rate determination in patients with classical LFLG AS. Methods Retrospective observational single-institution study that included all consecutive patients with LFLG AS with depressed LVEF (definition inaccordancewith the2014AHA/ACCGuidelines for the Management of Valvular Heart Disease 1 ) referred for DSE evaluation between September/2011 and November/2015. Patients admitted to the study had to fulfill all the following criteria: 1) age ≥ 18 years old; 2) EOA ≤ 1.0 cm 2 or EOA indexed to body surface area ≤ 0.6 cm 2 /m 2 and maximal transaortic velocity (Vmax) < 4 m/s or mean transaortic gradient (Gmean) < 40 mmHg and 3) LVEF < 50%. Patients with more than mild aortic regurgitation or more than mild mitral regurgitation or stenosis were excluded. After completing DSE, patients were classified into groups in terms of severity of the stenosis in agreement with the 2014 AHA/ACC Guidelines for the Management of Valvular Heart Disease: • Patients with true severe LFLG AS: EOA ≤ 1.0 cm 2 with Vmax ≥ 4 m/s at any flow rate • Patients who did not fulfill the criteria for true severe LFLG AS having: a) EOA ≤ 1.0 cm 2 with Vmax < 4m/s (persistent area – gradient mismatch), b) EOA > 1.0 cm 2 with Vmax ≥ 4 m/s or c) EOA > 1.0 cm 2 with Vmax < 4 m/s (pseudo-severe AS) Echocardiographic assessment Echocardiographic examination was performed using commercially available equipment (Vivid – 7; General Electric Vingmed, Milwaukee, WI) with a 3.5-MHz transducer. After the acquisition of the baseline study, a low dose dobutamine infusion protocol was begun at 5 ug/Kg body weight per minute, titrated upward in stages of 5 ug/Kg per minute every 5 minutes up to a maximal dose of 20 ug/Kg per minute. Systemic blood pressure and the 12-lead electrocardiogram were monitored throughout the test. Continuous wave Doppler of the aortic valve velocity spectrum and pulsed-wave Doppler of the LVOT velocity spectrumwere recorded at baseline and in the last 2 minutes of each stage of the protocol. LVOT diameter was measured in the basal parasternal long axis view and was assumed to have remained constant during the test protocol. Raw data was stored digitally and analysis was performed off-line by a single independent operator, using the EchoPac Clinical Workstation Software (General Electric, Vingmed, Milwaukee, WI). For each Doppler measurement, three cycles were averaged, avoiding post-extrasystolic beats. Transaortic gradients were calculated using the simplified Bernoulli equation ( ∆ P=4 ν 2 , where ΔP is in mmHg and v is the aortic velocity in m/s). EOA of the aortic valve was calculated from the continuity equation - EOA=CSA LVOT × (LVOT VTI ÷ Ao VTI ) -, where EOA is in cm 2 , LVOT VTI is the subaortic velocity -time integral and Ao VTI is the aortic velocity-time integral both in cm. CSA LVOT is the cross sectional area (in cm 2 ) of the LVOT calculated from the LVOT diameter measured in the parasternal long axis view (d in cm) assuming a circular geometry - CSA LVOT = π x (d/2) 2 . Left ventricular end diastolic and end systolic volumes (LVEDV and LVESV, respectively) and LVEF were assessed by standard 4 chamber and 2 chamber views using the biplane Simpson method. Stroke volume (SV) was calculated from the following equation: = LVOT VTI × CSA LVOT , where SV is in mL/beat, LVOT VTI is in cm and CSA LVOT is in cm 2 . Flow rate (Q) was calculated using 2 different methods: • a c l a s s i c a l m e t h o d u s i n g t h e f o r mu l a Q classic = 1000 × LVOT VTI × CSA LVOT TE , where Q classic is in mL/sec, LVOT VTI is in cm, CSA LVOT is in cm 2 and ET is the ejection time in ms measured in the continuous wave Doppler of the aortic valve velocity spectrum. 4 • an alternative method using the formula Q alternative = CSA LVOT × Vmean LVOT × 100, where Q alternative is in mL/sec, CSA LVOT is in cm 2 and Vmean LVOT is the mean velocity of blood in the LVOT during the ejection period in m/sec and is measured in the pulsed-wave Doppler of the LVOT velocity spectrum. 5 Patients with flow rate variation with dobutamine infusion ≥ |15|% in both classical and alternative methods were selected and simplified aortic valve area at 250 mL/s flow rate (EOA proj ) was calculated according to the formula published by Blais et al 4 : EOA proj = EOA basal + × (250 – Q basal ) ∆ EOA ∆ Q , where EOA proj is in cm 2 , Q is the mean transvalvular flow rate, EOA basal and Q basal are the EOA and Q at rest and ΔEOA and ΔQ are the absolute variation in EOA and Q with dobutamine infusion. 4 As we used two different methods to calculate flow rate we obtained two sets of values of simplified EOA proj in each eligible patient: 1) a classical simplified EOA proj using the classical method of flow rate calculation and 2) an alternative simplified EOA proj using the alternative method of flow rate calculation. Statistical analysis Categorical variables are described by frequencies and percentages. Continuous variables are presented as mean ± standard deviation. A scatter plot and a linear regression model were constructed to assess the strength of linear relation between the classic and the alternative methods of calculation of EOA proj and to quantify the proportion of variance that the two methods have in common. Finally, in order to evaluate the agreement between the two methods (i.e., how much the new method is likely to differ from the old), we built a Bland-Altman plot – a plot of the paired differences between the two methods against their mean. Normal distribution of the paired differences was verified by the use of Shapiro‑Wilk normality test. The bias was computed as the mean of the differences of the two methods. A one sample t test was conducted against the null hypothesis of no bias to evaluate the statistical significance of the calculated bias. Ninety‑five percent-limits of agreement were computed as the mean bias plus or minus 1.96 time its standard deviation. 6 Two-tailed p values < 0,05 were considered statistically significant. 133