No-Reflow and Slow Flow During PCI: A Complete Management Guide-

No-reflow is the moment every interventionalist dreads: the lesion is open, the stent is beautifully expanded, and the distal bed simply will not fill.

This guide is a working, cath-lab-ready reference on recognising, preventing and treating no-reflow and slow flow during PCI. It is aligned with the 2025 ACC/AHA/ACEP/NAEMSP/SCAI acute coronary syndrome guideline, the 2023 ESC ACS guideline and the 2024 SCAI expert consensus on primary PCI.

It is written for interventional cardiologists, interventional fellows and cardiology trainees preparing for board and exit examinations. Doses, algorithms and trial data are presented in the order you actually need them at the table.

What Is No-Reflow? Definitions and Grading

No-reflow is the failure to achieve adequate myocardial tissue perfusion despite a patent, mechanically successful epicardial result. Slow flow is the same disease process at a milder point on the spectrum. Both reflect microvascular obstruction (MVO), not a problem in the vessel you can see.

The distinction matters because the treatments differ in urgency, not in kind. Slow flow that is ignored frequently becomes no-reflow within minutes.

Angiographic grading you should document in every report

TIMI grade alone is not enough. A vessel can be TIMI 3 and still have a devastated microcirculation — which is exactly why MBG and ST-segment resolution belong in your documentation.

Physiology-based assessment

The index of microcirculatory resistance (IMR) is the invasive reference standard. In non-ACS patients an IMR ≥25 defines coronary microvascular dysfunction. In STEMI roughly half of patients have IMR >25, but only IMR >40 correlates with cardiac-MRI-confirmed MVO and with poor clinical outcomes.

Continuous-thermodilution minimal microvascular resistance (MMR), measured with saline infusion at 15–30 mL/min through a dedicated microcatheter, is operator-independent, needs no hyperaemic agent, and predicts IMR >40 well after primary PCI. Angiography-derived indices are convenient but correlate poorly with true microvascular resistance.

How Common Is No-Reflow, and Why It Matters

Depending on the definition used, some degree of impaired microvascular reperfusion is described in up to 40–50% of PCI procedures, and it is far more frequent in STEMI. The number that should change your practice comes from cardiac MRI.

Among STEMI patients who finish the case with angiographically normal TIMI 3 flow, normal myocardial perfusion on cardiac MRI is present in only 24% on day 1, 31% on day 2, 35% on day 4 and 43% on day 8. Angiographic success routinely overstates tissue-level success.

In a pooled cardiac-MRI analysis of 1,688 STEMI patients, MVO was present in 57% and was independently associated with death or heart-failure rehospitalisation at one year. MVO is not a cosmetic angiographic nuisance — it is an infarct-size and mortality signal.

Pathophysiology: Four Mechanisms Behind No-Reflow

Understanding which mechanism dominates in front of you determines which drug you reach for. Four processes overlap.

1. Distal embolisation. Device manipulation liberates platelet–fibrin aggregates, cholesterol crystals and cellular debris into arterioles and capillaries. Glycocalyx shedding exposes adhesion molecules, amplifying leukocyte rolling and platelet tethering. This mechanism dominates in high thrombus burden, degenerated saphenous vein grafts and atherectomy of long calcified lesions.

2. Microvascular vasoconstriction. Endothelial nitric oxide synthase uncouples, producing superoxide rather than nitric oxide, while endothelin-1 rises. Pericytes — contractile cells wrapping the capillaries — constrict via calcium and Rho-kinase signalling. When mean coronary perfusion pressure falls below roughly 45 mmHg, ischaemic capillary derecruitment adds a further mechanical component.

3. Reperfusion injury. Succinate accumulated during ischaemia is rapidly oxidised at reperfusion, producing a burst of reactive oxygen species alongside myocyte calcium overload. Mitochondrial permeability transition pore opening and sarcomere hypercontracture follow, compressing capillaries from the outside.

4. Inflammation and microthrombosis. Platelet–leukocyte aggregates and neutrophil extracellular traps (NETs) scaffold microthrombi, bind von Willebrand factor and tissue factor, and occlude capillaries. This is the step that converts reversible slow flow into durable, treatment-resistant no-reflow.

Who Is at Risk: Predictors of No-Reflow Before You Start

Anticipating no-reflow is worth more than treating it. Screen every case across three domains.

The SCAI 2024 consensus adds an important practical rule: grade thrombus burden only after the wire has crossed the lesion. Thrombus grade 4–5 is “large”; grades 0–3 are small or none. Pre-wire grading systematically misleads.

Preventing No-Reflow: What to Do Before the Stent

Pharmacological groundwork. Adequate pre-procedural antiplatelet loading, therapeutic anticoagulation and high-dose statin pre-treatment are the cheapest prevention available. A meta-analysis of 11 studies (n = 4,294) found high-dose statin loading before PCI significantly reduced post-procedural no-reflow.

Prophylactic distal vasodilatation. SCAI 2024 explicitly endorses maximising distal capacitance with intracoronary vasodilators — adenosine, nitroprusside or a calcium channel blocker — before stenting, and repeating them before and after each coronary manipulation (thrombectomy, angioplasty, stenting).

Lesion preparation strategy. A stepwise approach for a thrombotic occlusion works well in practice:

1. Wire the vessel, then reassess TIMI flow and thrombus grade.
2. If TIMI 2–3 is restored, consider direct stenting to minimise embolisation.
3. If TIMI 0–1 persists, undersized balloon predilatation at a 0.5–0.8:1 balloon-to-artery ratio, with vasodilator cover.
4. If flow still does not recover, add bailout aspiration thrombectomy for large residual thrombus.
5. If flow remains TIMI 0–1 with heavy thrombus, defer stenting, continue potent antithrombotic therapy, and return in 24–48 hours.

Stenting into an unperfused bed converts a recoverable problem into a permanent one. Deferring is not a failure — DEFER-STEMI reduced slow/no-reflow from 29% to 6%, although the larger DANAMI-3-DEFER trial found no clinical-endpoint benefit, so reserve deferral for the genuinely high-risk thrombotic case.

The First 60 Seconds: Confirm No-Reflow and Exclude Its Mimics

Before a single microgram of vasodilator is given, exclude the conditions that look identical on angiography but need the opposite treatment.

• Coronary dissection or wire in a false lumen. Advance a microcatheter distally and inject 1–2 mL of contrast selectively; use IVUS or OCT to confirm true-lumen wire position and stent expansion.
• Epicardial spasm. Give intracoronary nitroglycerin first and re-image.
• Stent underexpansion or edge dissection. Intravascular imaging answers this in seconds; a mechanical problem needs a mechanical solution.
• Air embolism. Distinctive, immediate and treated with forceful saline flushing and 100% oxygen, not vasodilators.
• Residual proximal thrombus or side-branch occlusion. Repeat angiography in a second projection.

Only after these are excluded should you commit to the no-reflow pathway. Misdiagnosed dissection treated with nitroprusside is a preventable catastrophe.

Step-by-Step Treatment Algorithm for No-Reflow

Step 1 — Stabilise the haemodynamics first

Microvascular flow depends on perfusion pressure. Restoring mean arterial pressure and lowering LV end-diastolic pressure is a therapy for no-reflow, not merely supportive care, and SCAI 2024 lists it alongside vasodilators as a core consensus recommendation.

• Hypotension: volume plus norepinephrine to restore mean arterial pressure.
• Bradycardia or AV block: atropine, and a temporary pacing wire before giving adenosine or verapamil.
• RV infarction: volume plus dobutamine.
• Cardiogenic shock: inotropes, vasopressors and early consideration of mechanical circulatory support.

Step 2 — Deliver the drug to the distal bed, not the guide

This is the single highest-yield technical point in the whole algorithm. In a 108-patient four-group comparison of delivery route, distal delivery through a microcatheter, over-the-wire balloon or aspiration catheter achieved TIMI 3 plus MBG 2–3 in 63% of patients versus 27.8% with guide-catheter injection (p < 0.01) — while the choice of agent made no significant difference. Route beat drug.

Step 3 — Escalate pharmacologically

1. First line: intracoronary vasodilator to the distal bed — adenosine, verapamil or nitroprusside, repeated as needed.
2. Second line: a glycoprotein IIb/IIIa inhibitor, intravenous or intracoronary, when embolic or thrombotic mechanism is likely (COR 2a in the 2025 ACC/AHA ACS guideline).
3. Third line / refractory: diluted intracoronary epinephrine, particularly when the patient is normotensive or hypotensive and further vasodilatation is unsafe.
4. Adjuncts: nicorandil where available, and the SALINE technique (three rapid 10 mL saline boluses through a distally positioned aspiration catheter).
5. Selected anterior STEMI ≤6 hours: supersaturated oxygen therapy after successful stenting.

Step 4 — Reassess objectively

Repeat cTFC and MBG rather than relying on visual impression, and check ST-segment resolution at 60–90 minutes. If IMR is available, an IMR >40 after the case identifies patients who need closer heart-failure surveillance regardless of how the final angiogram looked.

Intracoronary Drug Doses for No-Reflow

The doses below follow the SCAI 2024 expert consensus dosing table, with commonly used trial ranges added. Dilute in saline and deliver distally wherever possible.

*Nitroglycerin and nicorandil are not in the SCAI table; those rows come from trial protocols and cath-lab practice.

Two practical notes. First, always place a temporary pacing wire, or at least have atropine drawn up, before giving adenosine or verapamil into a dominant right coronary artery. Second, if the patient is hypotensive, epinephrine and haemodynamic support are the rational choice — adding nitroprusside to a mean arterial pressure of 55 mmHg deepens the very perfusion-pressure problem you are trying to fix.

What the Evidence Actually Shows

Practice in this area is heavily habit-driven, and the habit does not always match the data.

A 2026 network meta-analysis in JACC: Advances pooled 13 randomised trials of intracoronary vasoactive therapy for no-reflow during primary PCI (approximately 1,674 patients; adenosine 516, epinephrine 196, nitroprusside 189, verapamil 139, control 554). Compared with control, the odds of achieving final TIMI 3 flow were:

• Verapamil OR 2.84 (95% CI 1.63–4.95)
• Epinephrine OR 2.81 (95% CI 1.72–4.58)
• Adenosine OR 1.40 (95% CI 0.91–2.15) — not significant
• Nitroprusside OR 1.02 (95% CI 0.46–2.28) — not significant

For ST-segment resolution, epinephrine (OR 4.30, 2.19–8.45), verapamil (OR 2.85, 1.64–4.96) and — in the frequentist analysis only — adenosine (OR 1.38, 1.04–1.84) all beat control; adenosine lost significance in the Bayesian sensitivity analysis. Verapamil ranked highest for final TIMI 3 flow. The authors note the irony directly: adenosine is the most widely used first-line agent, epinephrine the usual second line, and verapamil is rarely used — the reverse of the efficacy ordering. Mortality and MACE differences were not significant, so this remains surrogate-endpoint evidence.

Landmark trials at a glance

The honest summary: no pharmacological or device therapy has yet shown a mortality benefit in no-reflow. Everything above improves surrogates. Prevention still outperforms rescue.

Device and Adjunctive Strategies

Aspiration thrombectomy. Routine use is out; bailout use is in. The 2025 ACC/AHA guideline gives routine manual aspiration a Class 3 (No Benefit, LOE A), while its supporting text endorses bailout aspiration to remove thrombus that persists after balloon angioplasty or stent deployment, particularly with concomitant no-reflow — needed in an estimated 4–7% of primary PCI cases.

Distal protection devices. No benefit in native-vessel STEMI, but genuinely useful in elective degenerated saphenous vein graft intervention, where distal embolisation is the dominant mechanism.

Supersaturated oxygen (SSO₂). FDA-approved and CE-marked for non-shock anterior STEMI treated within 6 hours, delivered as a 60-minute left main infusion after stenting under the current IC-HOT-derived protocol (AMIHOT II itself used a 90-minute LAD infusion). In AMIHOT II, an all-anterior-STEMI population, the infarct-size reduction reached significance only in the pre-specified Bayesian analysis pooled with AMIHOT I.

Ischaemic postconditioning, selective intracoronary hypothermia, pressure-controlled intermittent coronary sinus occlusion, rheolytic thrombectomy, mesh-covered stents, excimer laser. All conceptually attractive, all negative or discontinued in adequately powered trials. Do not adopt them as routine.

Intracoronary fibrinolytics. The STRIVE trial randomised 210 STEMI patients with large thrombus burden to intracoronary alteplase 10 mg, 20 mg or placebo and found no benefit, with a trend toward more ventricular fibrillation during administration. Routine intracoronary lytic therapy is not supported.

What the Guidelines Say About No-Reflow

2025 ACC/AHA/ACEP/NAEMSP/SCAI ACS guideline

• Routine manual aspiration thrombectomy before PCI in STEMI: Class 3, No Benefit, LOE A. Bailout use is endorsed in the supporting text.
• GP IIb/IIIa inhibitor, IV or intracoronary, in ACS undergoing PCI with large thrombus burden, no-reflow or slow flow: Class 2a, LOE C-LD.
• Routine GP IIb/IIIa inhibitor use in ACS: Class 3, Harm, LOE B-R — lack of ischaemic benefit and increased bleeding.
• Intracoronary imaging for left main or complex lesions: Class 1, LOE A.
• Notably, the guideline contains no recommendation on intracoronary vasodilators for no-reflow. That gap is filled by expert consensus, not randomised trial-driven guidance.

2023 ESC ACS guideline

• Routine thrombus aspiration: Class III, LOE A, with text permitting aspiration for large residual thrombus after wire or balloon.
• GP IIb/IIIa antagonists should be considered for bailout if there is evidence of no-reflow or a thrombotic complication during PCI: Class IIa, LOE C.

SCAI 2024 expert consensus on primary PCI

• Use intracoronary arteriolar vasodilators delivered to the distal bed.
• Maximise coronary perfusion pressure by augmenting mean arterial pressure and reducing LVEDP.
• Grade thrombus after wire crossing; bailout aspiration for grade 4–5 thrombus is acceptable.
• Exclude coronary dissection, which can mimic no-reflow, using selective distal contrast injection.

After the Case: Monitoring, Imaging and Prognosis

Patients who develop no-reflow have larger infarcts, more adverse remodelling, more heart failure and higher mortality. Manage them as a distinct, higher-risk cohort from the moment they leave the lab.

Check ST-segment resolution at 60–90 minutes; resolution <50% signals severe microcirculatory injury. Obtain an early echocardiogram and consider cardiac MRI at 3–7 days, remembering that MVO volume roughly triples over the first 48 hours before regressing over the following weeks.

Guideline-directed heart failure therapy should be started early and titrated aggressively in these patients, and the threshold for arranging follow-up imaging and a device-therapy assessment at 40–90 days should be low.

Ten Mistakes That Turn Slow Flow Into No-Reflow

1. Grading thrombus burden before the wire crosses the lesion.
2. Injecting vasodilators through the guide catheter rather than into the distal bed.
3. Stenting into a vessel that is still TIMI 0–1 after predilatation.
4. Treating hypotension as background noise instead of as the driver of microvascular collapse.
5. Giving adenosine or verapamil into a dominant RCA without pacing backup.
6. Reaching for nitroprusside in a patient whose mean arterial pressure is already 55 mmHg.
7. Assuming TIMI 3 flow means tissue perfusion, and never recording MBG or ST-segment resolution.
8. Missing a dissection or false-lumen wire position because intravascular imaging was skipped.
9. Escalating drugs indefinitely instead of considering deferred stenting.
10. Discharging a no-reflow patient on the same pathway as an uncomplicated primary PCI.

Frequently Asked Questions About No-Reflow

What is the difference between slow flow and no-reflow? Slow flow is TIMI grade 1–2 antegrade flow after a mechanically successful PCI; no-reflow is TIMI grade 0. They lie on one continuum of microvascular obstruction, and untreated slow flow frequently progresses to no-reflow.

Which drug is the best first-line treatment for no-reflow? Convention favours intracoronary adenosine, but the 2026 network meta-analysis found verapamil and epinephrine, not adenosine, significantly improved final TIMI 3 flow. Agent choice should follow haemodynamics: vasodilators when the pressure allows, epinephrine when it does not. Delivery to the distal bed matters more than the specific drug.

How do you give intracoronary drugs distally? Advance a microcatheter, over-the-wire balloon or aspiration catheter beyond the stented segment, confirm position with a 1–2 mL selective contrast injection, then deliver the diluted agent. Randomised data show this more than doubles the rate of TIMI 3 with MBG 2–3 compared with guide-catheter injection.

Should I use aspiration thrombectomy for no-reflow? Not routinely — that carries a Class 3 (No Benefit, LOE A) recommendation with a stroke signal in TOTAL. Bailout aspiration for persistent large thrombus after balloon or stent, particularly with concomitant no-reflow, remains appropriate and is needed in roughly 4–7% of primary PCI cases.

Does no-reflow affect long-term prognosis? Yes. Microvascular obstruction on cardiac MRI is present in 57% of STEMI patients and independently predicts death or heart-failure rehospitalisation at one year, independent of infarct size.

Can no-reflow be prevented? Partially. High-dose statin loading, adequate antithrombotic preparation, short ischaemic time, careful lesion preparation, direct stenting where feasible, prophylactic distal vasodilators and deferred stenting in heavily thrombotic vessels all reduce the risk. No strategy eliminates it.

What IMR value defines significant microvascular obstruction after primary PCI? IMR >40 after primary PCI is the threshold associated with cardiac-MRI-confirmed MVO and adverse outcomes. The conventional IMR ≥25 cut-off applies to non-ACS microvascular dysfunction.

Key References

1. Rao SV, et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes. Circulation. 2025;151:e771–e862.
2. Byrne RA, et al. 2023 ESC Guidelines for the management of acute coronary syndromes. Eur Heart J. 2023;44:3720–3826.
3. SCAI Expert Consensus Statement on the Management of Patients With STEMI Referred for Primary PCI. J Soc Cardiovasc Angiogr Interv. 2024;3:102294.
4. Oliveri F, et al. Intracoronary Vasoactive Therapy for No-Reflow During Primary PCI: A Network Meta-Analysis of Randomized Trials. JACC Adv. 2026;5:102599.
5. Slow flow and no-reflow after percutaneous coronary intervention: state-of-the-art review. EuroIntervention. 2025.
6. Khan AA, et al. Intracoronary Epinephrine in the Management of Refractory No-Reflow (COAR). Circ Cardiovasc Interv. 2022;15:e011408.
7. Huang RI, et al. RECOVER: intracoronary diltiazem, verapamil and nitroglycerin for no-reflow. Am Heart J. 2012;164:394–401.
8. Jolly SS, et al. Randomized trial of primary PCI with or without routine manual thrombectomy (TOTAL). N Engl J Med. 2015;372:1389–1398.