ECG Anatomy Series

ECG heart rate calculation methods — 300 rule, 1500 rule, 6-second method, tachycardia, bradycardia, irregular rhythms, and clinical significance.

Mean frontal plane QRS vector interpretation — normal and pathological axis deviations, systematic determination methods, and clinical correlations.

The path the impulse takes from the SA node to the myocardium, and the paper speed that sets every ECG measurement.

Artifact can mimic VF and reversed leads can mimic infarct: check the pulse and leads, but never delay care for unstable VT

Atrial depolarization and P wave morphology — normal variants, abnormalities, atrial enlargement patterns, and ectopic atrial rhythms.

Initial ventricular depolarization and MI marker — physiologic vs pathologic Q waves, criteria, MI localization, and Q wave mimics.

Ventricular depolarization and R wave progression — normal amplitude, dominant R in V1/aVR, poor progression, posterior MI, and RVH.

Terminal ventricular depolarization — deep S waves in LVH/RVH, Sokolow-Lyon criteria, bundle branch patterns, and S1S2S3 pattern.

Ventricular repolarization morphology — tall/peaked T waves, inversions, Wellens syndrome, hyperacute changes, and electrolyte effects.

Isoelectric baseline between atrial and ventricular depolarization — PR depression in pericarditis, atrial infarction, and STEMI differentiation.

AV conduction time measurement — normal PR duration, first-degree AV block, short PR syndromes, and preexcitation patterns.

Ventricular depolarization patterns — QRS duration/morphology, bundle branch blocks, hypertrophy criteria, and conduction delays.

Ventricular repolarization abnormalities — ST elevation/depression, T wave inversions, ACS patterns, and repolarization variants.

Ventricular systole duration — QT measurement, QTc correction, prolonged/shortened QT causes, Torsades risk, and drug effects.

Supraventricular arrhythmias — atrial fibrillation, atrial flutter, MAT, atrial tachycardia, and PACs with diagnostic criteria.

Life-threatening ventricular arrhythmias — VT, VF, PVCs, AIVR, and Brugada criteria for VT diagnosis.

The sinus node sets the pace; when it slows, pauses or fails, the escape rhythm and the patient's perfusion decide what to do now

Junctional rhythms from escape to tachycardia: the rate names the rhythm, and digoxin toxicity is the cause that cannot be missed.

Narrow-complex SVT is usually re-entry: vagal maneuvers, then adenosine when stable; an irregular wide rhythm needs a different plan.

A regular wide QRS is VT until proven otherwise, and the wrong drug in pre-excited AF can cause VF

Recognizing VF, pulseless VT, PEA and asystole decides whether to shock, give epinephrine or keep doing CPR.

A pacing spike is not a heartbeat: check capture, sensing and ICD shocks before you trust the rhythm

AV blocks and intraventricular conduction delays — 1st/2nd/3rd-degree AV blocks, RBBB, LBBB, fascicular blocks, and pacing implications.

Pre-excited AF is irregular and wide: AV nodal blockers can drive it into VF, so know which tachycardias they are safe for.

Read every ECG in the same six steps: rate, rhythm, axis, intervals, morphology, then ST-T waves compared with a prior tracing.

Which leads show the occluded wall, what the reciprocal leads add, and when to repeat the 12-lead

Occlusion patterns that look nothing like classic STEMI, and what to do before the cath lab call

Potassium, calcium and magnesium shifts change the ECG before labs return; a normal tracing does not exclude hyperkalemia.

Voltage and P-wave rules for LVH, RVH and atrial enlargement, and why LVH strain can look like a heart attack.

Inferior STEMI with RV involvement: why V4R matters and why nitrates can drop the blood pressure

Sgarbossa criteria flag acute occlusion when LBBB or a paced QRS hides the usual STEMI thresholds

Five ECG patterns that look like STEMI, and the features that separate them before the cath lab call.

Wide QRS, digoxin effect and QT prolongation from poisons: what the ECG shows and what to give first

Brugada, long QT, pre-excitation, ARVC and HCM patterns that signal sudden-death risk after a syncopal episode