DISCUSSION
This is the first study in patients with class III obesity to directly compare the feasibility and interpretability of DSE with and without the use of intravenous contrast enhancement, both cumulatively and on a segment-by-segment basis.13-19 The results indicate that in patients with class III obesity, DSE performed using intravenous contrast enhancement is superior to DSE performed without intravenous enhancement, particularly with regard to visualization of the lateral and anterior segments. Moreover, DSE without intravenous contrast was associated with a significantly higher frequency of poor- or non-visualization of ≥ 2 segments (rendering them uninterpretable) than DSE performed with intravenous contrast. Our study consisted of patients with class III obesity without chest pain and without previously documented CAD. Most of our
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patients had at least 1 traditional CV risk factor and many had >1 risk factor. Of the 128 patients studied, 55 were diabetic. Thus, our study population simulated a group of patients with class III obesity who may be referred for stress testing prior to bariatric surgery to screen for myocardial ischemia in the absence of chest pain or documented pre-existent CAD. This comprises the majority of such referrals. Our results further suggest that myocardial ischemia is extremely uncommon in such patients.
Nine prior studies have evaluated patients with various degrees of obesity with transthoracic exercise stress echocardiography (ESE) or DSE to determine the feasibility of these studies in this population (4 studies), to assess prognosis based on the presence or absence of myocardial ischemia and other CV outcomes (8 studies).12-18 or both (3 studies). Lerakis et al studied 611 patients whose BMI was ≥ 40 kg/m2 to determine the feasibility of DSE prior to and the short- and long-term outcomes following bariatric surgery based on the results of the stress test.12 The study population consisted of 86.6% women and 13.4% men (mean age: 42 ± 10 years). The mean BMI was 48.0 ± 6.1 kg/m2 and mean body weight was 136 ± 18 kg. The end-points were all-cause mortality and multiple adverse cardiac events (cardiac death, acute coronary syndrome, urgent coronary revascularization) at 30 days and at 6 months following surgery. Adequate baseline echocardiographic images were achieved in 590 patients (96.6%). Intravenous contrast was used in 72.2% of cases. Those without adequate baseline images were referred for other procedures to assess for myocardial ischemia. DSE was negative in 545 patients (92.4%), was inconclusive in 6.4%, and was positive in 1 patient (1.2%). Laparoscopic surgery was performed in 77% of cases. There were 3 early deaths (all from sepsis). There were no major cardiac events within 30 days of surgery. One patient developed acute coronary
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syndrome between 30 days and 6 months. Shah and colleagues reported the results of the multicenter Study of Ultrasound in Morbid Obesity (SUMO).13 Morbid obesity was defined as a BMI ≥ 35 kg/m2. The study population consisted of 209 subjects who were referred for evaluation of suspected CAD. The mean BMI was 39.3 ± 4.1 kg/m2. ESE was performed in 60% and DSE in 40% of subjects. Intravenous contrast was used in 96% of patients. Mean follow-up was 13 months. Outcomes studied were all-cause mortality, myocardial infarction, and late coronary revascularization. Inducible ischemia was detected in 32 patients (15%). Coronary angiography was performed in 25 patients. Twenty-two had obstructive coronary artery stenotic lesions in distributions that corresponded with the location of myocardial ischemia during ESE or DSE and 77% of whom received coronary revascularization. Predictors of the outcomes were an LV ejection fraction <50% and inducible ischemia. Supariwala and colleagues retrospectively studied 652 consecutive obese patients (BMI ≥ 30 kg/m2) with multiple CV risk factors who underwent stress echocardiography.14 DSE was performed on 423 patients (65%) and 229 (35%) underwent ESE. The study population consisted of 84% women (mean age: 47 ± 10 years). Mean BMI was 47 ± 9 kg/m2 and mean body weight was 280 ± 69 pounds. The study population was 12% Caucasian, 56% Hispanic, and 30% African-American. Mean follow-up was 3.2 ± 2.7 years. The studies were classified as technically difficult in 293 patients (45%) and intravenous contrast was used in 229 subjects (35%). Target heart rate was achieved in 553 patients (85%). The test was considered suboptimal in 64 patients (10%). During the follow-up period, there were 8 deaths. Deaths occurred in 1 patient with obesity (BMI: 30.0-39.9 kg/m2), in 3 patients with extreme obesity (BMI: 40.0-49.9 kg/m2), and in 4 patients with super-obesity (BMI ≥ 50 kg/m2). Hu and co-workers studied 62 patients who were overweight or obese (BMI 26-33
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kg/m2).15 DSE was performed with and without intravenous contrast injection. Visualization of LV segments was scored as 0 (not-visualized), 1 (poorly-visualized), and 2 (well-visualized). A total of 992 segments were assessed. Each patient served as their own control with regard to acquisition of images with and without intravenous contrast enhancement (this process was not clearly-described). Compared to non-utilization of intravenous contrast, use of intravenous contrast was associated with higher sensitivity (82% vs. 70%), specificity (78% vs. 67%), and accuracy (81% vs. 69%). Visualization scores without contrast were 0 in 179 segments (18%), 1 in 328 segments (38%), and 2 in 433 segments (44%). In the group that received intravenous contrast visualization scores were 0 were in 0 segments, 1 in 50 segments (5%) and 2 in 942 segments (95%). Silviera and colleagues performed physical stress echocardiography on 945 obese and 3105 non-obese patients.16 No significant differences were noted in the incidence of myocardial ischemia in obese patients (19.0%) compared to non-obese patients (17.9%). Logistic regression analysis identified age, female gender, diabetes mellitus, and hypertension, but not obesity as predictors of myocardial ischemia. Murphy et al performed a retrospective chart review on 704 patients to determine the prognostic value of a normal stress echocardiogram in overweight and obese subjects.17 The study population consisted of 366 obese patients (BMI ≥ 30 kg/m2), 196 overweight subjects, (BMI 25.0-29.9 kg/m2), and 142 normal weight patients (BMI 18.5-24.9 kg/m2) The follow-up period was 1 year. The end-point was multiple adverse cardiac events (myocardial infarction, cardiac death, cardiac hospitalization, or emergency department visit). No adverse cardiac events were observed during the follow-up period. Khan and co-workers performed DSE on 555 African American patients.18 Intravenous contrast was used when non-contrast images of LV segments were poorly-visualized. There were 409 obese
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and 146 non-obese subjects. Multivariate analysis showed that myocardial scar independently predicted all-cause mortality and multiple adverse cardiac events. There were no significant differences in these outcomes between obese and non-obese groups. In a recently-published case-control study these outcomes between obese and non-obese groups. In a recently-published case-control study of 1018 patients with a BMI > 35 kg/m2 who had suffered prior myocardial infarction and who were followed for a median of 4.6 years, Naislund et al compared long-term CV outcomes in 509 patients undergoing metabolic (bariatric) surgery (predominately Roux-en-Y gastric bypass) and 509 patients with severe obesity (BMI ≥ 40 kg/m2) who did not undergo metabolic surgery.19 Primary outcomes were all-cause deaths and re-admission for myocardial infarction. Secondary outcomes were ischemic or hemorrhagic stroke. Kaplan-Meier analysis showed that metabolic surgery was associated with significantly higher myocardial infarction- and stroke-free survival at 8 years compared to non-surgical controls. Those undergoing metabolic surgery also experienced significantly fewer re-admissions for new-onset heart failure compared to controls. In another recently-published propensity score matched cohort study of 2638 patients with prior CV disease followed for a median of 4.6 years, Doumouras and colleagues reported CV outcomes in 1319 patients with class II and class III obesity undergoing bariatric surgery and 1319 patients who did not undergo bariatric surgery.20 BMI thresholds were > 35 kg/m2 with a co-morbidity or ≥ 40 kg/m2 without a co-morbidity. Patients receiving bariatric surgery had significantly lower incidence values for multiple adverse CV events (all-cause mortality, myocardial infarction, coronary revascularization, cerebrovascular events, and heart failure hospitalizations compared to those of patients who did not undergo bariatric
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surgery. Similar results were noted for a 3-component multiple adverse CV event model (all-cause mortality, myocardial infarction and ischemic stroke.
Our study differed from previous studies evaluating transthoracic stress echocardiography in severely-obese patients in multiple ways. Six of the previous 9 studies were retrospective and relied heavily on chart review or registry information.14,16-19 Our study was prospective and provided a head-to-head comparison of patients with class III obesity receiving intravenous contrast with those who did not receive intravenous contrast. In prior studies, intravenous contrast was used only when baseline non-intravenous contrast images were unsatisfactory except for the study by Hu et al which focused on overweight and mildly obese patients.12-14,16-18 The presence of poor- or non-visualization of ≥2 LV segments, a marker of reduced diagnostic accuracy and interpretability21, occurred with significantly greater frequency in the group that did not receive intravenous contrast group than in the group that received intravenous contrast. In previous studies, ESE or DSE were performed without regard as to whether patients had a history of chest pain or pre-existent CAD.13-18 In our study, we excluded patients with chest pain or pre-existent CAD. We did so to answer the question whether screening lower risk patients with class III obesity for myocardial ischemia was necessary prior to elective low-risk surgery. Our results suggest that they do not require routine screening for ischemia. Regarding feasibility, several prior studies provided the number of patients who received intravenous contrast, but did not cite the precise criteria for these decisions.13,14,17 We not only provided the numbers and percentages of segments well-visualized and interpretable in the intravenous contrast and non-intravenous contrast groups, but also provided a segment-by-segment analysis to determine which LV segments were most likely to be poorly-visualized and
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not interpretable in both groups. Previous studies performing ESE and DSE and did not comment on whether outcomes differed based on the technique that was chosen.13,14,17 Finally, in 7 of the 9 previous studies, the BMI threshold for entry into the study was <40 kg/m2 which indicates that not all patients studied were class III obese patients.13,14,16-18 The BMI in all of our patients was ≥ 40 kg/m2.