TABLE 2.

Clinical assessment of microvascular obstruction (Giugliano et al., 2004; Bulluck et al., 2017).

Non-invasive parameters	Thrombolysis in myocardial infarction (TIMI) flow	TIMI is a widely used visual assessment of flow appearance that provides immediate evaluation of microvascular reperfusion. It ranges from TIMI 0–3 with TIMI 3 being complete antegrade flow following intervention
		Angiographic definition of MVO is TIMI grade <2 (Bulluck et al., 2017)
	ECG ST segment resolution	ST-segment resolution of <70% at 60–90 min post reperfusion in the presence of a patent epicardial coronary artery is suggestive of MVO (Schröder, 2004)
	Myocardial blush	Grade 0: Absence of myocardial blush, contrast density or persistent “staining” suggestive of leakage of the contrast medium into the extracellular space
		Grade 1: Minimal myocardial blush or contrast density
		Grade 2: Moderate myocardial blush or contrast density but less than that obtained from the contralateral or ipsilateral non-infarct related coronary artery
		Grade 3: Normal myocardial blush or contrast density, comparable with that obtained during angiography of a contralateral or ipsilateral non-infarct related artery. (Van 't Hof et al., 1998) MBG of 0–1 is associated with increased all-cause mortality in patients with STEMI and a score or 2–3 is strongly associated with reduced all-cause mortality (Rehman et al., 2021; Cruz et al., 2022).
	Cardiac Magnetic Resonance	MVO is detected with early gadolinium enhancement by presenting as low signals or hypo-enhacement (dark areas) on CMR. These dark zones of no-reflow tend to fill in (appear bright) on delayed sequences due to penetration of gadolinium into the damaged capillaries.These dark regions correlate with no reflow regions suggesting MVO (Marcus et al., 1990; Wu et al., 1998).
Invasive parameters	Flow Based Parameters	CFVR is the ratio of hyperaemic coronary flow: resting flow measured using a Doppler velocity wire. It reflects epicardial and microvascular vasodilator capacity. CFR ratio of ≥2 is considered normal (Van De Hoef et al., 2013; Bulluck et al., 2016)
		Deceleration time of diastolic coronary flow velocity: Rapid deceleration time <600 m is associated with MVO and poor long term outcomes after reperfusion (Hirsch et al., 2008).
		Systolic flow reversal: The presence of early systolic flow reversal in intracoronary Doppler recordings is associated with MVO (Furber et al., 2004).
	Resistance Based Parameters	IMR is defined as distal coronary pressure times the mean transit time of a 3 mL bolus of saline at room temperature during maximal coronary hyperaemia. It is a thermodilution-derived index, measured using a guidewire that combines a pressure and temperature sensor.
		IMR <25 U is indicative of normal microvascular perfusion (Furber et al., 2004).
		HMR is the ratio between hyperaemic mean distal pressure and hyperaemic average Doppler flow peak velocity. HMR ≥2.5 suggests MVO (Berry et al., 2015).
		Pzf is defined as the distal coronary pressure when theoretically there is no flow in the coronary artery (Patel et al., 2015).