ECG basics

What does ECG stand for?

Electrocardiogram

What is the primary purpose of an ECG?

To record the electrical activity of the heart and detect abnormalities in rhythm, rate, or conduction.

How many leads are typically used in a standard 12-lead ECG?

10 leads (6 precordial leads + 4 limb leads).

What is the P wave?

Represents atrial depolarization.

What does the QRS complex represent?

Ventricular depolarization.

What does the T wave represent?

Ventricular repolarization.

What is the PR interval?

The time from the start of atrial depolarization to the start of ventricular depolarization (normal: 0.12–0.20 seconds).

What is the QT interval?

The time from the start of ventricular depolarization to the end of ventricular repolarization (varies with heart rate).

What is the ST segment?

The flat section of the ECG between the end of the S wave and the start of the T wave; represents the period between ventricular depolarization and repolarization.

What is a normal PR segment?

The PR segment (from the end of the P wave to the start of the QRS complex) is normally isoelectric (flat).

What is the normal heart rate range?

60–100 beats per minute.

What defines normal sinus rhythm?

• Regular rhythm.

• Heart rate 60–100 bpm.

• P waves present before every QRS complex.

• PR interval 0.12–0.20 seconds.

What is the sinus node?

The heart’s natural pacemaker, located in the right atrium, responsible for initiating the heartbeat.

What is sinus arrhythmia?

A normal variation in heart rate where the rhythm speeds up during inspiration and slows down during expiration.

How does sinus bradycardia differ from normal sinus rhythm?

Heart rate <60 bpm but otherwise normal.

How does sinus tachycardia differ from normal sinus rhythm?

Heart rate >100 bpm but otherwise normal.

What causes sinus arrhythmia?

Changes in vagal tone during breathing (common in young, healthy individuals).

Is sinus arrhythmia usually pathological?

No, it is typically benign.

What is sinus pause?

A temporary absence of sinus node activity, resulting in a pause in the ECG rhythm.

What is sick sinus syndrome?

A group of arrhythmias caused by dysfunction of the sinus node, often leading to bradycardia or alternating bradycardia and tachycardia.

What is chronotropic incompetence?

The inability of the heart to increase its rate appropriately in response to exercise or stress.

What is atrial fibrillation (AFib)?

A chaotic, irregular atrial rhythm with no discernible P waves and an irregularly irregular ventricular response.

What are the two types of atrial flutter?

1. Typical atrial flutter (counterclockwise re-entry).

2. Atypical atrial flutter (other re-entry circuits).

What is the atrial rate in atrial flutter?

250–350 bpm.

What is atrial tachycardia?

A rapid rhythm originating from an ectopic focus in the atria (>100 bpm).

What is multifocal atrial tachycardia (MAT)?

A rhythm with ≥3 different P wave morphologies and a rate >100 bpm, often seen in COPD or electrolyte imbalances.

What is wandering atrial pacemaker?

A rhythm where the pacemaker site shifts between the SA node, atria, and AV node, resulting in ≥3 different P wave morphologies and a rate <100 bpm.

What is premature atrial contraction (PAC)?

An early beat originating from an ectopic focus in the atria, causing a premature P wave.

What is ectopic atrial rhythm?

A rhythm where the pacemaker is outside the SA node, resulting in abnormal P waves.

What is supraventricular tachycardia (SVT)?

A rapid rhythm (>100 bpm) originating above the ventricles, often due to re-entry circuits (e.g., AVNRT, AVRT).

What is AV nodal reentrant tachycardia (AVNRT)?

A type of SVT caused by a re-entry circuit within the AV node.

What is a junctional rhythm?

A rhythm originating from the AV junction (AV node or His bundle), with absent or inverted P waves before or after the QRS.

What is the junctional escape rhythm?

A rhythm that occurs when the SA node fails, and the AV junction takes over as the pacemaker (rate: 40–60 bpm).

What is accelerated junctional rhythm?

A junctional rhythm with a rate 60–100 bpm.

What is junctional tachycardia?

A junctional rhythm with a rate >100 bpm.

What is premature junctional contraction (PJC)?

An early beat originating from the AV junction, causing a premature QRS complex.

What is ventricular tachycardia (VT)?

A rapid rhythm (>100 bpm) originating from the ventricles, characterized by wide QRS complexes and no P waves.

What is ventricular fibrillation (VFib)?

A chaotic, irregular rhythm with no discernible QRS complexes, leading to cardiac arrest.

What is idioventricular rhythm?

A slow ventricular rhythm (20–40 bpm) that occurs when the SA and AV nodes fail. Often seen during reperfusion after a heart attack.

What is accelerated idioventricular rhythm (AIVR)?

A ventricular rhythm with a rate 40–100 bpm. Often benign and seen during reperfusion (e.g., after thrombolytics or PCI).

What is premature ventricular contraction (PVC)?

An early beat originating from an ectopic focus in the ventricles, causing a premature, wide QRS complex. Can be unifocal (same morphology) or multifocal (different morphologies).

What is torsades de pointes?

A polymorphic ventricular tachycardia associated with a prolonged QT interval.

What is ventricular escape rhythm?

A rhythm that occurs when higher pacemakers fail, and the ventricles take over (rate: 20–40 bpm). No P waves and wide QRS complexes.

What is asystole?

The absence of electrical activity in the heart (flatline). Requires CPR and epinephrine.

What is pulseless electrical activity (PEA)?

A condition where electrical activity is present on the ECG but there is no mechanical contraction (no pulse). Causes: hypovolemia, tamponade, tension pneumothorax, massive PE.

What is agonal rhythm?

A dying heart rhythm characterized by slow, irregular, wide QRS complexes before asystole.

What is a first-degree AV block?

A delay in conduction through the AV node, resulting in a prolonged PR interval (>0.20 seconds).

What is a second-degree AV block Type I (Wenckebach)?

A progressive lengthening of the PR interval until a QRS complex is dropped.

What is a second-degree AV block Type II?

Intermittent non-conducted P waves without progressive PR interval lengthening (more serious than Type I).

What is a third-degree AV block (complete heart block)?

No conduction from the atria to the ventricles; atria and ventricles beat independently.

What is bundle branch block (BBB)?

A delay or block in one of the bundle branches, resulting in a wide QRS complex (>0.12 seconds).

What is right bundle branch block (RBBB)?

A block in the right bundle branch, causing a rabbit-ear appearance in V1–V3.

What is left bundle branch block (LBBB)?

A block in the left bundle branch, causing a wide QRS with a broad, notched R wave in V5–V6.

What is hemiblock?

A block in one of the fascicles of the left bundle branch (anterior or posterior).

What is bifascicular block?

A combination of RBBB + left anterior hemiblock or RBBB + left posterior hemiblock.

What is trifascicular block?

A combination of RBBB + LAFB + first-degree AV block or RBBB + LPFB + first-degree AV block.

What is a single-chamber pacemaker?

A pacemaker that paces either the atrium or ventricle (not both).

What is a dual-chamber pacemaker?

A pacemaker that paces both the atrium and ventricle, mimicking normal cardiac physiology.

What is pacemaker syndrome?

A condition where the timing of atrial and ventricular contractions is not synchronized, leading to symptoms like fatigue or dizziness.

What is failure to capture?

A pacemaker malfunction where the electrical impulse does not cause myocardial depolarization.

What is failure to sense?

A pacemaker malfunction where the pacemaker does not detect the patient’s intrinsic rhythm and fires inappropriately.

What is the most common cause of sudden cardiac death?

Ventricular fibrillation (VFib).

What is the treatment for stable VT with a pulse?

Amiodarone, Lidocaine, Procainamide

What is the treatment for pulseless VT/VFib?

CPR + defibrillation (immediate unsynchronized shock), Epinephrine, Amiodarone

What is the treatment for unstable VT with a pulse?

Synchronized cardioversion.

What is the treatment for torsades de pointes?

Magnesium sulfate, correct electrolytes, and possibly overdrive pacing. Avoid drugs that prolong QT.

What is the treatment for complete heart block?

Pacemaker insertion.

What is the treatment for asystole?

CPR + epinephrine, but defibrillation is not indicated.

What is the treatment for atrial fibrillation with rapid ventricular response?

• Rate control (beta-blockers, calcium channel blockers).

• Rhythm control (amiodarone, cardioversion).

• Anticoagulation (if >48 hours).

What is the treatment for Wolff-Parkinson-White (WPW) syndrome?

Avoid AV nodal blockers (e.g., adenosine, beta-blockers); use procainamide or amiodarone or radiofrequency ablation.

What is the treatment for idioventricular rhythm?

• No treatment needed if asymptomatic.

• If symptomatic (hypotension, chest pain):

  • Atropine (0.5–1 mg IV).

  • Dopamine or epinephrine (for hypotension).

  • Pacemaker (if refractory).

What is the treatment for PVCs?

• No treatment needed if asymptomatic.

• If symptomatic or high risk:

  • Beta-blockers (first-line).

  • Amiodarone or lidocaine (for frequent PVCs).

  • Correct electrolytes (K+, Mg).

What is the treatment for bradycardia with symptoms?

Atropine or transcutaneous pacing.

What does ST elevation indicate?

Acute myocardial infarction (STEMI) or pericarditis.

What does ST depression indicate?

Myocardial ischemia, subendocardial infarction, or digoxin effect

What does Q waves indicate?

Old myocardial infarction (unless in aVR or III).

What does inverted T waves indicate?

Myocardial ischemia, CNS events, or electrolyte imbalances.

What does low voltage QRS indicate?

Hypothyroidism, COPD, pericardial effusion, or obesity

What does right axis deviation indicate?

Right ventricular hypertrophy, COPD, or pulmonary embolism.

What does left axis deviation indicate?

Left anterior hemiblock, inferior MI, or LVH.

What does brugada pattern indicate?

Brugada syndrome, a genetic disorder predisposing to ventricular arrhythmias.

What is the difference between a rhythm strip and a 12-lead ECG?

• Rhythm strip: Single lead (e.g., lead II) for continuous monitoring.

• 12-lead ECG: 12 different views of the heart for diagnostic purposes.

What is the normal QRS duration?

<0.12 seconds.

What is the normal QT interval?

<0.44 seconds (varies with heart rate).

What is electrical alternans?

Alternating amplitude of QRS complexes, seen in pericardial effusion or cardiac tamponade.

What is R-on-T phenomenon?

A PVC occurring on the T wave of the preceding beat, which can trigger ventricular tachycardia.

What is concordance in ECG?

All precordial leads (V1–V6) show the same polarity (either all positive or all negative), suggesting VT.

What is concordance sign?

A sign of ventricular tachycardia where the QRS complexes in V1–V6 all point in the same direction.

What is fusion beat?

A hybrid beat where a PVC and a sinus beat merge, seen in VT (not SVT with aberrancy).

What is capture beat?

A normal QRS complex that occurs during VT due to the sinus node briefly capturing the ventricles. Confirms VT.

What is digoxin effect?

Scooped ST segments and shortened QT interval, seen with digoxin therapy.

What is Osborn wave (J wave)?

A positive deflection at the end of the QRS, seen in hypothermia.

What is early repolarization?

Concave ST elevation with notched J point, commonly seen in young, healthy individuals.

What is pericarditis?

Diffuse ST elevation with PR depression, often in multiple leads.

What is hyperkalemia?

Peaked T waves, widened QRS, and sine wave pattern in severe cases.

What is hypokalemia?

Flat T waves, U waves, and ST depression.

What is hypercalcemia?

Shortened QT interval.

What is hypocalcemia?

Prolonged QT interval.

What is Lown-Ganong-Levine (LGL) syndrome?

A short PR interval with a normal QRS, due to an accessory pathway (James bundle).

What is Wolff-Parkinson-White (WPW) syndrome?

A short PR interval, delta wave, and wide QRS due to an accessory pathway (Bundle of Kent).