Background
Apical ballooning syndrome (ABS) and obstructive coronary artery disease of the left anterior descending coronary artery (LAD) can both result in similar left ventricular apical wall motion abnormalities. The right ventricle may more likely be involved in ABS, and its careful evaluation may help differentiate the two conditions. Therefore, the aim of this study was to determine the roles of echocardiographic measures of right ventricular (RV) function, namely, Doppler tissue imaging–derived RV index of myocardial performance (RIMP), RV basal free wall systolic excursion velocity (RV S′), and tricuspid annular plane systolic excursion, in differentiating ABS from obstructive LAD disease.
Methods
A total of 80 patients with new extensive apical left ventricular wall motion abnormalities on echocardiography who underwent coronary angiography were identified retrospectively. Patients with insufficient echocardiographic data were excluded ( n = 17). Admission clinical and echocardiographic data were compared between patients with obstructive disease of the LAD (LAD group; n = 46) and those with normal coronary arteries (ABS group; n = 17).
Results
The ABS group had significantly greater RIMP (1.03 ± 0.22 vs 0.44 ± 0.18, P < .001). In predicting ABS, RIMP > 0.74 had sensitivity of 94%, specificity of 94%, positive predictive value of 84%, and negative predictive value of 98%, with excellent discriminatory ability (area under the receiver operating characteristic curve, 0.96 ± 0.03). Other measures of RV function (i.e., tricuspid annular plane systolic excursion and RV S′) were similar between the two groups.
Conclusions
Doppler tissue imaging–derived RIMP may help differentiate ABS from obstructive LAD disease with high accuracy. This easily obtainable measurement may offer a noninvasive tool to differentiate these two conditions.
Apical ballooning syndrome (ABS), a form of stress-induced cardiomyopathy, is characterized by electrocardiographic and echocardiographic changes that mimic an acute coronary syndrome involving the left anterior descending coronary artery (LAD) but in the absence of obstructive coronary artery disease. It is estimated that ABS may account for 1% to 2% of patients who have clinical presentations suggestive of acute coronary syndromes. Coronary angiography has been recommended to differentiate ABS from obstructive coronary artery disease. However, such an approach exposes patients with ABS to the various inherent risks of an invasive angiographic procedure. In addition, patients with ABS who present with acute ST-segment elevation are at risk for receiving inappropriate thrombolytic therapy at hospitals that do not offer coronary angiography and primary percutaneous intervention.
Although the involvement of the apical left ventricular segments may be similar to that in obstructive LAD disease, the right ventricle may be more frequently involved in ABS. Thus, careful evaluation of the right ventricle may help differentiate the two conditions. However, this is challenging because of the right ventricle’s complex anatomy and poor two-dimensional (2D) echocardiographic visualization. The commonly recommended echocardiographic measures of right ventricular (RV) function include RV index of myocardial performance (RIMP), RV basal free wall segment excursion velocity (RV S′), and tricuspid annular plane systolic excursion (TAPSE). RIMP overcomes many of the aforementioned challenges because it can be simply determined from tissue Doppler of the tricuspid annulus and is a marker of combined systolic and diastolic ventricular function. RIMP is defined as the ratio of RV isovolumic time divided by RV ejection time (ET). Although the traditional calculation of RIMP involves pulsed-wave Doppler recordings of RV inflow and outflow, it may also be measured from tricuspid annular tissue Doppler recordings. Using tissue Doppler has the advantage of reducing measurement errors from fluctuations in heart rate. Tissue Doppler–derived myocardial performance index has been shown to be a reliable method for the evaluation of RV function, and it correlates well with pulsed-wave Doppler–derived myocardial performance index. Doppler tissue imaging can also be used to obtain RV S′. This is a simple, reproducible technique that can be used to assess RV function and has all the advantages of Doppler tissue imaging techniques. Finally, TAPSE is a technique to measure the distance of systolic excursion of the RV annular segment along its longitudinal plane, from a standard apical four-chamber window using either M-mode or 2D echocardiography. It is also a simple and reproducible technique that is less dependent on optimal image quality despite the limitation of not taking into account the complex three-dimensional structure of the right ventricle. Although these measures of RV function have proved their utility as diagnostic and prognostic tools in a wide variety of cardiac conditions, their role in evaluating RV function in patients with ABS has not been previously studied. Therefore, the objective of this study was to evaluate the roles of RIMP, RV S′, and TAPSE as simple noninvasive tools to help differentiate ABS from obstructive LAD disease.
Methods
Study Design
This was a retrospective cohort study, conducted at a university-affiliated teaching hospital. The study was approved by the local institutional review board.
Between January 1, 2005, and December 31, 2010, all patients who underwent coronary angiography and had new extensive apical left ventricular wall motion abnormalities on echocardiography were identified from the cardiology imaging database. Patients were eligible for inclusion if they had either (1) obstructive LAD disease without concurrent obstructive disease in the other two major epicardial coronary arteries (LAD group) or (2) normal coronary arteries (ABS group). Obstructive disease of an epicardial artery was defined as ≥70% angiographic luminal narrowing of the vessel.
Clinical, Laboratory, and Electrocardiographic Variables
Admission clinical, laboratory, and electrocardiographic data were collected by review of the electronic medical records. Clinical variables included demographic data and the presence or absence of medical conditions including diabetes, hypertension, hyperlipidemia, coronary artery disease, and stroke. Laboratory variables included peak serum levels of cardiac troponin I. Admission 12-lead electrocardiographic variables included the presence of pathologic Q waves, the presence of ST-segment and T-wave abnormalities, and QT interval corrected for heart rate. Abnormal Q waves on 12-lead electrocardiography were defined as Q waves > 30 msec in duration and ≥ 1 mm in depth present in at least two contiguous leads.
Echocardiographic Variables
Left ventricular ejection fraction was estimated using the biplane area-length method. RV function was assessed both by 2D and Doppler tissue imaging (iE33; Philips Medical Systems, Andover, MA). Using 2D echocardiography, RV segmental wall motion was quantified by ascribing standard numeric scores (i.e., 1 = normal, 2 = hypokinetic, 3 = akinetic, and 4 = dyskinetic) in the basal, mid, and apical segments. The RV wall motion score index was obtained by summing the segmental wall motion scores and dividing by the number of visualized segments. Doppler tissue imaging was performed in the apical four-chamber view at a sweep speed of 100 mm/sec, a Doppler gain of 30% to 40% to optimize the image quality, using a low wall filter setting preset by the manufacturer, with the sample volume placed just beneath the lateral aspect of the tricuspid annulus. Doppler tissue imaging has become part of the standard imaging protocol at our laboratory and is performed in all of our echocardiographic studies. However, in some of the echocardiographic studies performed in the earlier part of the study period and in those ordered as limited echocardiographic examinations, Doppler tissue imaging data were not always available. Such patients were excluded from the study. All measurements were performed offline by an experienced staff cardiologist (A.L.R.) blinded to the clinical data of the subjects. RIMP was calculated as (TCO − ET)/ET, where TCO is the time from tricuspid valve closure to tricuspid valve opening, which includes isovolumic contraction time, ET, and isovolumic relaxation time, and was measured as the time interval between the end of atrial systolic contraction (a′) of the preceding cardiac cycle and the beginning of early diastolic tricuspid valve annular velocity (e′) wave of the subsequent cardiac cycle ( Figure 1 ). The tissue Doppler image obtained above was also used for measuring RV S′ velocity, read as the highest systolic velocity, without overgaining the Doppler envelope. TAPSE was obtained in the apical four-chamber view by measuring the amount of longitudinal motion of the annulus at peak systole using 2D echocardiography. Pulmonary artery systolic pressure was estimated from the peak tricuspid regurgitation jet velocity, using the simplified Bernoulli equation and combining this value with an estimate of right atrial pressure (4 × [peak tricuspid regurgitant velocity] 2 + right atrial pressure). Right atrial pressure was estimated from inferior vena cava diameter and respiratory changes as previously described.
Statistical Analysis
Categorical data were compared using χ 2 tests or Fisher’s exact test (when the expected value in any of the cells of a contingency table was <5). Continuous data are reported as mean ± SD and were compared using Student’s t tests or Wilcoxon’s signed-rank test as appropriate. The predictors were initially identified by univariate analysis and if found significant were subsequently included in a multivariate model. A receiver operating characteristic (ROC) curve was constructed for the RIMP values, and the area under the ROC curve was calculated as a measure of the discriminative ability of the model. Intraobserver and interobserver agreement was calculated for RIMP, RV S′, and TAPSE using the intraclass correlation coefficient (ICC) and was considered to be excellent if the ICC was >0.8 and substantial if the ICC was between 0.60 and 0.79. In a randomly chosen sample of 10 patients from our study, for the measurement of RIMP, there was substantial interobserver agreement (ICC = 0.66) and excellent intraobserver agreement (ICC = 0.88). For the measurement of RV S′, the interobserver agreement (ICC = 0.99) and intraobserver agreement (ICC = 0.99) were both excellent. Similarly, for TAPSE, there was excellent interobserver (ICC = 0.98) and intraobserver (ICC = 0.84) agreement. P values < .05 were considered to indicate statistical significance. All analyses were performed using PASW Statistics version 18 (SPSS, Inc, Chicago, IL).
Results
A total of 80 patients met the inclusion criteria, of whom 17 patients lacking Doppler tissue imaging data were excluded. Of the remaining 63 patients who were included in the study, 46 were in the LAD group and 17 in the ABS group. Notably, tissue Doppler and TAPSE measurements were feasible in all 63 patients included in the study. The mean age of the study population was 57 ± 11 years, 26 (41%) were women, 45 (73%) were Caucasians, and the mean left ventricular ejection fraction at admission was 39 ± 13%. Age and race were comparable between the two groups. Importantly, there was no significant difference between the two groups with respect to the time interval between performing cardiac catheterization and echocardiography (6.4 ± 12.6 days in the ABS group vs 4.3 ± 11.9 days in the LAD group, P = .71). Patients with ABS were more likely to be women, while patients in the LAD group were more likely to have histories of hypertension and abnormal Q waves on 12-lead electrocardiography ( Table 1 ). In addition, the two groups were similar with respect to the presence of ST-segment changes and T-wave abnormalities on 12-lead electrocardiography.
| Variable | ABS group ( n = 17) | LAD group ( n = 46) | P |
|---|---|---|---|
| Age (y) | 57 ± 12 | 57 ± 11 | .84 |
| Women | 13 (76%) | 13 (28%) | <.001 |
| Caucasian | 13 (76%) | 32 (70%) | .31 |
| History of hypertension | 3 (18%) | 31 (67%) | <.001 |
| History of diabetes | 3 (18%) | 14 (30%) | .24 |
| Stroke | 0 (0%) | 11 (24%) | <.05 |
| Peak cTnI (ng/mL) | 7.6 ± 8.2 | 83.1 ± 131.3 | <.05 |
| Length of stay (d) | 6.6 ± 8.2 | 6.7 ± 6.1 | .54 |
| 12-lead ECG findings | |||
| Abnormal Q waves | 1 (6%) | 21 (46%) | <.05 |
| QTc interval (msec) | 459 ± 31 | 453 ± 34 | .28 |
Echocardiographic Variables
Left ventricular ejection fraction was comparable between the two groups, whereas RV impairment was more common in patients in the ABS group ( Table 2 ). RIMP was significantly greater in the ABS group than in the LAD group (1.03 ± 0.22 vs 0.44 ± 0.18, P < .001; Figure 2 ). Using the ROC curve, the optimal cutoff point for abnormal RIMP was determined as >0.74, who had sensitivity of 94%, specificity of 94%, positive predictive value of 84%, and negative predictive value of 98%, with excellent discriminatory ability (area under the ROC curve, 0.96 ± 0.03; Figure 3 ). Using the above cutoff point, Doppler tissue imaging–derived RIMP identified abnormal RV function in as many as 16 patients (94%) in the ABS group, compared with only four (9%) in the LAD group ( P < .001). In contrast, using only visual assessment of RV function by 2D echocardiography, abnormal RV function was demonstrated in a smaller proportion of patients with ABS, although it was still higher than in the LAD group (10 [67%] vs 11 [30%], P < .05 for all comparisons). Furthermore, TAPSE and RV S′ were comparable between the two groups and therefore were not helpful in differentiating ABS from LAD disease.
