Comparison of coronary computed tomography angiography, fractional flow reserve, and perfusion imaging for ischemia diagnosis

Selected in the Journal of the American College of Cardiology by J. Bil , C. Cook

A study to evaluate the diagnostic performance of FFRCT and compare it with coronary CTA, single-photon emission computed tomography, and positron emission tomography for ischemia diagnosis.

Reviewers

Jacek Bil

Interventional cardiologist / Cardiologist

Centre of Postgraduate Medical Education - Warsaw, Poland

Christopher Cook

@CCook_MD

Interventional cardiologist / Cardiologist

The Essex Cardiothoracic Centre - Basildon, United Kingdom

Our Comment

This joint review is part of the PCRonline GLOBAL Journal Club Initiative by selected members of the EAPCI/PCR Journal Club and PCR NextGen, and is based on the underlying idea of “Bringing peers together, exchanging ideas, towards a common standard of care”.

Why this study – the rationale/objective?

After the publication of FAME, verification of the hemodynamic significance of lesions located in epicardial coronary arteries started to play a key role in revascularization decision-making in patients with stable coronary artery disease (CAD). Before the era of FFR/iFR, a wide range of noninvasive imaging modalities were applied such as echocardiography or SPECT. Presently, we are now witnessing the rising popularity of another modality - FFR computed from coronary computed tomography angiography (CTA) datasets (FFR-CT).

There is much debate as to the role of FFR-CT in routine clinical practice. In particular, comparative studies investigating the diagnostic performance of FFR-CT against other functional imaging modalities are still lacking.

How was it executed – the methodology?

This was the post hoc substudy from the PACIFIC trial (NCT01521468), in which patients with an intermediate pre-test likelihood of stable CAD and normal left ventricular ejection fraction (LVEF) were included:

• 208 patients were enrolled,
• Patients underwent the following noninvasive tests: 256-slice coronary CTA (FFR-CT values derived retrospectively), 99mTc-tetrofosmin SPECT and [15O]H2O PET,
• Invasive coronary angiography and FFR were performed within 2 weeks of noninvasive testing regardless of the imaging results,
• Analyses were performed by a core laboratory (using FFR cut-off ≤ 0.80 as the reference standard).

What is the main result?

• 505 of 612 (83%) vessels were deemed feasible to be evaluated with FFR-CT
• FFR-CT showed a diagnostic accuracy, sensitivity, and specificity of 87%, 90%, and 86% on a per-vessel basis and 78%, 96%, and 63% on a per-patient basis, respectively. 
• In the ROC analysis the area under the curve (AUC) for identification of ischemia-causing lesions was significantly greater for FFR-CT (0.94 and 0.92) when comparing with CTA (0.83 and 0.81; p < 0.01 for both) and SPECT (0.70 and 0.75; p < 0.01 for both), on a per-vessel and -patient level, respectively. 
• FFR-CT was also superior to PET on a per-vessel basis (AUC 0.87; p < 0.01), but not on a per-patient basis (AUC 0.91; p = 0.56).

Critical reading and the relevance for clinical practice

This study adds some new data to the already known information coming from three previously published studies, i.e. DeFACTO (Determination of Fractional Flow Reserve by Anatomic Computed Tomographic Angiography), PACIFIC (Prospective Comparison of Cardiac PET/ CT, SPECT/CT Perfusion Imaging and CT Coronary Angiography With Invasive Coronary Angiography) and NXT (Analysis of Coronary Blood Flow Using CT Angiography: Next Steps). However, a significant proportion of vessels were assessed as non-appropriate to be analyzed in FFR-CT. This rate could be as high as 20%. 

Because of this relatively high rejection rate for FFR-CT, in this head-to-head trial, FFR-CT characterized the highest diagnostic performance for vessel-specific ischemia, but on the intention-to-diagnose basis, PET outperformed FFR-CT. 

Additionally, when interpreting the results of this study one should also remember that these findings only apply to patients with normal LVEF and without documented history of CAD. 

In summary, we do not yet have a definitive answer to the question of which imaging modality is currently the most accurate for the noninvasive assessment of coronary lesions. Furthermore, decisions on the type of non-invasive ischemia testing performed by cardiologists are dependent on many factors including local availability, expertise and cost. In order to truly optimize and standardize non-invasive ischemia testing, clinical outcome data from prospective, randomized clinical trials is needed.