Computed tomography (CTA)–derived fractional flow reserve (FFR CT ) guides the need for invasive coronary angiography (ICA). Late outcomes after FFR CT are reported in stable ischemic heart disease but not in acute chest pain in the emergency department (ACP-ED). The objectives are to assess the risk of death, myocardial infarction (MI), revascularization, and ICA after FFR CT . From 2015 to 2018, 389 low-risk patients with ACP-ED (negative biomarkers, no electrocardiographic ischemia) underwent CTA and FFR CT and were entered into a prospective institutional registry; patients were followed up for 41 ± 10 months. CTA stenosis ≥50% was present in 81% of the patients. Positive (FFR CT ≤0.80) and negative FFR CT were observed in 124 (32%) and 265 patients (68%), respectively. ICA was performed in 108 of 124 patients (87%) with positive FFR CT and 89 of 265 patients (34%) with negative FFR CT (p <0.00001). Revascularization was performed in 87 of 124 (70%) patients with positive FFR CT and in 22 of 265 (8%) with negative FFR CT (p <0.00001). Appropriateness of revascularization was established by blinded adjudication of ICA and invasive FFR using practice guidelines; revascularization was appropriate in 81 of 124 (65%) and 6 of 265 (2%) of FFR CT -positive and -negative patients, respectively (p <0.00001). At follow-up, for patients with positive versus negative FFR CT , the rates were 0.8% versus 0% for death (p = 0.32) and 1.6% versus 0.4% for MI (p = 0.24). In conclusion, in low-risk patients with ACP-ED who underwent CTA and FFR CT , the risk of late death (0.2%) and MI (0.7%) are low. Negative FFR CT is associated with excellent long-term prognosis, and positive FFR CT predicts obstructive disease requiring revascularization. FFR CT can safely triage patients with ACP-ED and reduce unnecessary ICA and revascularization.
The use of coronary computed tomography angiography (CTA) in patients in the emergency department (ED) with acute chest pain (ACP) is associated with lower cost and shorter length of stay than other noninvasive modalities. The high sensitivity and negative predictive value of CTA for the identification of coronary artery disease facilitates rapid triage of patients with ACP in the ED; however, patient triage without additional testing may be more problematic in patients with 25% to 70% stenosis. In patients with stable ischemic heart disease (SIHD), CT-derived fractional flow reserve (FFR CT ) is useful in selecting patients for invasive coronary angiography (ICA), and several studies suggest favorable outcomes in patients with negative FFR CT (>0.80). Compared with positive FFR CT , a recent study in patients with ACP reported lower cost and better outcomes at 90 days for negative FFR CT ; however, 31.6% of these patients were referred for ICA, perhaps reflecting the reluctance of cardiologists to rely on CTA/FFR CT in the ED setting. Accordingly, this study aimed to determine the long-term risk of death, myocardial infarction (MI), and revascularization in patients with ACP evaluated with FFR CT and to analyze the indications for ICA and appropriateness of revascularization.
Methods
Between September 2015 and April 2018, 389 low-risk patients with ACP (without increased cardiac biomarkers or ischemic electrocardiographic changes) were evaluated with CTA and FFR CT . Demographic, clinical, CTA, FFR CT , ICA, and clinical outcome data were prospectively entered in the Beaumont Computed Tomography Database. Retrospective review of institutional and regional electronic medical records (EPIC Systems Corporation, Verona, Wisconsin) was performed on all patients. Electronic medical records from 2 neighboring major health care systems were available for review. This study was granted a waiver of consent by the institutional review board of Beaumont Hospital. Those who did not reach a clinical end point were contacted by telephone for follow-up to detect cardiovascular events (death, MI, ICA, percutaneous coronary intervention [PCI], coronary artery bypass grafting). Longitudinal follow-up ended once a clinical event was identified.
CTA was performed using a Siemens SOMATOM Definition FLASH scanner (Siemens Healthcare, Erlangen, Germany) and interpreted by cardiologists board-certified by the Society of Cardiovascular Computed Tomography, as previously described. All patients received β blockers for heart rate control and nitroglycerin to achieve maximal coronary vasodilation. Stenosis severity was graded using Society guidelines. FFR CT was recommended for CTA stenosis grade 2 to 3 (25% to 70% stenosis), high-risk plaque features (positive remodeling, low attenuation plaque, signet ring sign, spotty calcification), , or uncertain stenosis severity because of calcified plaque. FFR CT was measured 10 to 15 mm distal to the lesion of interest (Heartflow Inc., Redwood City, California), as previously reported. The current processing time for FFR CT is 1 to 2 hours for patients in the ED.
The rationale for ICA in patients with negative FFR CT was classified as uncertain stenosis severity (calcification, high-risk plaque features, positive terminal FFR CT ), clinical features suggesting ischemia (abnormal stress test, nonspecific electrocardiographic changes, persistent/recurrent chest pain), and practitioner unwillingness to delay ICA for FFR CT results.
All invasive pressure data (invasive FFR [FFR INV ]) were analyzed by ≥2 interventional cardiologists (BR, RDS, JS) within 4 to 6 months after entry of the last patient into the prospective database. The evaluation of FFR INV included corroboration of pressure sensor location and site of FFR CT measurement and analysis of aortic and distal pressure waveforms (to confirm hyperemia and absence of pressure dampening and drift). Positive pressure values were defined as FFR INV ≤0.8. ,
Cardiovascular events were defined as cardiac death, MI, revascularization, and ICA. MI was defined as ischemic symptoms associated with dynamic ST-T changes and increase of troponin I >0.04 ng/ml. ICA was considered necessary if it led to appropriate/possibly appropriate revascularization and unnecessary if revascularization was not recommended or was considered rarely appropriate. Revascularization was considered appropriate (ICA stenosis ≥90% or ICA stenosis ≥50% plus positive FFR INV ), possibly appropriate (ICA stenosis 50% to 89% and no invasive pressure data or inability to verify FFR INV [unknown sensor location, unavailable pressure tracings]), or rarely appropriate (ICA stenosis <50% and no FFR INV confirmation or ICA stenosis ≥50% with negative FFR INV ), in accordance with practice guidelines and appropriate use criteria. ,
Continuous variables were expressed as mean ± SD. Dichotomous variables were expressed as frequency and percentages. Event-free survival was determined using Kaplan–Meier survival curves; death, MI, revascularization, and ICA were considered independent noncumulative events. Fisher’s exact test was used to compare categorical variables; p <0.05 was considered statistically significant. Statistical analyses were performed using XLSTAT software (Addinsoft, New York, New York).
Results
CTA was performed in 2,302 patients with ACP-ED; 389 patients were further analyzed with FFR CT , including 265 (68%) with negative FFR CT and 124 (32%) with positive FFR CT ( Figure 1 ). Demographic and CTA characteristics are listed in Table 1 ; 314 patients (81%) had grade 3 to 5 stenosis (≥50% stenosis).
| N (%) | |
|---|---|
| Age, years * | 58.9 ± 10.1 |
| Female | 157 (40) |
| Known CAD | 42 (10.8) |
| Non-smoker | 188 (48.3) |
| Diabetes | 64 (16.5) |
| Hypertension | 231 (59.3) |
| Hyperlipidemia | 207 (53.2) |
| CTA Stenosis Grade | |
| ≤ 1 (0-24%) | 19 (4.9) |
| 2 (25-49%) | 56 (14.4) |
| 3 (50-69%) | 233 (59.9) |
| ≥4 (70-100%) | 81 (20.8) |
⁎ Expressed as mean ± standard deviation. CAD = coronary artery disease; CTA = computed tomography angiography.
During the index encounter, ICA was performed in 165 of 389 patients (42.4%), including 100 of 124 (81%) patients with positive and 65 of 265 (25%) with negative FFR CT (p <0.00001) ( Figure 1 ). In 24 patients (19.3%) with positive FFR CT , immediate ICA was not recommended because of small vessels in 10, borderline FFR CT value of 0.75 to 0.8 in 5, and patient or physician preference in 9 patients. Revascularization was performed in 98 of 389 patients (25.2%), including 83 of 124 (67%) positive and 15 of 265 (6%) patients with negative FFR CT (p <0.00001). The ratio of revascularization/ICA was 98 of 165 (59.4%) in patients with positive FFR CT and 15 of 65 (23.1%) in patients with negative FFR CT (p <0.0001). Of 389 patients in the ED, 291 patients (74.8%) were discharged without revascularization during the index encounter ( Figure 1 ).
The attending physician recommended ICA in 89 of 265 patients (33.5%) with negative FFR CT because of uncertain CTA stenosis severity in 88 patients, other clinical features of ischemia in 25 patients, and unwillingness to wait for FFR CT results in 2 patients ( Table 2 ); 38 patients had multiple reasons for ICA.
| A. Why ICA was performed in 89 patients with negative FFR CT | |
| Uncertain Stenosis Severity | 88 (98.9) |
| High-risk plaque features | 13 (14.6) |
| ≥ 50% stenosis by CTA reader | 81 (91) |
| Heavy calcification | 10 (11.2) |
| Positive terminal FFR CT * | 25 (28.1) |
| Clinical Features of Ischemia | 25 (28.1) |
| Troponin I ≥0.04ng/mL | 2 (2.2) |
| Abnormal stress test | 3 (3.4) |
| Abnormal electrocardiogram | 1 (1.1) |
| Persistent/recurrent chest pain | 21 (23.6) |
| ICA Performed Prior to FFR CT Result | 2 (2.2) |
| B. Why index ICA was not performed in 24 patients with positive FFR CT | |
| Small Vessel | 10 (41.7) |
| Borderline FFR CT (0.75-0.8) | 5 (20.8) |
| Physician/Patient preference | 9 (37.5) |
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