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Earliest Cardiac Signs in ACS

1. ECG Changes (Minutes After Occlusion)

Hyperacute T Waves — The Earliest ECG Finding

• Tall, broad-based, and asymmetrical (unlike the symmetric tall T waves of hyperkalemia)
• ST segment may already be elevated at the J-point
• Seen in the distribution of the ischemic territory
• Transient — rapidly progresses to frank ST elevation, so often missed on the initial ECG

"The earliest electrocardiographic finding in STEMI is the hyperacute T wave... a tall and peaked structure that can appear within minutes of the interruption of blood flow." — ROSEN's Emergency Medicine

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ST-Segment Elevation (STEMI Evolution)

• Morphology evolves: flat → convex → domed ("tombstoned")
• Measured from the TP segment baseline (or PR terminal)
• Dynamic — waxes and wanes with symptoms (distinguishes from benign causes)
• ST elevation is a consequence of currents of injury from ischemia lowering resting membrane potential in the affected zone

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ST Depression — NSTEMI / Subendocardial Ischemia

• Seen in unstable angina and NSTEMI
• Typically horizontal or downsloping (upsloping is less specific)
• May also precede ST elevation in evolving STEMI
• Diffuse ST depression + ST elevation in aVR → severe ischemia (left main or proximal LAD occlusion equivalent)

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STEMI Equivalents — Critical Patterns Not to Miss

• Type A: Biphasic T waves in V2–V3 (25% of cases)
• Type B: Deeply inverted T waves in V2–V3 (75% of cases)
• Patient is often pain-free at the time of ECG — but the lesion is critical
• Can progress to massive anterior STEMI within hours

• ST depression at the J-point + prominent upward T waves in precordial leads
• • ST elevation in aVR
• Treated as a STEMI equivalent — may not progress to classic ST elevation but represents total/near-total LAD occlusion

• No direct ST elevation on standard 12-lead
• Presents as ST depression + tall R wave in V1–V3
• Confirmed with posterior leads V7–V9

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T-Wave Inversions

• Classically narrow and symmetrical in ACS (unlike broad asymmetric post-MI inversions)
• May represent subacute/evolving ischemia
• Pseudonormalization — a previously inverted T wave that appears "normal" during chest pain is an ischemic sign

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Q Waves — Late Finding

• Represent irreversible myocardial necrosis
• May appear within the first hour of infarction, but most commonly develop at 8–12 hours
• Their presence does NOT preclude emergent reperfusion — treat based on clinical history and symptoms

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2. Cardiac Biomarkers (Hours After Infarction)

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Summary: Chronological Sequence of Earliest Signs

Minutes 0–30:     Hyperacute T waves (ECG)
Minutes 30–60:    ST-segment elevation (STEMI) or ST depression (NSTEMI/UA)
Hours 1–3:        High-sensitivity troponin begins to rise
Hours 1–12:       T-wave inversions (evolving ischemia or post-reperfusion)
Hours 8–12:       Pathologic Q waves develop (necrosis complete)

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Cardiac Examination Findings in ACS

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General Appearance & Vital Signs

"If the patient has a large area of myocardial ischemia or a large NSTEMI, the physical findings can include diaphoresis; pale, cool skin; sinus tachycardia; a third and/or fourth heart sound; basilar rales; hypotension; and in severe cases, cardiogenic shock." — Harrison's Principles of Internal Medicine 22E

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Jugular Venous Pressure (JVP)

• Elevated JVP → Left heart failure with raised filling pressures; or RV infarction
• RV infarction triad (complicates inferior MI): hypotension + elevated JVP + clear lung fields
• Kussmaul's sign (JVP rises on inspiration) may be present in RV infarction

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Precordial Examination

Inspection & Palpation

• Dyskinetic apical impulse — paradoxical outward movement of infarcted segment during systole; indicates large anterior wall MI / LV aneurysm
• Displaced apex beat — suggests LV dilatation from prior infarction or acute severe dysfunction
• May be normal in small infarcts

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Auscultation — Heart Sounds

S1 and S2

• Soft S1 — reduced contractility of the ischemic myocardium reduces mitral valve closing force
• Paradoxical splitting of S2 — if LBBB or severe LV dysfunction delays aortic valve closure

S4 Gallop (Atrial Gallop) — Very Common

• Present due to reduced LV compliance from ischemia/infarction
• Heard in late diastole (pre-systole), best at the apex with the bell
• Can be normal in elderly individuals, so less specific in isolation
• Represents atrial kick into a stiff, non-compliant ventricle

S3 Gallop (Ventricular Gallop) — Significant Finding

• Heard in early diastole — due to rapid passive filling of a volume-overloaded or poorly compliant ventricle
• Indicates significant LV dysfunction / heart failure
• Low-pitched, best at apex in left lateral decubitus position
• Associated with higher Killip class and worse prognosis

"The presence of an S3 gallop is useful for detecting left ventricular [dysfunction]" — Goldman-Cecil Medicine

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Auscultation — Murmurs

New Systolic Murmur — Always Pathological in ACS Context

"Papillary muscle rupture occurs in approximately 1% of patients with AMI, is more common with inferior myocardial infarction, and usually occurs 3 to 5 days after AMI." — Tintinalli's Emergency Medicine

Soft or Absent Murmur — Do Not Be Falsely Reassured

• In secondary (ischemic) MR, the murmur can be soft and underwhelming despite severe regurgitation, due to reduced ventricular contractility and large regurgitant orifice
• A new murmur + hemodynamic deterioration mandates urgent echo regardless of murmur intensity

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Auscultation — Pericardial Rub

• Pericardial friction rub — appears 12 hours to 10 days post-MI (early pericarditis — Dressler-related or direct extension)
• Scratchy, to-and-fro sound; louder on leaning forward
• Three-component rub (systolic, early diastolic, presystolic) is pathognomonic
• In STEMI, early pericarditis (direct) occurs within 24–72 hours over the infarct zone

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Lung Examination

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Peripheral Examination

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Killip Classification — Examination-Based Prognostic Staging

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Summary Table

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