Table shows baseline clinical and echocardiography variables in our patients. As expected, LV volumes were larger in patients with systolic HF. Again expectedly, LV mass was higher in Groups 2 and 3. In total, the numbers of data-points were as follows: 188 in Group 1, 69 in Group 2, and 36 in Group 3.
Baseline clinical and echocardiography data
There was a moderately strong correlation between mitral inflow E/A ratio and the E′/A′ ratio of the mitral annulus, (r = 0.60. P< 0.0001) as well as between s′ integral and mitral annulus E′ (r = 0.74, P< 0.0001) (Figure A and B). The correlation between mitral inflow E/A ratio and the E′/A′ ratio of the mitral annulus was lowest in the SHF group (r = 0.43, P = 0.0002) and highest in the HOCM group (r= 0.83, P< 0.0001). Also, the duration of early diastolic wave of the mitral inflow and of the mitral annulus (E and E′, respectively) strongly correlated (r = 0.89, P< 0.0001), with E-wave having a duration longer by 12 ± 26 ms (P< 0.0001). Similarly, duration of atrial wave of the mitral inflow and of the mitral annulus (A and A′, respectively) correlated (r = 0.75, P< 0.0001), but now with A-wave having a duration slightly shorter by −4 ± 21 ms (P = 0.001). Correlation between mitral annulus E′ and τ0 was significant, but weak (r = −0.19, P = 0.0005; Figure C).
Figure 2 (A) Correlation between the ratio of the peak early and late diastolic mitral inflow velocities (E/A ratio) and the ratio of the peak early and late diastolic velocities of the mitral annulus (E′/A′ ratio); (B) correlation between peak (more ...)
There was a strong correlation between the measured and predicted E′ (r = 0.90, P< 0.0001; Figure ). This correlation was marginally improved by adding τ0 as a predictor (multivariate r= 0.90; partial r for τ0−0.13, P= 0.03; Table ). When we repeated this analysis after separating the subjects into groups, τ0 was a weak independent predictor of E′ in normal subjects (partial r= −0.23, P= 0.001) but not in Group 2 (systolic HF patients), or Group 3 (HOCM patients) (Table ).
Correlation between measured peak early diastolic velocity of the mitral annulus (E′) and E′ predicted from the systolic displacement of the mitral annulus and the profile of the mitral inflow (predicted E′).
Estimating early diastolic velocity of the mitral annulus (E′) from predicted E′ and time constant of the isovolumic pressure decay (τ0) by multiple linear regression
Empirical approach to assessment of E′ predictors by multiple linear regression showed that the best overall predictor of E′ was s′ integral (P< 0.0001), followed by E/A ratio (P< 0.0001), with τ0 adding significantly but weakly to the model (partial r= −0.21, P= 0.0002). A mixed model that accounted for repeated measurements of the same subjects confirmed that the strongest E′ predictor was s′ integral (P< 0.0001), followed by E/A ratio (P< 0.0001), and τ0 (P= 0.0014). We then repeated this multiple linear regression approach in individual groups of subjects. In contrast to findings described in a previous paragraph, τ0 showed only a trend towards being a predictor of E′ in normal subjects (partial r= −0.10, P= 0.16). Again, τ0 was not a predictor of E′ in Group 2 (systolic HF patients) or Group 3 (HOCM patients) (Table ).
Table 3 Estimating early diastolic velocity of the mitral annulus from the integral of the systolic velocity of the mitral annulus (s′ integral), ratio of the early and late velocities of the mitral inflow (E/A ratio) and time constant of the isovolumic (more ...)
Inter- and intra-observer variability
The inter-observer variability for mitral valve E and A, and mitral annulus E′ and A′ velocities was 5 ± 6, 6 ± 7, 6 ± 8, and 7 ± 7%, respectively. The inter-observer variability for s′ wave integral, mitral E and A duration, and IVRT was 4 ± 5, 7 ± 5, 8 ± 6, and 10 ± 9%, respectively. Intra-observer variabilities were slightly lower (mitral valve E and A, and mitral annulus E′ and A′ velocities was 4 ± 6, 6 ± 6, 6 ± 7, and 7 ± 7%, respectively; s′ wave integral, mitral E and A duration, and IVRT was 3 ± 5, 6 ± 5, 8 ± 7, and 9 ± 9%, respectively).
The largest potential source of error in our study is the accuracy of our τ0
measurements. We have shown that our measurement of τ0
correlates strongly with τ0
measured using both Weiss and shifting asymptote method.18,11
However, to further estimate the maximal potential correlation between τ0
′ after adjusting for s
′ and E
ratio, we first subtracted the variance attributable to E
′ measurement from the residual sum of squares of multiple linear regression of E
′ predictors. Assuming that τ0
explained the entire residual sum of squares after this subtraction, its partial correlation coefficient was only −0.47, a value still not high enough for E
′ to be a clinically useful surrogate for τ0