Emergency Medicine Hub / Cardiovascular Emergencies • 3 min read • 3 sections

SCAD & Mechanical Complications of Acute Myocardial Infarction

Recognition and emergency management of Spontaneous Coronary Artery Dissection (SCAD: Yip-Saw classification, fibromuscular dysplasia, pregnancy-associated ACS) and catastrophic post-infarction mechanical complications (papillary muscle rupture, acute ventricular septal rupture, and left ventricular free wall rupture).

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

Suspect SCAD

Young female (<50 years old), postpartum, minimal/no atherosclerotic risk factors, presenting with classic ACS symptoms, elevated troponin, and ST elevations or depressions.

SCAD Primary Strategy

Conservative medical management (aspirin, beta-blocker, heparin initially; discontinue heparin once SCAD confirmed on angiography). Avoid routine stenting/PCI unless ongoing hemodynamic instability or total vessel occlusion, as balloon angioplasty frequently propagates false lumen dissection.

Screen for Fibromuscular Dysplasia (FMD)

>50% of SCAD patients have underlying extracranial arteriopathy; obtain outpatient CTA/MRA of renal, iliac, and cerebrovascular vessels.

Post-MI Papillary Muscle Rupture

Occurs 2 to 7 days post-MI (posteromedial papillary muscle supplied solely by PDA, usually inferior MI). Acute onset pulmonary edema, cardiogenic shock, and soft/harsh apical holosystolic murmur. Emergent bedside echo -> IABP/Impella -> urgent cardiac surgery.

Post-MI Ventricular Septal Rupture (VSD)

Occurs 3 to 5 days post-MI. Harsh holosystolic murmur with palpable thrill at left lower sternal border; step-up in oxygen saturation from RA to RV (>10%). Emergent surgical patch repair.

Post-MI Free Wall Rupture

Occurs 3 to 14 days post-MI. Sudden acute cardiac tamponade, PEA arrest, Beck's triad. Emergent pericardiocentesis as temporizing bridge to emergency thoracotomy/OR.

Bottom-Line Clinical Pearl

SCAD is the leading cause of pregnancy-associated myocardial infarction and causes up to 35% of ACS in women under 50 with no traditional cardiovascular risk factors. Management is CONSERVATIVE medical therapy in stable patients, as PCI carries severe risk of propagating the intramural hematoma. Post-MI new harsh holosystolic murmur with shock signals a mechanical rupture requiring emergent surgical repair.

CRITICAL PEARL: Why SCAD is NOT Managed Like Atherosclerotic ACS

In conventional atherosclerotic plaque rupture, urgent PCI with balloon angioplasty and stenting is standard of care. In SCAD, the coronary wall is fragile and dissects easily; catheter-based instrumentation carries a failure rate > 50% and causes extension of the dissection plane and occlusion of side branches. Conservative medical management is the preferred first-line therapy in hemodynamically stable patients without left main dissection, as >70-90% heal spontaneously within 30 days.

Post-Myocardial Infarction Mechanical Catastrophes

Complication	Timing Post-MI	Culprit Vessel/Anatomy	Clinical Presentation & Murmur	Emergency Diagnostics & Management
Acute Papillary Muscle Rupture	2 to 7 days (peak day 3-5)	RCA (inferior MI) supplying posteromedial muscle (single blood supply)	Sudden flash pulmonary edema, cardiogenic shock; soft/harsh holosystolic murmur radiating to axilla (may be absent in severe shock)	Bedside POCUS shows hyperdynamic LV, flail mitral valve leaflet, massive eccentric MR jet. Vasodilators (nitroprusside), IABP/Impella, emergent mitral valve replacement
Ventricular Septal Rupture (VSD)	3 to 5 days	LAD (apical VSD) or RCA (basal posterior VSD)	Biventricular failure, cardiogenic shock; loud, harsh holosystolic murmur with palpable thrill at LLSB	Echocardiogram reveals left-to-right shunt; right heart catheterization demonstrates oxygen saturation step-up >= 10% from RA to RV. Afterload reduction, IABP, emergent surgical closure
Left Ventricular Free Wall Rupture	3 to 14 days (peak day 5-7)	LAD or RCA; transmural infarction, older females, first MI, delayed presentation	Sudden catastrophic collapse, chest pain, syncope, profound hypotension, PEA arrest, Beck's triad (elevated JVD, muffled heart sounds, hypotension)	Bedside POCUS shows large hemopericardium with tamponade physiology (diastolic RV collapse). Emergency subxiphoid pericardiocentesis to relieve tamponade; immediate open thoracotomy/OR repair

Angiographic Yip-Saw Classification of SCAD

Type 1 (Pathognomonic Dissection): Contrast staining of vessel wall with multiple radiolucent lumens and longitudinal flap.
Type 2 (Diffuse Smooth Stenosis: Most Common, 60–70%): Smooth, diffuse narrowing (typically >20 mm length) without a visible flap; easily misdiagnosed as vasospasm or normal caliber vessel if intracoronary nitroglycerin is not given.
Type 3 (Mimicking Atherosclerosis): Focal or tubular stenosis (<20 mm) resembling conventional atherosclerotic stenosis; requires intravascular imaging (OCT or IVUS) to visualize intramural hematoma.

Clinical Pitfalls

Discharging young women with chest pain without ECG/troponin: SCAD patients are typically young, athletic females without hypertension, hyperlipidemia, or smoking history; never dismiss chest pain based on absent Framingham risk factors.
Assuming absence of murmur rules out papillary muscle rupture: In acute severe mitral regurgitation, rapid equalization of left ventricular and left atrial pressures can render the murmur completely silent! Look for unexplained pulmonary edema post-MI.

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