3.1 Baseline Characteristics in the ROMICAT cohort
In our cohort of 377 ED patients presenting with chest pain and without atrial fibrillation and significant left-sided valvular heart disease, mean heart rate during CT scan 65 ± 12 beats per minutes with the following CT scanning variables: beta-blockers given in 236 (63%) of patients, sublingual nitroglycerin given in 299 (80%), with ECG tube modulation performed in 167 (46%) of patients. The average age was 53 ± 12 years (range 21 to 89 years), 240 (64%) were men, and LV function was preserved (mean LV EF 67 ± 9%). There were 176 (47%) of patients without any coronary artery plaque by CT. For the cardiovascular event endpoint, 38 (10%) patients had ACS during index hospitalization [30 (79%) unstable angina, 8 (21%) myocardial infarction]. The characteristics of the study group are summarized in . The distribution of LAVmax, LAVmin, LAVImax, and LAVImin are presented in .
Demographics of the study group
Left atrial (LA) volumes and indices in the ROMICAT cohort and “Risk Factor” Group versus “Controls”.
3.2 Comparison of LA measurements in the “Risk Factor” and “Control” groups
In the control group, there were 107 patients included (43 women and 64 men). These patients had no prior history of hypertension, diabetes, hyperlipidemia, history of CAD, and LV dysfunction. They were also determined to have no coronary artery plaque on CT and did not develop ACS during index hospitalization. The remainder of the study group (n=270) were classified as the “risk factor” group and had at least one cardiovascular risk factor, or coronary artery plaque documented on CT. summarizes the means and differences in LA volumes and indices between the risk factor and control groups. Overall, the patients with risk factors had significantly larger LA volumes and indices than the controls (all p<0.05). depicts the LA size differences between a patient in the control and one in the risk factor group.
Figure 1 Three-chamber (A), four-chamber (B) and two-chamber (C) views obtained at end-systole of a patient in the control group, without acute coronary syndrome, and in the lowest quartile of LAVmax. Corresponding views (D–F) in a patient in the “risk (more ...)
3.3 Clinical Predictors of LA volumes
There were no significant differences in LA volumes or indices in those who receive beta-blockers pre-CT scan and those who did not, as well as those who received sublingual nitroglycerin and those who did not (all p=NS). The univariate relationship of cardiovascular risk factors and covariates to LA volumes and indices are shown in . All unadjusted covariates except for family history of premature CAD and smoking were significantly associated to LA volumes. Both increasing age and BMI had weakly positive correlations to LA volumes. Patients who were men, with hypertension, diabetes, hyperlipidemia, history of CAD, and history of LV dysfunction had larger LA volumes than those who were not (all p<0.05). However, when indexed to BSA, women had slightly larger LAVImax and there was no difference between gender with LAVImin.
Univariate relationship of cardiovascular risk factors and covariates to left atrial (LA) volumes and indices.
In multivariable regression analyses (), age, gender, BMI, diabetes mellitus, and history of LV dysfunction were independent predictors of the LA measures, though varied slightly depending on the parameter. Consistently, age and history of LV dysfunction were remained significant for all the LA measures, with an estimated 5 ml increase in volumes and 3 ml/m2 in the indices for every decade increase in age. Patients with history of LV dysfunction had the greatest magnitude of effect and were estimated to have 25–29 ml increase in LA volumes and 11–12 ml/m2 in indices over those who were not. In addition, males trended towards having larger LAVmax (β 5.6 ml, 95% confidence interval [CI]: −0.1, 11.3 ml; p=0.05) than females. However, when indexed to BSA, men had smaller LAVImax by 3.7 ml/m2 than women, which was non-significant with LAVImin (p=0.63). For diabetic patients, in addition to a 9 ml increase in LAVmin and 4.3 ml/m2 increase in LAVImin over their non-diabetic counterpart, they trended towards having larger LAVmax (β 8.4 ml, 95% CI: −0.3, 17.0 ml; p=0.06) and LAVImax (β 4.2 ml/m2, 95% CI: −0.01, 8.3 ml/m2; p=0.05) than non-diabetics.
Multivariable clinical predictors of left atrial (LA) volumes and indices.
3.4 Association and Predictive Value of LA volumes and Indices for ACS
For the ROMICAT cohort, patients with ACS had significantly larger LA volumes (LAVmax: 108.3±31.0 ml vs 96.2±26.6 ml, p<0.01; LAVmin: 68.9±29.2 ml vs 56.6±20.5 ml, p=0.015). Even after indexing for BSA, the LA size differences persisted with larger LA indices in ACS patients than patients without ACS (LAVImax: 53.7 ± 15.5 ml/m2 vs 48.6 ± 12.9 ml/m2, p=0.02; LAVImin: 34.0 ± 14.4 ml/m2 vs 28.6 ± 10.1 ml/m2, p=0.03).
For its association with ACS, we compared patients in the top quartile of LA volumes and indices to those in the lowest quartile (LAVmax: 112.9 – 213.8 ml versus 47.0 – 77.9 ml; LAVmin: 66.2 – 190.5 ml versus 25.7 – 44.7 ml; LAVImax: 57.4 – 101.3 ml/m2 versus 24.0 –39.2 ml/m2; LAVImin 32.9 – 93.9 ml/m2 versus 13.2 – 22.9 ml/m2). For LAVmax, patients in the top quartile had a 3-fold increase risk for ACS (odds ratio [OR] 3.4, 95% CI: 1.2, 9.7; p=0.02) as compared to lowest quartile. Similarly, for LAVmin, there was a near 5-fold increase risk for ACS (OR 4.7, 95% CI: 1.5, 14.7; p=0.01). However, when indexed to BSA, the odds for having ACS when comparing those in the top quartile to lowest quartile of LAVImax (OR 2.6, 95% CI: 0.9, 7.0; p=0.07) and LAVImin (OR 2.5, 95% CI: 0.99, 6.5; p=0.05) were attenuated and no longer statistically significant.
showed the incremental predictive value of LA enlargement for ACS. Using these top versus lowest quartile cutoff values for the LA volumes and indices, there was incremental value for predicting ACS with the addition of the LA volume measures when added to that of positive coronary artery plaque but indeterminate stenosis by CT (LAVmax: C statistic improved from 0.62 to 0.70, p=0.049; LAVmin: C statistic improved from 0.65 to 0.73, p=0.008). While the C statistic increased for the LA indices, these changes were both not statistically significant.
Incremental Predictive Value of LA Volumes and Indices for Predicting Acute Coronary Syndrome.