Basics & Fundamentals
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WPW with Antidromic SVT (Antidromic AVRT)
Key Points: Antidromic AVRT is an AV re-entrant tachycardia that conducts antegrade down the accessory pathway and returns retrograde through the AV node (or another pathway), producing a regular wide-complex…
WPW with Orthodromic SVT (Orthodromic AVRT)
Key Points: Orthodromic AVRT is the most common tachyarrhythmia in WPW and presents as a regular narrow-complex SVT that is indistinguishable from AVNRT during the tachycardia. Mechanism: antegrade conduction down…
ECG Foundations: Vectors, Leads, & Activation
Key Points: An ECG records voltage differences over time. The ECG tracing is a plot where the horizontal axis is time and the vertical axis is voltage. Leads are viewpoints….
P Wave: Basics
Key Points: Definition and measurement: The P wave is atrial depolarization. Measure duration from initial deflection to return to baseline and amplitude from baseline to peak. Normal values: Duration <120…
Non-Thrombotic Causes of Acute Coronary Syndrome (ACS)
Key Points: ACS ≠ Always Thrombosis: While most ACS is due to plaque rupture with thrombus formation, several important non-thrombotic causes can produce identical ECG changes, troponin elevation, and symptoms….
Occlusion MI: STEMI Criteria & Beyond
Key Points: The ECG’s primary role in ACS is detecting acute coronary occlusion. Acute coronary occlusion myocardial infarction (OMI) is a time-critical diagnosis that requires immediate reperfusion. Time is myocardium….
QT Interval: Basics
Key Points: Definition: QT is measured from QRS onset to T-wave end. It reflects total ventricular depolarization plus repolarization. Use QTc: QT varies with heart rate. Interpret QTc, not the…
JT Interval: Basics
Key Points: The JT interval isolates ventricular repolarization by removing QRS duration from the QT. JT = QT − QRS. It is most useful when the QRS is wide, where…
PR Interval: Basics
Key Points: Definition: PR interval runs from P-wave onset to the first ventricular deflection (start of QRS). It reflects atrial depolarization plus conduction through the AV node and His-Purkinje system….
RR Interval: Basics
Key Points: The RR interval is the time between consecutive R waves. It is the most practical way to assess rate and regularity. RR is the backbone of rhythm interpretation:…
Waveforms, Segments, & Intervals: Basics
Key Points: Every ECG tracing is built from waveforms (deflections), segments (baseline portions between waveforms), and intervals (time that include waveforms plus segments). Waveforms describe electrical events (depolarization or repolarization)….
Hypocalcemia
Key Points: Prolonged QTc is the hallmark ECG change in hypocalcemia, driven mainly by ST-segment prolongation with relatively normal T-wave shape. Hypocalcemia can increase arrhythmia risk, including TdP, but TdP…
Hypercalcemia
Key Points: Shortened QTc interval is the hallmark ECG clue in hypercalcemia, primarily due to a shortened ST segment duration. Hypercalcemia can mimic acute STEMI on ECG (pseudoinfarction pattern due…
ECG Findings of LV Aneurysm
Key Points: Definition: A true LV aneurysm is a chronic, post transmural MI complication from scarred myocardium with akinetic or dyskinetic (paradoxical) wall motion. ECG hallmark: Persistent ST elevation in…
Acute Pericarditis
Key Points: Acute pericarditis commonly mimics ACS clinically and on ECG, creating frequent diagnostic uncertainty in acute care. The first priority is excluding occlusion MI. Pericarditis should be considered only…
Early Repolarization
Key Points: Historical View: Early repolarization (ER) was long considered a benign cause of ST elevation, often called benign early repolarization (BER). Modern View: Certain ER patterns, now termed malignant…
Post-Thrombolytic Reperfusion ECG Findings
Key Points Reperfusion after fibrinolysis is a bedside diagnosis using a bundle of findings: symptoms, ECG trend, and hemodynamic/electrical stability. Best ECG marker of successful fibrinolysis: at least 50% ST-segment…
ECG Evidence of Reperfusion After Occlusion
Key Points: Reperfusion and re-occlusion can occur spontaneously or after therapy. The ECG often reflects these changes earlier than symptoms. Most useful bedside ECG marker of reperfusion is ST-segment resolution…
Early Reciprocal Changes: OMI Pattern
Key Points: STEMI criteria alone miss some acute coronary occlusions, so look for subtle “occlusion clues,” not just traditional STEMI criteria cutoffs. Minor ST elevation under 1 mm paired with…
Acute Coronary Syndromes (ACS)
Key Points: ACS is a clinical syndrome: classified by ischemic symptoms + ECG + troponin. ACS exists on a continuum of unstable angina, NSTEMI, STEMI, and patients can evolve between…
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