Periprocedural Myocardial Infarction After PCI and CABG

Definition and pathophysiology

Periprocedural myocardial infarction (MI) is myocardial necrosis temporally related to coronary revascularization. It may follow percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG), and is classified within the universal MI framework as follows:

• Type 4a MI: MI related to PCI.

• Type 4b MI: MI caused by stent thrombosis.

• Type 4c MI: MI associated with in-stent restenosis.

• Type 5 MI: MI related to CABG.

Type 4b and type 4c events fulfil the criteria for type 1 MI. Procedural myocardial injury may also occur without satisfying the diagnostic threshold for periprocedural MI. This distinction is clinically important because cardiac troponin elevation after revascularization is common and may reflect procedural myocardial injury rather than a clinically significant infarction.

Mechanisms of injury

Procedural injury may result from acute compromise of coronary flow. Mechanisms include:

• Coronary dissection with obstruction of the true lumen

• Occlusion of a major epicardial artery or bypass graft

• Side-branch occlusion or thrombus

• Disruption of collateral flow

• Distal embolization

• Stent thrombosis

• Graft occlusion after CABG

• No-reflow despite removal of an apparent epicardial stenosis

The clinical consequences depend on the amount of viable myocardium supplied by the affected vessel and the adequacy of collateral circulation. Abrupt loss of flow may cause rapid deterioration when a large myocardial territory is jeopardized. Cardiovascular collapse after failed PCI is more likely with extensive myocardium at risk, severe baseline stenosis, multivessel coronary artery disease, or diffuse disease.

No-reflow represents impaired antegrade myocardial perfusion in the absence of a flow-limiting epicardial stenosis. It is associated particularly with intervention on degenerated saphenous vein grafts, rotational atherectomy, and acute MI procedures. Distal embolization of atheromatous or thrombotic material is an important proposed mechanism. No-reflow may produce major short- and long-term adverse consequences, including a substantially increased risk of periprocedural MI and death.

Troponin elevation and myocardial injury

Cardiac troponin elevation following PCI or CABG may indicate procedural myocardial injury. Late gadolinium enhancement cardiac magnetic resonance imaging has demonstrated procedural injury in patients undergoing either procedure, and postprocedural cTnI elevation correlates with evidence of injury on cardiac magnetic resonance.

Interpretation is more difficult when the baseline troponin is already elevated, as occurs during acute MI. If the preprocedural concentration is above the 99th percentile upper reference limit, it must be stable or falling before a subsequent rise can reliably be attributed to acute procedural injury. Even then, it may not be possible to determine precisely how much of the postprocedural increase results from the index MI and how much is related to the intervention.

Diagnostic criteria

General principles

For events occurring within 48 hours of the index procedure, diagnosis requires both:

• A defined postprocedural troponin rise, with thresholds differing for PCI and CABG; and

• At least one additional indicator of new myocardial ischemia or procedural coronary compromise.

When preprocedural troponin is elevated but stable or falling, the postprocedural level must demonstrate both the required absolute threshold and a rise of more than 20% from baseline.

Type 4a MI after PCI

In a patient with normal baseline cTn, type 4a MI is defined by:

• cTn greater than 5 times the 99th percentile upper reference limit; and

• At least one of the following:

If baseline cTn is elevated but stable or falling, the postprocedural cTn must rise by more than 20%, while also exceeding 5 times the 99th percentile upper reference limit.

New pathological Q waves alone may fulfil the type 4a definition when cTn is elevated and rising but remains below the prespecified biochemical threshold.

Type 5 MI after CABG

For CABG, type 5 MI is defined by:

• cTn greater than 10 times the 99th percentile upper reference limit in a patient with normal baseline cTn; and

• At least one of the following:

When baseline cTn is elevated but stable or falling, a rise of more than 20% is required in addition to an absolute postprocedural value above 10 times the 99th percentile upper reference limit.

Isolated new pathological Q waves can satisfy the type 5 definition when cTn is elevated and rising but does not reach the specified threshold.

Clinically relevant post-PCI MI

A more stringent SCAI definition identifies clinically relevant post-PCI MI using either:

• CK-MB at least 10 times the upper limit of normal; or

• cTn I or T at least 70 times the upper limit of normal.

A lower biomarker threshold may be used when accompanied by new pathological Q waves in at least two contiguous ECG leads or new left bundle branch block:

• CK-MB at least 5 times the upper limit of normal; or

• cTn at least 35 times the upper limit of normal.

These alternative definitions should not be conflated with the universal definition, as their thresholds and accompanying requirements differ.

Clinical presentation

Periprocedural MI may be clinically apparent or silent. Clinical manifestations include:

• Recurrent or persistent chest pain

• New ischemic ECG abnormalities

• Hemodynamic compromise

• Ventricular failure

• Electrical instability or life-threatening arrhythmia

• Sudden deterioration due to abrupt vessel closure, perforation, or no-reflow

After PCI, chest pain is relatively common and does not by itself establish recurrent ischemia or MI. Nevertheless, it requires immediate assessment because recurrent ischemia may result from acute or subacute stent thrombosis, residual dissection, plaque prolapse, side-branch occlusion, thrombus at the treatment site, or untreated residual coronary disease.

After CABG, the presentation may be obscured by postoperative pain, sedation, or concurrent hemodynamic disturbances. A marked troponin rise is particularly concerning when accompanied by difficulty separating from cardiopulmonary bypass, technically challenging anastomoses, perioperative evidence of ischemia, or other operative complications.

Evaluation and physical examination

The initial assessment should establish:

• Timing and nature of symptoms relative to PCI or CABG

• Presence of recurrent ischemic pain

• Hemodynamic stability

• Evidence of ventricular failure

• Electrical instability or arrhythmia

• Potential procedural or operative complications

• Preprocedural troponin concentration and its trajectory

Physical examination should focus on signs of hemodynamic compromise, heart failure, and complications that may accompany procedural ischemia. After PCI, rapid deterioration may accompany coronary perforation, which can lead to cardiac tamponade and collapse within minutes. After CABG, periprocedural MI has particular prognostic importance when associated with hemodynamic or arrhythmic complications or pre-existing LV dysfunction.

A new pericardial effusion after MI or intervention also affects antithrombotic management. In the setting of postinfarction pericarditis, an effusion at least 1 cm in size or an enlarging effusion should generally prompt discontinuation of anticoagulation, unless there is a strong indication to continue it; in such cases, close monitoring for tamponade and careful assessment of clotting parameters are required.

Diagnostics

Electrocardiography

A 12-lead ECG is the immediate investigation for chest pain after PCI. New ischemic ECG changes support a diagnosis of type 4a MI when the relevant troponin threshold is met. New pathological Q waves are evidence of myocardial injury after either PCI or CABG and may independently satisfy the procedural MI definition when troponin is elevated and rising but remains below the formal biochemical threshold.

New left bundle branch block is included in the more stringent SCAI definition when accompanied by the specified biomarker rise.

Coronary angiography

When recurrent ischemia is suspected after PCI, coronary angiography is the most expeditious method of identifying the cause. It may demonstrate:

• Acute or subacute stent thrombosis

• Residual or propagated dissection

• Major-vessel occlusion

• Side-branch occlusion

• Thrombus at the treatment site

• Distal embolization

• No-reflow

• Residual untreated disease

After CABG, angiography may demonstrate new graft occlusion or native coronary occlusion, either of which supports type 5 MI when the biomarker threshold and other diagnostic criteria are met.

Echocardiography and other imaging

Imaging evidence supporting procedural MI includes:

• New loss of viable myocardium

• New regional wall-motion abnormality in an ischemic distribution

Cardiac magnetic resonance with late gadolinium enhancement can demonstrate procedural myocardial injury following PCI or CABG. It is particularly useful for identifying myocardial injury when the interpretation of biomarker changes is uncertain, although the source material does not specify a routine diagnostic protocol.

Biomarkers and laboratory findings

Cardiac troponin

Troponin is central to the diagnosis, but interpretation depends on:

• The procedure performed

• The baseline cTn concentration

• Whether the baseline value is stable, rising, or falling

• The absolute postprocedural value

• The presence of corroborating ECG, imaging, or angiographic findings

The relevant thresholds are summarized below.

A troponin rise without supporting ischemic, imaging, or angiographic evidence represents procedural myocardial injury rather than definite periprocedural MI. Marked isolated cTn elevation after CABG, even without the other formal criteria, indicates prognostically important procedural injury.

Assay-specific interpretation is essential. After CABG, reported postoperative cTnI concentrations may be substantially higher than cTnT concentrations, emphasizing that thresholds cannot be transferred between assays without consideration of the assay used.

CK-MB

Asymptomatic CK-MB elevation below 5 times the upper limit of normal occurs after a technically successful PCI in approximately 3%–11% of cases and has little apparent clinical consequence. Larger degrees of myonecrosis are associated with higher one-year mortality and should be considered clinically significant in the appropriate context.

Troponin elevations occur more frequently than CK-MB elevations after PCI, but the incremental prognostic value of troponin over CK-MB elevation is less clearly established in the source material. Spontaneous MI after PCI has greater prognostic importance than isolated periprocedural enzyme elevation.

After CABG, the diagnostic criteria are based primarily on cardiac troponin or CK-MB more than 10 times the upper limit of normal together with new Q waves, objective new myocardial dysfunction, or graft occlusion demonstrated by imaging or angiography.

Procedural complications associated with periprocedural MI

Coronary dissection

Deep extension of a coronary dissection into the media or adventitia may compromise the true lumen and cause ischemia. Most intraprocedural dissections can be treated promptly with stenting, but significant residual dissection remains clinically important. It increases the risk of postprocedural MI, emergency CABG, stent thrombosis, and mortality.

Coronary perforation

Perforation occurs in approximately 0.2%–0.5% of PCI procedures and is more common with atheroablative devices and hydrophilic wires than with balloon angioplasty or conventional guidewires. Depending on the rate of extravasation, tamponade and hemodynamic collapse may develop within minutes. Immediate recognition and treatment are essential.

No-reflow

No-reflow occurs in up to 2%–3% of PCI procedures. It is associated with a markedly higher risk of periprocedural MI and death. Intracoronary sodium nitroprusside and other pharmacological approaches have been used, but their efficacy in reducing subsequent adverse events remains debated.

Abrupt closure and stent thrombosis

Although coronary stents have reduced the frequency of abrupt closure, acute loss of flow may still occur because of dissection, thrombus, side-branch occlusion, distal embolization, or perforation. Stent thrombosis after discharge can produce severe clinical sequelae according to the amount of myocardium supplied by the stented artery.

Graft failure after CABG

New graft occlusion is a defining angiographic element of type 5 MI when accompanied by the relevant troponin rise. Late graft disease is also a major cause of recurrent symptoms and reoperation. In patients with saphenous vein graft failure requiring repeat revascularization, PCI of the native coronary artery is preferred when feasible because of lower complication rates and better long-term patency than SVG PCI.

Treatment and management

Management depends on whether the event represents uncomplicated biomarker elevation, clinically significant procedural myocardial injury, or an acute ischemic complication requiring urgent revascularization.

Immediate management after PCI

New chest pain after PCI requires immediate 12-lead ECG assessment. When recurrent ischemia is suspected, urgent coronary angiography should be performed to identify and treat the underlying cause. The likely mechanisms include stent thrombosis, residual dissection, plaque prolapse, side-branch occlusion, thrombus, distal embolization, no-reflow, or untreated residual disease.

The source material emphasizes that emergency or urgent CABG after PCI is now uncommon. It is reserved for catastrophic complications such as coronary perforation, severe dissection, or abrupt closure when the situation cannot be adequately managed percutaneously.

Immediate management after CABG

A marked postoperative troponin rise should be interpreted in the context of:

• New ECG abnormalities

• New regional dysfunction or loss of viable myocardium

• Graft or native coronary occlusion

• Difficulty separating from bypass

• Technically difficult anastomoses

• Perioperative evidence of ischemia

• Hemodynamic or arrhythmic complications

Such findings should prompt clinical review of the operation and consideration of additional diagnostic testing for type 5 MI.

Emergency revascularization

When a procedural complication causes ongoing ischemia, hemodynamic compromise, or threatened occlusion of a vessel supplying substantial myocardium, urgent revascularization is required when feasible.

After failed PCI in NSTE-ACS, emergency CABG is reasonable when there is ongoing ischemia, hemodynamic compromise, or threatened occlusion of an artery supplying substantial myocardium and the patient is an appropriate surgical candidate.

Emergency CABG should not be performed after failed primary PCI when there is no ischemia or large myocardial territory at risk, or when surgery is not technically feasible because of no-reflow or poor distal targets.

In STEMI, emergency or urgent CABG may be effective when PCI is not feasible or unsuccessful and a large area of myocardium remains at risk. PCI remains beneficial in STEMI complicated by ongoing ischemia, acute severe heart failure, or life-threatening arrhythmia irrespective of the time from symptom onset.

Antithrombotic treatment after PCI

PCI is performed with antithrombotic therapy to reduce coronary thrombus formation. The source material identifies:

• Aspirin

• A P2Y12 antagonist

• An antithrombin agent

After drug-eluting stent implantation:

• Aspirin should be continued indefinitely.

• A P2Y12 antagonist is ideally continued daily for one year.

Continuation of dual antiplatelet therapy for as long as 30 months may provide additional benefit but increases bleeding risk. Shorter treatment courses may be appropriate in patients at high bleeding risk or those requiring long-term oral anticoagulation.

If antiplatelet treatment must be interrupted, the case should be reviewed with the PCI operator and a coordinated plan developed. Interruption should be as brief as clinically acceptable because stent-thrombosis risk is influenced by stent dimensions, lesion complexity, diabetes, age, procedural technique, adherence, and individual response to platelet inhibition.

After CABG performed for acute coronary syndrome, dual antiplatelet therapy should be resumed and continued for 12 months in patients without a long-term indication for oral anticoagulation.

Postinfarction pericarditis

Pericarditis may occur from the first day to as late as eight weeks after STEMI. Pain is more suggestive of pericarditis when it radiates to the trapezius ridge, worsens with inspiration, and improves on sitting forward.

Early after STEMI, traditional treatment consists of aspirin at doses higher than routine postinfarction dosing, such as 650 mg orally as often as every four hours, together with a proton pump inhibitor for two to four weeks. Colchicine is increasingly used as adjunctive treatment and is recommended in recent guidance for late pericarditis, defined in the source material as occurring more than one week after infarction, for at least three months.

Nonsteroidal anti-inflammatory drugs and corticosteroids should be avoided early after infarction because they may interfere with myocardial healing. Anticoagulation increases the risk of hemorrhagic pericarditis, although the presence of a pericardial rub alone does not absolutely prohibit anticoagulant therapy.

Choosing PCI or CABG after procedural complications

The choice between repeat PCI and CABG should be individualized through a multidisciplinary heart-team approach involving interventional cardiology and cardiac surgery.

Factors favouring CABG

CABG is favoured by:

• Diabetes

• LVEF below 35%

• Contraindication to dual antiplatelet therapy

• Diffuse in-stent restenosis

• Severe coronary calcification

• Inability to achieve complete revascularization with PCI

• Concomitant need for valve or aortic surgery

• Complex multivessel coronary disease

• Significant left main disease in appropriate surgical candidates

In stable ischemic disease with multivessel coronary disease and severe LV systolic dysfunction, defined as LVEF below 35%, CABG is recommended to improve survival. CABG is also recommended for significant left main stenosis, while PCI may be reasonable in selected patients when it can provide an equivalent degree of revascularization.

Factors favouring PCI

PCI offers lower initial morbidity, more rapid recovery, a lower risk of stroke than CABG, and avoidance of surgical recovery. It is frequently used for one- or two-vessel disease and selected three-vessel or left main disease. However, compared with CABG, PCI is associated with more repeat revascularization, less complete revascularization, and somewhat less relief of angina.

For complex multivessel disease, especially when diabetes is present, CABG generally provides more favourable long-term outcomes than PCI. In less complex disease, particularly with a SYNTAX score of 22 or less, PCI outcomes may be comparable to CABG in appropriately selected patients.

Guideline recommendations

The principal recommendations relevant to periprocedural MI and urgent management are summarized below.

Prognosis

Overall mortality after PCI is approximately 1%, but is higher in patients with STEMI, cardiogenic shock, or previously poor LV function when a coronary occlusion develops.

The prognostic significance of postprocedural biomarker elevation depends on its magnitude and clinical context. Small, asymptomatic CK-MB elevations are common and generally have little apparent clinical consequence. Larger degrees of myocardial necrosis are associated with higher one-year mortality. Spontaneous MI after PCI carries greater prognostic importance than isolated periprocedural enzyme elevation.

Periprocedural MI after CABG has an adverse effect on both early and late prognosis, particularly when accompanied by hemodynamic or arrhythmic complications or pre-existing LV dysfunction. The incidence varies substantially according to the diagnostic definition used, and biomarker elevation alone may represent significant procedural injury without meeting the formal criteria for type 5 MI.

Residual coronary dissection, no-reflow, acute occlusion, and graft failure are associated with worse outcomes. Following PCI, repeat revascularization is more common than after CABG. Following CABG, reoperation carries greater mortality than an initial operation, and late saphenous vein graft disease is a major indication for redo surgery.

Follow-up

Follow-up should address:

• Recurrent chest pain or ischemic symptoms

• Adherence to antiplatelet therapy

• Bleeding risk and any need to interrupt treatment

• Heart failure or LV dysfunction

• Recurrent arrhythmia

• Renal dysfunction after CABG

• Neurologic complications after surgery

• Recurrent or progressive native-vessel disease

• Graft or stent failure

After PCI, adherence to dual antiplatelet therapy is particularly important because premature interruption and inadequate platelet inhibition increase the risk of stent thrombosis. Any required interruption should be coordinated with the interventional operator.

After CABG, postoperative surveillance should recognize that atrial fibrillation is common, frequently occurring within the first two to three days. Beta-blockers reduce its frequency and should be administered before and after CABG when there are no contraindications. Amiodarone may be considered for prophylaxis in patients at high risk. When postoperative AF occurs, rate control and rhythm control have not differed in hospitalization duration, complications, or AF rates; many patients revert spontaneously to sinus rhythm within 24 hours.

The source material does not define a universal imaging or biomarker surveillance schedule after periprocedural MI. Follow-up testing should therefore be guided by symptoms, ventricular function, ECG findings, suspected recurrent ischemia, and the clinical circumstances of the original procedural event.