Rhythm and triggers of arrhythmia

What is the standard ECG paper speed?

25 mm per second

What vertical calibration is used in standard ECG recording?

1 mV produces a 1 cm vertical deflection

How long does one small ECG square represent?

0.04 seconds

How long does one large ECG square represent?

0.2 seconds

How many large squares equal one second on ECG paper?

5 large squares

How many large squares equal one minute on ECG paper?

300 large squares

How many small squares equal one minute on ECG paper?

1500 small squares

Formula to calculate heart rate using small squares?

Heart rate = 1500 ÷ number of small squares between consecutive R waves

Formula to calculate heart rate using large squares?

Heart rate = 300 ÷ number of large squares between consecutive R waves

What ECG feature is used to calculate heart rate?

R–R interval

First step in rhythm analysis?

Determine regularity

Second step in rhythm analysis?

Calculate heart rate

Third step in rhythm analysis?

Assess P waves

Fourth step in rhythm analysis?

Determine PR interval

Fifth step in rhythm analysis?

Determine QRS duration

How do you assess ECG regularity?

Compare R–R intervals for equal spacing

Define regular rhythm on ECG

R–R intervals are equidistant

Define regularly irregular rhythm

Irregular pattern that repeats predictably

Define irregularly irregular rhythm

Completely unpredictable R–R intervals

Key ECG feature to examine for atrial activity

P waves

What questions should be asked when assessing P waves?

Are P waves present, identical, regular, and preceding every QRS

What does one P wave before every QRS indicate?

Sinus origin of rhythm

Normal PR interval range

0.12–0.20 seconds

Normal PR interval in ECG boxes

3–5 small boxes

What does the PR interval represent?

Time from atrial depolarization to ventricular depolarization

Normal QRS duration range

0.04–0.12 seconds

Normal QRS duration in ECG boxes

1–3 small boxes

What does a narrow QRS complex indicate?

Supraventricular origin of ventricular activation

What is considered a narrow QRS duration?

Less than 0.12 seconds

What ECG features define normal sinus rhythm?

Regular rhythm, rate 60–100 bpm, normal P waves, PR 0.12–0.20 s, QRS <0.12 s

Heart rate range for normal sinus rhythm

60–100 bpm

ECG origin of sinus rhythm

Sinoatrial node

Define sinus bradycardia

Sinus rhythm with heart rate less than 60 bpm

Common causes of sinus bradycardia

Athletes, sleep, increased vagal tone

ECG features of sinus bradycardia

Regular rhythm, normal P waves, PR normal, slow rate

Define sinus tachycardia

Sinus rhythm with heart rate greater than 100 bpm

Typical heart rate in sinus tachycardia

Usually 100–150 bpm

ECG features of sinus tachycardia

Regular rhythm, normal P waves, gradual onset and offset

Physiologic causes of sinus tachycardia

Exercise, fever, anxiety, anemia

Define sinus arrhythmia

Irregular sinus rhythm with respiratory variation

Key feature that distinguishes sinus arrhythmia from atrial fibrillation

P waves are present before every QRS

Define atrial fibrillation

Irregularly irregular rhythm with no visible P waves

Key ECG hallmark of atrial fibrillation

Absent P waves and chaotic baseline

QRS width in atrial fibrillation

Narrow QRS

Clinical risk associated with atrial fibrillation

Increased risk of stroke

Define atrial flutter

Organized atrial reentry rhythm

Characteristic ECG appearance of atrial flutter

Sawtooth flutter waves

Best ECG leads to see atrial flutter waves

Leads II, III, and aVF

Typical atrial rate in atrial flutter

Approximately 300 bpm

Common ventricular rate in atrial flutter

Approximately 150 bpm due to 2:1 block

Define supraventricular tachycardia (SVT)

Regular narrow-complex tachycardia originating above the ventricles

Typical heart rate range in SVT

150–250 bpm

Visibility of P waves in SVT

P waves often not visible

Most common mechanisms of SVT

AV nodal reentrant tachycardia or atrioventricular reentrant tachycardia

Define ventricular tachycardia

Wide-complex regular tachycardia originating from ventricles

Key ECG feature distinguishing ventricular tachycardia

Wide QRS complexes

Clinical importance of ventricular tachycardia

Life-threatening, assume VT until proven otherwise

Define ventricular fibrillation

Chaotic, disorganized ventricular rhythm with no cardiac output

ECG appearance of ventricular fibrillation

No identifiable P waves, QRS complexes, or T waves

Immediate treatment for ventricular fibrillation

Immediate defibrillation

Define junctional rhythm

Rhythm originating from the atrioventricular junction

Typical heart rate of junctional rhythm

40–60 bpm

P wave appearance in junctional rhythm

P waves absent or inverted

QRS width in junctional rhythm

Narrow QRS

Cause of junctional rhythm

Sinoatrial node failure or atrioventricular node takeover

Define first-degree atrioventricular block

Prolonged PR interval with all P waves conducting

PR interval criterion for first-degree AV block

Greater than 200 milliseconds

Dropped beats in first-degree AV block

None

Clinical significance of first-degree AV block

Usually benign

Define second-degree atrioventricular block

Some P waves do not conduct to QRS complexes

Key ECG feature of second-degree AV block

Intermittent dropped QRS complexes

Types of second-degree AV block

Mobitz type I and Mobitz type II

Define Mobitz type I (Wenckebach) AV block

Progressively lengthening PR interval followed by dropped QRS

ECG pattern in Mobitz type I

Grouped beating

Location of problem in Mobitz type I

Atrioventricular node

Clinical significance of Mobitz type I

Often benign

Define third-degree atrioventricular block

Complete atrioventricular dissociation

Relationship between P waves and QRS in third-degree block

No relationship

Type of rhythm maintaining ventricles in third-degree block

Ventricular escape rhythm

Management of third-degree AV block

Pacemaker usually required

One-line ECG clue for atrial fibrillation

Irregularly irregular rhythm with no P waves

One-line ECG clue for atrial flutter

Sawtooth waves with ventricular rate around 150 bpm

One-line ECG clue for SVT

Regular narrow tachycardia with absent P waves

One-line ECG clue for ventricular tachycardia

Wide-complex tachycardia