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CT-Derived fractional flow reserve reduces unnecessary caths in stable CAD

The use of a diagnostic strategy with fractional flow reserve (FFR) derived from computed tomography (CT) significantly reduces the number of patients requiring invasive coronary angiography, with investigators reporting that a large percentage of scheduled diagnostic catheterizations were safely canceled after functional and anatomic information was obtained from FFRCT.

In the study, known as the Prospective Longitudinal Trial of FFRCT: Outcome and Resource Impacts (PLATFORM), the use of CT followed by an FFR calculation in stable coronary artery disease patients scheduled for a planned invasive catheterization was associated with a reduction in the percentage of patients in whom no obstructive disease was identified during the coronary angiography.

For those who underwent planned invasive diagnostic angiography without FFRCT, 73% of patients in the “usual-care” arm had no obstructive disease compared with just 12% of patients who underwent diagnostic angiography based on information from the FFRCT test.

“The use of FFRCT resulted in the cancellation of 61% of invasive angiographies and doubled the availability of functional data at the time of revascularization,” lead investigator Dr Pamela Douglas (Duke Clinical Research Institute, Durham, NC) said during the European Society of Cardiology (ESC) 2015 Congress.

Step Up Onto the PLATFORM

The FFRCT system (HeartFlow, Redwood City, CA), which quantifies FFR using data obtained from a standard CT scan, is intended to provide both anatomic data—from the CT scan—and functional data about any identified ischemic lesion in patients with suspected coronary artery disease. With this system, data obtained from the CT scan is forwarded to HeartFlow, where the FFR is estimated using computational flow dynamics and proprietary software. The turnaround for the FFR data is 1 to 2 days.

The PLATFORM study included two arms: 204 patients undergoing planned noninvasive testing and 380 patients undergoing planned invasive testing with diagnostic angiography. In both study groups, patients were assigned to usual care or an FFRCT-guided strategy.

For 380 patients assigned to the planned invasive coronary angiography arm—all patients had stable coronary artery disease symptoms and an intermediate pretest probability of disease—187 were treated with usual-care invasive angiography while 193 underwent FFRCT testing prior to the scheduled angiogram. The study’s primary end point was the percentage of patients without obstructive coronary artery disease at 90 days as assessed by coronary angiography or invasive FFR.

In the planned invasive testing arm, 193 patients underwent CT angiography and 117 of these patients had FFRCT data submitted and analyzed. As noted, 61% of angiograms were canceled after physicians obtained data from the FFRCT, sending just 76 patients on for an invasive catheterization. Of these patients, just 12% did not have any obstructive coronary disease on diagnostic angiography. In contrast, 73% of patients assigned directly to diagnostic angiography did not have any evidence of coronary artery disease on the angiogram.

Although FFRCT filtered out the number of patients sent for a diagnostic angiogram, the rates of revascularization were similar between patients assigned to standard testing and those assigned to the FFRCT-guided strategy. Importantly, there were no clinical events in the 90-day follow-up period among patients who had the angiogram canceled based on the FFRCT.

In the 204 patients undergoing planned noninvasive testing, the use of the FFRCT-guided strategy did not reduce the number of patients without obstructive disease when compared with usual care at 3 months when patients underwent their planned diagnostic angiogram.

According to Dr. Douglas, if there is nothing on the CT—if the CT looks clean, as it does in 30% to 40% of patients—those patients are done and you don’t need to do anything else. In the others, you take the images you already have and then forward them for the [FFRCT] analysis. The next day you have the information and know what bucket you’re in. You know obstructive or nonobstructive from the CT, but what you really want to know is whether or not you need to intervene.

During the late-breaking clinical-trials session, Dr Keith Fox (University of Edinburgh, Scotland) questioned the high number of patients in the assigned diagnostic angiogram arm who didn’t have obstructive disease, also homing in on the pretest probability of disease used in the trial. Douglas admitted 73% is a large percentage of patients not having obstructive disease but noted this number was lower (57%) when the angiograms were read on-site by physicians rather than the core lab.

For the big picture, Douglas said invasive cardiologists are concerned about the high rate of not finding obstructive coronary disease when a patient is taken for a diagnostic angiogram. “There have been numerous population studies—we published two from the [National Cardiovascular Data Registry] NCDR with hundreds of thousands of patients—showing that more than half of patients undergoing invasive procedures do not have obstructive disease,” said Douglas. “That becomes a really important quality-of-care issue.”

She added that while she is not an interventional cardiologist, “most interventionalists want to do interventions. If they’re spending their day doing diagnostic caths on people who don’t have obstructive disease, there are not a lot of interventions happening that day.”

Reference:

  1. Douglas P et al. Outcomes of an FFRCT diagnostic strategy versus usual care in suspected coronary artery disease: results from the PLATFORM (Prospective Longitudinal Trial of FFRCT: Outcome and Resource Impacts) study. European Society of Cardiology 2015 Congress; September 1, 2015; London, UK. Abstract 5995.

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