Ischemic heart disease is a significant public health problem with an estimated prevalence of greater than 1 in 3 adults in the U.S. with some form of cardiovascular disease, including ≥40 million estimated to be ≥ 60 years of age.3 Stable ischemic heart disease (SIHD) is diagnosed by symptoms (e.g., chest pain or ‘ischemic equivalents’ such as shortness of breath (dyspnea), neck/jaw or arm pain, palpitations, dizziness, syncope/near syncope) that are reproducible primarily with exertion and are not progressing in severity. The diagnostic approach for patients with symptoms that suggest SIHD, is to determine whether such symptoms represent the initial clinical recognition of chronic stable angina, a correlate of supply/demand mismatch precipitated by a change in activity or concurrent illness (e.g., anemia or infection).4 Invasive coronary angiography (ICA) is frequently unnecessary in patients with suspected SIHD, as evidenced by low diagnostic yields for significant obstructive CAD. For example, from a sample of over 132,000 ICAs, Patel, et al. found 48.8% of elective ICAs performed in patients with what was thought to be stable angina did not detect obstructive CAD (left main stenosis ≥50% or ≥70% in a major epicardial or branch >2.0 mm in diameter).5 Moreover, for the large majority of patients with SIHD, revascularization offers no survival advantage over medical therapy.1 Noninvasive CCTA is very sensitive in detecting obstructive CAD, but is limited in its positive predictive value.6 CCTA also does not assess the functional significance of visualized lesions, and often leads to further evaluation with either stress testing or invasive angiography, or both.7
Determination of Functionally Significant CAD Using Vessel Anatomy and FFRCT
Although it is recognized that individual coronary anatomy is highly variable, the anatomic construct for CAD is based on the presence or absence of flow-limiting obstructions in the coronary arteries categorized by the number of vessels involved (1-, 2-, and 3-vessel, and/or left main CAD) as well as the amount of myocardium at risk.1
Although imperfect, the commonly used classification of 1-, 2-, and 3-vessel disease and left main disease remains widely used in clinical practice.1 The coronary artery anatomy derived from CCTA can now be augmented with information derived from the physiologic testing of stenosis with FFRCT technology.8,9 The COURAGE investigators, along with outcome data from other trials involving more than 5,000 patients, confirmed that PCI (percutaneous coronary intervention) can be safely deferred with use of optimal medical therapy (OMT) in patients with stable CAD, even in those with multi-vessel involvement and inducible ischemia.10-13 The accepted standards for coronary revascularization in patients with SIHD are outlined in collaborative, multi-society guidelines that define appropriate use criteria for coronary revascularization in patients with SIHD.1,4 These management recommendations are determined by the number of vessels, vessel type, location of stenosis, and intensity of medical therapy.1 When applied to the decision-making for revascularization, FFRCT proves useful in providing information to characterize vessel disease when PCI is a consideration, as opposed to when optimal medical therapy is recommended.
Selective FFRCT Guides Determination for Invasive Coronary Angiography
There is evidence, provided by 2 prospective and 2 retrospective cohort studies, that compares health outcomes observed during 90-day to 1-year follow-up for strategies using CCTA particularly in combination with selective FFRCT with strategies using ICA or other noninvasive imaging tests.
The PLATFORM trial was a prospective, longitudinal, comparative-effectiveness study designed to assess the impact of using FFRCT on stable patients with suspected CAD and referred for ICA.14,15 The primary endpoint (rate of ICA showing non-obstructive disease within 90 days) included a control cohort of 187 consecutive patients referred for ICA (“usual care”) and 193 patients referred instead to CCTA and FFRCT. Exclusion criteria included suspicion of acute coronary syndrome, prior coronary artery bypass graft (CABG), prior PCI, and contraindications for CCTA which included BMI > 35 kg/m2 (supplemental data online). Using information obtained from the FFRCT analysis, clinicians were able to cancel 61% of planned ICAs leading to an 83% reduction in the primary endpoint of ICAs showing no obstructive disease. One-year outcomes reported that FFRCT was safe to use with 0 adverse events for those patients with canceled ICA. It is important to note that this study examined a strategy of using FFRCT to guide management among patients eligible to undergo CCTA testing. 88% of CCTAs performed were of sufficient quality to assess FFRCT consistent with the fact that FFRCT may not be technically feasible in all patients.14
The PROMISE FFRCT study further supports use of FFRCT for guiding referral to ICA.16 This retrospective, observational, cohort study examined whether FFRCT accurately predicts coronary revascularization and adverse events. Using FFRCT to selectively refer patients to ICA improved catheterization lab efficiency by showing a reduction in patients referred to ICA by 28% and an increase in the rate of ICA leading to revascularization by 24%. A positive FFRCT value was significantly better than CCTA at predicting whether a patient had an adverse event or underwent revascularization. In a ‘real world’ patient population and study design resulting in sites not receiving specific FFRCT training and feedback (including standard administration of nitroglycerin and appropriate image reconstruction), the image quality requirements for FFRCT were much more significant. One-third (33%) of the CCTAs sent to the FFRCT core laboratory were inadequate for FFRCT analysis. It is also notable that the BMI of participants of the initial PROMISE CCTA study, the population from which this FFRCT population was derived, reported to the mean BMI to be 30.5 ± 6.1kg/m2.7
The ADVANCE registry (Assessing Diagnostic Value of Non-invasive FFRCT in Coronary Care) included 5,083 patients with symptoms suggestive of angina from 38 centers in Europe, North America, and Japan.17 FFRCT provided information to physicians that resulted in a change in the management plans in two-thirds of patients (66.9%), compared to the management plan after CCTA. The prospective international multi-center study also demonstrated that for patients with CAD by CCTA and a negative FFRCT (>0.80), medical management was safe. There were 0 adverse events at 90 days for the 1592 patients in this group. This contrasts with 19 adverse events (10 death, 4 MI, and 5 hospitalization and urgent revascularization) in patients with positive FFRCT (≤0.80) (MACE hazard ratio 19.75, p<0.001). The investigators concluded that FFRCT can identify patients in need of invasive assessment. Among patients whose post-FFRCT management plan was revascularization and who underwent ICA, 72.6% were re-vascularized. FFRCT effectively differentiated patients who needed further invasive assessment from those who could be managed with medical therapy. A total of 190 subjects did not have their CCTA examinations submitted for FFRCT analysis at the site discretion: 111 because the invasive treatment decision was made due to the severity of the stenosis; 61 owing to minimal CAD; 9 because of multiple coronary stents; 2 because of CCTA exams not acquired in a fashion acceptable for FFRCT analysis.17 BMI characteristics were not reported, however, the U.S. population studied made up less than 23% of the international registry that included patients from Canada, Europe, and Japan and it is not clear from the data if the mean BMI across sites significantly varied (supplemental data).
2-Year FFRCT Data Demonstrate Positive Health Outcomes
Norgaard, et al (NXT Trial) reported 2-year outcomes from a single-center, observational study that included 3,674 consecutive patients with stable chest pain. Participants had a median age of 60 ± 9 years and a BMI of 26 ± 4 kg/m2 and were followed for a median of 24 months (range of 8-41 months) after evaluated with CCTA and selective FFRCT.18 The results demonstrate the ability of physicians to use the FFRCT service to differentiate patients in need of PCI or CABG from those who could be managed with OMT alone. Patients with intermediate stenosis (30-70%) by CCTA who had a negative FFRCT (>0.80) had 2-year outcomes equivalent to patients with no to minimal stenosis (0-30%) by CCTA. The composite endpoint (all-cause death, MI, hospitalization for unstable angina, and unplanned coronary revascularization) was 3.9% for the intermediate stenosis/ FFRCT negative group versus 2.8% for no to minimal stenosis by CCTA group (p=0.58). Additionally, patients with a positive FFRCT (≤0.80) who underwent invasive assessment had fewer MIs than those with a positive FFRCT who were managed medically (1.3% versus 8.0%, p<0.001). This study demonstrated the safety of using FFRCT information to select the best treatment for patients.
Positive Health Outcomes Demonstrated in Medicare Population
Lastly, clinical evidence evaluating 254 Medicare-eligible subjects in a sub-analysis for the NXT study found that FFRCT has a high diagnostic performance compared to invasively measured FFR, identifying patients with hemodynamically significant obstructions with high sensitivity (85%) and specificity (79%) in subjects ≥ 65 years old with stenosis in the intermediate range (30-70%).19 Over 90% of patients in the analysis had the intermediate range stenosis. The data also established that myocardial ischemia is unlikely in patients with FFRCT > 0.80 (negative predictive value (NPV) of 93%) again supporting the role of CCTA with FFRCT as a reliable gatekeeper to ICA and revascularization. Other notable characteristics of the study population include mean BMI of 26 ± 3 kg/m2, normal LVEF of 62% ± 7, and normal renal function. Patient with acute coronary syndrome, previous coronary intervention or bypass surgery, or BMI > 35 kg/m2 were excluded. Additionally, 12% (44) CCTA subjects were excluded due to CCTA image artifacts. Stringent protocols for CCTA acquisition and analysis were also notable with laboratories following quality standards as defined in the Society of Cardiovascular Computed Tomography (SCCT) guidelines.2 This included oral and/or intravenous beta-blockers to achieve to target a heart rate of < 60 beats/min and sublingual nitrates to ensure coronary vasodilation.
Additional literature recommended by the America College of Cardiology (ACC) provided better insight into current anatomic applications and accuracy of the determinations. The SYNTAX family of randomized controlled trials demonstrated that PCI or stenting is a viable option in patients with 3 vessel disease, and in the application of this technology to decision-making regarding CABG or PCI. Use of FFRCT to determine a functional SYNTAX Score (in the SYNTAX III study) reclassified 30% of patients to a lower score.20,21,22 ACC also provided additional literature supporting accuracy of CCTA in obese patients.23,24