Arrhythmias & Conduction Blocks

Sinus Tachycardia

A fast heart rhythm (>100 bpm) originating from the sinoatrial (SA) node

Sinus Tachycardia (Origin)

Usually in response to physiological stress like fever, exercise, or anxiety.

Sinus Bradycardia

A slow heart rhythm (<60 bpm) from the SA node

Premature Atrial Contraction (PAC)

An early heartbeat originating in the atria; often benign and may feel like a "skipped beat."

Atrial Fibrillation (AFib)

An irregular and often rapid heart rhythm where multiple ectopic foci cause uncoordinated atrial activity

Atrial Fibrillation (Characterization)

Characterized by absence of P waves and irregularly irregular QRS complexes.

Atrial Flutter

A supraventricular rhythm with rapid and regular atrial contractions (around 300 bpm)

Atrial Flutter (Characterization)

Often producing a “sawtooth” pattern on ECG.

Paroxysmal Supraventricular Tachycardia (PSVT)

A sudden onset and termination of a rapid rhythm originating above the ventricles, typically due to a reentrant circuit.

AV Nodal Reentrant Tachycardia (AVNRT)

A common type of PSVT caused by a reentrant loop within the AV node.

AV Reentrant Tachycardia (AVRT)

A PSVT involving an accessory pathway allowing reentry outside the AV node.

Wolff-Parkinson-White (WPW) Syndrome

A pre-excitation syndrome where an accessory pathway causes a short PR interval and delta wave on ECG, predisposing to AVRT.

Multifocal Atrial Tachycardia (MAT)

A rhythm with multiple (≥3) different P-wave morphologies, often associated with pulmonary disease like COPD.

Premature Ventricular Contraction (PVC)

An early beat originating in the ventricles, presenting as a wide, abnormal QRS complex without a preceding P wave.

Ventricular Tachycardia (VT)

A fast, regular rhythm (usually >100 bpm) originating from the ventricles; may be monomorphic or polymorphic.

Monomorphic VT

A type of VT where all the QRS complexes look the same, indicating a single ectopic focus.

Polymorphic VT

A VT with varying QRS morphologies; suggests multiple foci or unstable ventricular tissue.

Torsades de Pointes

A specific type of polymorphic VT associated with a prolonged QT interval, where QRS complexes appear to twist around the baseline.

Ventricular Fibrillation (VFib)

A chaotic, disorganized electrical activity in the ventricles resulting in no effective cardiac output; a life-threatening emergency.

Junctional Escape Rhythm

A rhythm originating from the AV junction when the SA node fails; rate is 40–60 bpm with absent or retrograde P waves.

Accelerated Junctional Rhythm

A faster-than-normal junctional rhythm (60–100 bpm), often seen with digitalis toxicity or in cardiac surgery patients.

SA Exit Block

A conduction problem where impulses from the SA node are generated but do not exit to depolarize the atria; can cause missed beats.

First-Degree AV Block

A conduction delay at the AV node causing a consistently prolonged PR interval (>200 ms), but all atrial impulses are conducted to the ventricles.

Second-Degree AV Block

Some atrial impulses fail to conduct to the ventricles; two subtypes

Mobitz Type I (Second-Degree AV Block)

Progressive prolongation of the PR interval until a QRS complex is dropped.

Mobitz Type II (Second-Degree AV Block)

Intermittent failure of conduction without PR prolongation; usually due to block below the AV node and often more serious.

Third-Degree (Complete) AV Block

Complete dissociation between atrial and ventricular activity; no atrial impulses are conducted, and the ventricles beat independently via an escape rhythm.

Right Bundle Branch Block (RBBB)

A block in the _____ bundle of His, leading to delayed right ventricular depolarization; characterized by a widened QRS and RSR' pattern in lead V1.

Left Bundle Branch Block (LBBB)

A block in the ____ bundle branch, causing delayed left ventricular activation; presents as a wide QRS complex and broad/notched R waves in lateral leads (I, V5–V6).