Basics & Fundamentals
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Preexcitation Syndromes: Overview
Key Points: Pre-excitation means an accessory pathway allows atrial impulses to reach the ventricle without traversing the AV node, producing early ventricular activation. A delta wave is the defining ECG…
Delta Waves: Basics
Key Points: Definition: A delta wave is a slurred upstroke at the very start of the QRS. It reflects early ventricular activation through an accessory pathway that bypasses the AV…
WPW Syndrome and Pseudo-MI Patterns
Key Points: WPW alters ventricular depolarization, producing secondary repolarization abnormalities that can mimic or mask myocardial infarction. ST-segment deviation in WPW is often non-ischemic, driven by abnormal activation via the…
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….
ECG Basics & Fundamentals Hub
Key Points: This hub organizes the core ECG basics and fundamentals into three complementary “start here” pathways: ECG definitions and measurement, how ECGs are generated and work, and the acute…
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…
Hyperkalemia
Key Points: ECG as a Frontline Diagnostic Tool: Hyperkalemia often reveals itself on the ECG before lab confirmation. Early recognition of characteristic changes can be life-saving, especially in critically ill…
Hyperkalemia Emergencies
Key Points: Severe Hyperkalemia Mimics Several Life-Threatening Conditions: Severe hyperkalemia is one of the most dangerous ECG mimics in emergency medicine. It can resemble unstable bradyarrhythmias, VT, STEMI, and pacemaker…
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…
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