Statistical analysis
Epi Info version 7.1.1 software was used for the analysis of the data.
Continuous data were presented as mean with standard deviation and
compared by t-test. Continuous data of more than two groups were
compared by ANOVA test. Categorical data were presented as frequency and
percentage and compared using a chi-square test. P value <0.05
was considered as significant. To investigate for inter-observer
variability for LA strain, analysis of 10 random subjects was done by
two independent investigators who were blinded to the clinical data. For
intra-observer variability, repeat offline LA strain estimation was done
at 5 ± 2 days later in 10 randomly selected patients. The interclass
correlation coefficients (ICCs) were calculated with point estimates and
95% confidence intervals (CIs) being reported.
Results
We enrolled 120 subjects including 80 cases and 40 controls in our
study. There were 57 females and 23 males amongst cases while among
control population there were 15 females and 25 males. Table 1 shows the
baseline characteristics and various echocardiographic parameters among
study subjects. The mean LA size among cases was 4.67 ± 0.65 cm and mean
MVA was 0.93 ± 0.21 cm2.
Severe MS (MVA 1-1.5
cm2) was seen in 44 (55%) subjects while very severe
MS (MVA <1 cm2) was seen in 36 (45%)
subjects. The mean RVSP in cases was 60.01 ± 19.88 mm Hg suggesting
moderate to severe pulmonary hypertension. All three STE derived LA
strain [reservoir strain (LASr), conduit strain
(LAScd) and contractile strain
(LASct)] parameters were significantly reduced among
cases (p <0.001) with mean values of LASr(14.73 ± 8.59%), LAScd (-7.61 ± 4.47%) and
LASct (-7.16 ± 5.15%) when compared to controls where
the mean values were 44.11 ± 10.44%, -32.45 ± 7.63%, -11.85 ± 6.77%
respectively. The interclass correlation coefficient for LA strain
measurement was 0.95 (95% CI: 0.84-0.98) for inter-observer agreement
and 0.97 (95% CI: 0.94-0.99) for intra-observer agreement, indicating
good inter-observer and intra-observer correlations.
The NYHA class III dyspnea was
present in 37 (46.25%) subjects, while thirty-eight (47.5%) subjects
had NYHA class II dyspnea followed by 5 (6.25%) subjects who had NYHA
class I dyspnea. The descriptive statistics associated with patients in
different NYHA classes were analyzed both between the groups and within
group by ANOVA (Table 2). There
was no significant correlation between any echocardiography derived
parameters as well as LA strain parameters between various NYHA classes
except for MVA which was significantly lower in NYHA class III (0.87 ±
0.21 cm2) when compared to NYHA class II (0.97 ± 0.2
cm2) and I (1.18 ± 0.23 cm2) [p=
0.004 between all groups] and RVSP which was significantly higher in
NYHA class III (66.32 ± 19.74 mmHg) when compared to class II (55.03 ±
18.47) [p= 0.01 between NYHA class II and III]. All the three mean
LA strain values (reservoir, conduit, contractile strain) were
numerically lower in NYHA class III when compared to NYHA class I
patients but did not reach statistically significant difference.
We divided cases into groups based on increasing mean diastolic
transmitral gradient (four groups), increasing peak diastolic
transmitral gradient (three groups), increasing left atrial size (four
groups), increasing severity of pulmonary hypertension (four groups) and
decreasing mitral valve area (two groups) to study their correlation
with LA strain (Table 3). The
numerical value of all three STE derived LA strain parameters showed a
trend towards decline with decrease in MVA, increase in LA size and
increase in severity of PH, increase in MG and PG. But none of the above
correlations achieved statistical significance (Table 4).