ECG rhythms

Each page shows the rhythm on a moving monitor, computed by the TracingsMD heart model, and lets you run it live on the engine and, for most rhythms, change its rate. It explains what the rhythm is, how to read it, its causes, what to consider and what it can be confused with.

Sinus rhythms

• Normal sinus rhythm

  The normal heart rhythm.

• Sinus bradycardia

  A sinus rhythm slower than normal: every beat still starts in the sinus node, with a normal P wave and PR.

• Sinus tachycardia

  A sinus rhythm faster than 100/min.

Premature beats

• Sinus rhythm with premature ventricular complexes

  An early beat that starts in the ventricles instead of the sinus node.

Atrial and supraventricular

• Atrial fibrillation

  Disorganized atrial electrical activity with no effective atrial contraction.

• Atrial flutter

  A large re-entry circuit in the atria.

• Paroxysmal supraventricular tachycardia

  A regular narrow-complex tachycardia from a re-entry circuit that uses the AV node: inside the node (AV nodal re-entry, the most common type) or through an accessory pathway (AV re-entry).

AV blocks

• First-degree AV block

  Every atrial impulse reaches the ventricles, but late: the PR interval is longer than 200 ms and stays the same on every beat.

• Second-degree AV block, Mobitz I

  A second-degree AV block that is usually in the AV node: each impulse finds the node a little more tired, so conduction slows beat by beat until one P wave cannot pass.

• Second-degree AV block, Mobitz II

  Second-degree AV block in which the PR is constant on the conducted beats and a P wave suddenly fails to conduct.

• Second-degree AV block with 2:1 conduction

  Second-degree AV block in which every second P wave is not conducted: two P waves for each QRS, so the ventricular rate is half the atrial rate.

• Third-degree AV block with a junctional escape

  Complete (third-degree) AV block: no atrial impulse reaches the ventricles.

• Third-degree AV block with a ventricular escape

  Complete AV block with a ventricular escape rhythm: the block lies low in the conduction system, and a slow (usually 20–40/min), wide escape rhythm from the ventricles takes over.

• Atrial fibrillation with third-degree AV block

  Atrial fibrillation in which no fibrillatory impulse reaches the ventricles: a slow, regular escape rhythm (narrow if junctional, wide if ventricular) drives them instead.

Conduction, ST and QT

• Right bundle branch block

  The right bundle branch does not conduct, so the left ventricle activates first and the right ventricle late.

• Left bundle branch block

  The left bundle branch does not conduct, so activation spreads from the right ventricle across the septum to the left.

• Inferior ST elevation

  ST elevation in II, III and aVF from acute injury of the inferior wall, usually from occlusion of the right coronary artery (sometimes the circumflex), with reciprocal ST depression in aVL.

• Anterior ST elevation

  ST elevation in the anterior chest leads (V1–V4) from acute injury of the septum and anterior wall of the left ventricle, usually from occlusion of the left anterior descending (LAD) coronary artery.

• Prolonged QT interval

  Delayed ventricular repolarization: the QT interval, corrected for heart rate (QTc), is prolonged — 450 ms or more in men and 460 ms or more in women.

Ventricular and arrest rhythms

• Monomorphic ventricular tachycardia

  A regular wide-complex tachycardia arising in the ventricles: three or more ventricular beats in a row above 100/min (sustained if it lasts more than 30 seconds or needs termination because of instability).

• Torsades de pointes

  A polymorphic ventricular tachycardia that occurs with a long QT: the QRS complexes twist around the baseline as their axis and amplitude change.

• Ventricular fibrillation

  Chaotic, disorganized electrical activity of the ventricles with no effective contraction: there is no pulse and no cardiac output.

• Asystole

  No ventricular electrical activity: a flat line with no QRS complexes (when P waves continue without QRS complexes it is called ventricular standstill or P-wave asystole; this strip has none).

Pacing

• Ventricular pacing with loss of capture

  The pacemaker fires — a pacing spike appears — but the ventricle does not depolarize: some spikes are not followed by a paced QRS, and the heart depends on its own rhythm in those gaps.

Monitor pitfalls

• Sinus rhythm with artifact

  Signal on the ECG that does not come from the heart: patient movement, shivering or muscle tremor, poor electrode contact, or electrical interference.

Computed by the TracingsMD heart model (Junkers engine): simulated for education, not a patient recording and not for diagnosis.