Basics & Fundamentals
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Fascicular Blocks
Key Points Definition: Delay/block within the left bundle’s fascicles—left anterior (LAF) or left posterior (LPF)—alters ventricular activation and the QRS axis. Types: LAFB (common) → left axis deviation; LPFB (rare)…
ST Segment: Basics
Key Points Definition: The ST segment runs from the J point (end of QRS) to the start of the T wave, the interval between ventricular depolarization and repolarization. Normal: Usually…
Right Ventricular Hypertrophy (RVH)
Key Points Definition: Chronic pressure/volume overload → thickened RV (pulm HTN, congenital lesions, pulmonary disease). ECG signature: Rightward axis, dominant R in V1, deep S in V5–V6, with possible right-sided…
Q Wave: Basics
Key Points Definition and Measurement: A Q wave is the first negative deflection of the QRS. Measure width in ms from the onset below baseline to its return to baseline;…
QRS Complex: Basics
Key Points: Definition and measurement: The QRS complex is ventricular depolarization, measured from the earliest ventricular deflection (Q or R) to the latest S return to baseline in any lead….
R Wave: Basics
Key Points Definition: The R wave is the first positive deflection of the QRS complex, reflecting early ventricular depolarization, predominantly of the left ventricle. Normal progression: Precordial R amplitude increases…
Hypermagnesemia
Key Points: Hypermagnesemia is usually seen in the setting of renal impairment or excessive magnesium exposure, including laxatives, antacids, bowel preps, or therapeutic magnesium infusion. The key ECG concern is…
Left Anterior Fascicular Block (LAFB)
Key Points: LAFB occurs when conduction through the left anterior fascicle is delayed or blocked. Ventricular activation travels preferentially down the left posterior fascicle, then spreads inferior-to-superior and rightward-to-leftward across…
Left Posterior Fascicular Block (LPFB)
Key Points: LPFB occurs when conduction through the left posterior fascicle is delayed or blocked. LV activation travels preferentially through the left anterior fascicle, then spreads superior-to-inferior and left-to-right toward…
PR Segment: Basics
Key Points Definition: The PR segment is the flat line from the end of the P wave to the beginning of the QRS. It reflects conduction through the AV node,…
TP Segment: Basics
Key Points Definition: The TP segment is the isoelectric interval from the end of the T wave to the start of the P wave. It reflects electrical diastole when the…
U Wave: Basics
Key Points Definition and origin: The U wave is a small deflection following the T wave, best seen in V2–V3. It likely reflects late ventricular repolarization or Purkinje repolarization. Normal…
T Wave: Basics
Key Points Definition: The T wave reflects ventricular repolarization. Measure amplitude from baseline to peak and identify the end of T to help define the QT interval. Normal appearance: Upright…
S Wave: Basics
Key Points Definition and measurement: The S wave is the first negative deflection after the R wave within the QRS. Measure depth in mm from baseline to nadir; width contributes…
Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)
Key Points: Rare, inherited ventricular arrhythmia triggered by adrenergic stress during exertion or emotion. Classically presents in children or adolescents with syncope or cardiac arrest despite a normal resting ECG…
Artifact vs Ventricular Rhythms: DDx
Key Points Artifact is a common source of misdiagnosis for serious arrhythmias such as polymorphic ventricular tachycardia (PVT), torsades de pointes, or ventricular fibrillation (VF). Always correlate the ECG findings…
Isoelectric Segment of the ECG
Key Points: The reference for ST-segment shift is the J point relative to an isoelectric baseline. The two candidates for that baseline are the TP segment and the PR segment….
Monomorphic Ventricular Tachycardia
Key Points Monomorphic ventricular tachycardia (MMVT) is the most common sustained VT. It shows a single, uniform QRS morphology throughout. Classified as sustained if lasting > 30 seconds or associated…
Inverted U Waves
Key Points Definition: A negative deflection after the T wave (a true U wave) that is ≥0.5 mm deep in a lead where the T wave is upright. Why it…
Hypokalemia
Key Points: Hypokalemia slows ventricular repolarization and alters the T–U complex before it triggers arrhythmias. Progressive pattern: T-wave flattening → prominent U waves → T–U fusion with apparent QT prolongation;…
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