Extra Resources

What does an electrocardiogram (ECG/EKG) measure?

An ECG measures the movement of electrical current through the heart during a heartbeat, which reflects the heart's electrical activity and conduction system.

What is depolarization?

Depolarization is the change in electrical charge distribution resulting in more positive ions, causing heart muscle contraction.

What is repolarization?

Repolarization is the return of ions to the resting state, resulting in relaxation of the heart muscle.

What is automaticity in cardiac cells?

Automaticity is the ability of cardiac cells to generate electrical impulses automatically without external stimulation.

Changes in automaticity can lead to arrhythmias.

What is re-entry in cardiac conduction?

Re-entry occurs when an electrical impulse follows a circular conduction pathway, repeatedly stimulating heart tissue and causing arrhythmias.

What is atrial kick?

Atrial kick is the additional blood pumped into the ventricles from atrial contraction, contributing about 30% of cardiac output.

Loss of atrial kick reduces cardiac output.

What is the normal electrical conduction pathway of the heart?

1⃣ SA node (pacemaker)
2⃣ Internodal pathways
3⃣ AV node (delays impulse)
4⃣ Bundle of His
5⃣ Right & Left bundle branches
6⃣ Purkinje fibers

What is the normal intrinsic rate of the SA node?

60–100 beats per minute

It is the primary pacemaker of the heart.

What does the P wave represent?

Atrial depolarization

Characteristics:

• precedes QRS complex

• normally upright, smooth, rounded

What does the PR interval represent?

The time from atrial depolarization to ventricular depolarization.

What does the QRS complex represent?

Ventricular depolarization

What does the ST segment represent?

The time between ventricular depolarization and repolarization.

Abnormalities:

• ST elevation → myocardial injury

• ST depression → ischemia

What does the T wave represent?

Ventricular repolarization

Normal shape:

• upright

• rounded

• smooth

What does the QT interval represent?

Time from start of ventricular depolarization to end of repolarization.

What does the U wave represent?

Not always visible.

Prominent U waves may indicate:

• hypokalemia

• hypercalcemia

• digoxin toxicity

How do you calculate heart rate using the 6-second rule?

1⃣ Count the number of QRS complexes in 6 seconds
2⃣ Multiply by 10

This gives the approximate heart rate per minute.

What are the 8 steps of ECG interpretation?

1⃣ Determine rhythm
2⃣ Determine heart rate
3⃣ Evaluate P waves
4⃣ Measure PR interval
5⃣ Evaluate QRS complex
6⃣ Evaluate T waves
7⃣ Measure QT interval
8⃣ Evaluate overall rhythm abnormalities

What are the characteristics of Normal Sinus Rhythm (NSR)?

• Rate 60–100 bpm

• Rhythm regular

• One P wave for every QRS

• P waves upright and rounded

• QRS complexes uniform

• Normal PR and QT intervals

• No ectopic beats

What is sinus bradycardia?

• Heart rate <60 bpm

• Rhythm regular

• All other ECG components normal

What are causes of sinus bradycardia?

• hyperkalemia

• hypothyroidism

• increased ICP

• sleep

• vomiting

• SA node disease

• inferior wall MI

• medications (beta blockers, digoxin)

How is symptomatic sinus bradycardia treated?

• Atropine

• Transcutaneous pacing

• Epinephrine infusion

• Dopamine infusion

What is sinus tachycardia?

• Heart rate >100 bpm

• Rhythm regular

• P waves may be hidden in T waves

Common causes of sinus tachycardia?

• fever

• pain

• anxiety

• hypovolemia

• heart failure

• pulmonary embolism

• stimulants (caffeine, nicotine)

What is atrial flutter?

• Atrial rate 250–350 bpm

• hallmark “flutter waves”

• QRS usually normal

• loss of atrial kick

Treatment for atrial flutter?

Unstable:

Immediate cardioversion

Stable:

• diltiazem

• verapamil

• digoxin

• amiodarone

What are ECG findings in atrial fibrillation?

• No P waves

• Irregularly irregular rhythm

• Chaotic fibrillatory waves

• Ventricular rate 100–150 bpm

What are common causes of atrial fibrillation?

• hypertension

• heart failure

• obesity

• sleep apnea

• pulmonary embolism

• electrolyte imbalance

• CAD

What is the treatment goal in atrial fibrillation?

Goal:

reduce ventricular rate to <80 bpm

Treatments:

• cardioversion (within 48 hrs)

• beta blockers

• calcium channel blockers

• anticoagulation therapy

What is a premature ventricular contraction (PVC)?

• early ventricular beat

• wide QRS complex

• no P wave

• pause after beat

Causes of PVCs?

• electrolyte imbalance

• hypoxia

• myocardial ischemia

• drug toxicity

• caffeine or alcohol

What is ventricular tachycardia?

• 3 or more PVCs in a row

• ventricular rate 100–250 bpm

• wide bizarre QRS

• life-threatening rhythm

Treatment for ventricular tachycardia?

Pulseless:

defibrillation + CPR

Pulse present:

• cardioversion

• amiodarone

What is ventricular fibrillation?

• chaotic electrical activity

• ventricles quiver

• no cardiac output

Treatment for ventricular fibrillation?

• Immediate defibrillation

• CPR

• epinephrine

• amiodarone

What is asystole?

• flatline ECG

• no electrical activity

• no pulse

• cardiac arrest

Treatment for asystole?

• confirm no pulse

• CPR immediately

• epinephrine

• treat underlying cause

What is third-degree AV block?

Complete heart block:

• P waves and QRS complexes independent

• atria and ventricles beat separately

Treatment for third-degree AV block?

• temporary pacing

• atropine

• dopamine or epinephrine

• permanent pacemaker often required

What is defibrillation?

A controlled electrical shock delivered randomly to restore rhythm in patients without a pulse.

What is cardioversion?

A synchronized electrical shock delivered during the QRS complex for patients with a pulse but unstable rhythm.

What is transcutaneous pacing?

Temporary pacing using external electrodes to stimulate heart contractions during severe bradycardia.

What is radiofrequency ablation?

A catheter procedure that destroys abnormal conduction pathways causing arrhythmias.