Table 2.

Diagnostic methods of the no-reflow phenomenon.

Diagnostic Methods	Characteristic, Observations	Ref.
Classical
ECG	Definition of the NR phenomenon: Persistence of the ST segment after perfusion of the culprit coronary artery disease by thrombolysis or coronary angiography. ST segment resolution recorded at 1 h after PCI is expected to exceed 70%. An ST segment resolution less than 70% at 1 h is a marker of NR. A successful myocardial reperfusion involves rapid ST segment resolution, parameter very specific (91%), sensitivity moderate (77%).	Caiazzo et al., 2020, Tatu-Chițoiu et al., 2014 [113,114]
Coronary angiography	Enhances semiquantitative assessment of the epicardial coronary blood flow. A suboptimal TIMI flow grade and blush grade, as well as a prolonged “TIMI frame count” indicate the detection of NR. Even if the sensitivity of TIMI flow evaluation is modest, corroboration between MBG grade and ST segment evaluation has a prognostic impact independent of the revascularization method, an aspect that requires accurate assessment of the two elements. MBG 2 to 3 is associated with a rapid ST segment resolution >70%, correlated with a favorable prognosis. CTFC is the summed frame count from the interventional opening of the coronary artery responsible for the MI to the crossing of the contrast substance distally post-revascularization. CTFC is considered the “gold standard” for NR evaluation. Routine assessment of anterior descending artery CTFC compared to the other epicardial coronary arteries is required due to its importance and size. An extended frame count above 20 is a criterion for the detection of NR.	Gupta et al., 2016 Sorraja et al., 2005 Thygesen et al., 2018 Khan et al., 2020 Seyfeli et al., 2007 Bauer et al., 2020 Kaya et al., 2007 Giugliano et al., 2004 [27,74,115,116,117,118,119,120]
Modern
MCE	Absence or poor presence of the contrast substance administered during myocardial echocardiography indicates NR. We should assess the success of post-STEMI myocardial reperfusion compared to coronary angiography.	Kaul et al., 2006 [121]
Intracardiac Echocardiography	The reversal of systolic flow, anterograde reduction of systolic flow, and diastolic flow with a rapidly decelerating slope defines the NR phenomenon. Post PPCI patients with NR due to distal microembolization will present slow intracoronary flow velocity throughout the cardiac cycle.	Ramjane et al., 2008 [4]
CMRI	Provides highly accurate assessment of myocardial tissue. Detects the presence and extension of the infarcted area, tissue oedema present in the infarct area, and MVO as the expression of the NR phenomenon. First contrast agent injection illustrates myocardial perfusion, while delayed contrast myocardial MRI reveals myocardial necrosis. High spatial resolution allows assessment of the transmural extent of the NR, as well as the infarcted area.	Wu et al., 2012 [122]
SPECT	Good accuracy in assessing the degree of myocardial flow, as well as the presence of vascular micro-obstruction. Reproduces the degree of NR. NR appears as vascular micro-obstruction characterized by hypo-amplification due to reduced blood flow.	Shimizu et al., 2006 [96]
PET	Highly accurate for NR detection. Non-invasive diagnostic technique without major adverse effects. Shows in detail the hypoxic myocardial territory but it is less used in current practice due to the high cost.	Jeremy et al., 1990 [123]

ECG, electrocardiogram; TIMI, thrombolysis in myocardial infarction; MBG, myocardial blush grade; CTFC, corrected TIMI frame count; MCE, myocardial contrast echocardiography; STEMI, segment elevation myocardial infarction; PCI, percutaneous coronary intervention; CMRI, cardiac magnetic resonance imaging; SPECT, single photon emission computed tomography; PET, positron emission tomography, NR, no-reflow; MVO, microvascular obstruction.