3.1 – Study selection
The search retrieved 355 individual studies that were filtered by
language, title and abstract leaving 21 original studies. Nine studies
were then excluded at full text, mostly for not reporting on patients
who had undergone coronary angiography although one study was excluded
for unclear results(2) and another excluded for
reporting on the same patients as another study(11).
This left 12 original studies published between 1974 and 2017 included
in this review. Figure 2 shows the selection process.