Diagnostic accuracy of invasive and non-invasive testing
The study by Bråtena et al1 showed that the accuracy, sensitivity and specificity of dobutamine stress echocardiography (DSE) were 61%, 43% and 75% against fractional flow reserve (FFR) and 64%, 46% and 74% against instantaneous wave-free ratio (iFR) in 102 patients with positive coronary CT angiography (CCTA), with low to medium pretest probability (23±13). The diagnostic accuracy of DSE did not differ significantly between FFR and iFR as the reference (p=0.549).
One of the strengths of this study is the challenging question that the authors clearly outlined, giving some historical perspective: what are the gold standards for diagnosing coronary artery stenosis and their prognostic significance in ischaemic heart disease?
Stress echocardiography has long been a strong determinant of the significance of coronary artery stenosis and risk stratification for future events. However, it has some shortcomings, including its suboptimal acoustic window, the importance of matching cross-sectional planes prestressor and poststressor, and its operator dependence; it is also time-consuming in the era of fast food, like old grandma's chicken soup. All these led to the development of FFR by Dr Nico Pijls and others,2 which was tested against stress echocardiography to determine the cut-off values. The intention was to have a one-stop shop in the cath lab rather than relying on stress echocardiography. The industry jumped in with their interest, resulting in more support for randomised controlled trials (RCTs) for FFR (iFR, etc)3 than for stress echocardiography. Eleven trials, including some meta-analyses, demonstrated that FFR is more effective than angiography in guiding percutaneous coronary intervention (PCI). However, there are five trials, all RCTs, with negative results.4 It is worth noting that no individual RCT compares stress echocardiography with FFR or iFR in terms of decision-making. There is one retrospective non-randomised trial that has shown the superiority of stress echocardiography (using DSE segmental wall motion abnormality) over FFR in the risk stratification, regardless of whether PCI was performed or not.5
Nevertheless, in the latest ‘2024 European Society of Cardiology Guidelines for the management of chronic coronary syndromes’,3 FFR is determined to be of class 1, level of evidence A, while stress echo is of class 1, level of evidence B.6 Of particular note is the fact that reference 1173 in the guidelines concludes that stress echocardiography has no value post-PCI.7 This conclusion was false as only 0.59% (10 out of 1706) of patients underwent stress echocardiography. It is even more misleading as these numbers are not in the manuscript but was only discovered by someone curious enough to search for it in the supplement.
So can someone believe that stress echocardiography with left ventricular volumetry (power index), lung ultrasound (B-lines), heart rate reserve and the possible addition of coronary velocity flow reserve of the left anterior descending artery (the so-called ABCDE protocol) may be a better diagnostic and risk stratification tool for major adverse cardiovascular events and all-cause mortality than just one number, that is, FFR or iFR? There is a lot of ongoing research on advanced stress echocardiography8 9 and adopting and implementing new findings into practice is not easy. Although it may sound too pessimistic, 1918 Nobel Prize winner Max Planck’s quote is still relevant: ‘The new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it’.
Of particular note is that not all stressors are equal in terms of their existence in real life (exercise, mental and cold stress, hyperventilation, shovelling snow, etc), including the so-called pharmacological stressors, which are more suitable in imaging (but patients do not inject dobutamine, atropine, adenosine, etc, in everyday life). They act on different demand–supply scales and may be allies. A metaphor using the fisherman approach is depicted in figure 1.10 11