ECG CHANGES THEORETICAL PRACTICE

• P wave: Sawtooth flutter waves (F waves)

• QRS: Normal/narrow

• PR Interval: Not measurable

• Rhythm: Regular or irregular

• Notes: Atrial rate ~250–350 bpm, not every F wave leads to a QRS

Atrial Flutter

• P wave: Absent/Abnormal, replaced by fibrillatory waves (F Waves)

• QRS: Normal/narrow

• PR Interval: Not measurable

• Rhythm: Irregularly irregular

• Notes: No organized atrial activity, high risk of clot

Atrial Fibrillation

• P wave: Tall P Wave, may be buried in QRS or retrograde

• QRS: Narrow

• PR Interval: Not visible or short

• Rhythm: Regular, very fast (150–250 bpm)

• Notes: Sudden onset and offset, re-entry circuit above ventricles

Supraventricular Tachycardia

• P wave: Absent

• QRS: Wide and bizarre (>0.12s)

• PR Interval: Not measurable

• Rhythm: Regular (monomorphic) or slightly irregular (polymorphic)

• Notes: Can be with or without pulse; emergency

Ventricular Tachycardia

• P wave: Absent

• QRS: Absent, replaced by chaotic waves

• PR Interval: Not measurable

• Rhythm: Totally disorganized

• Notes: No cardiac output; requires immediate defibrillation

Ventricular Fibrillation

• P wave: Present, 1:1 with QRS

• QRS: Normal

• PR Interval: Prolonged (>0.20s), constant

• Rhythm: Regular

• Notes: Benign, just delayed conduction through AV node

1st Degree AV Block

• P wave: Present

• QRS: Normal then Dropped

• PR Interval: Progressively lengthens until QRS is dropped

• Rhythm: Irregular

2nd Degree AV Block: Wenckebach or Mobitz Type I

• P wave: Present

• QRS: Normal then Dropped

• PR Interval: Constant when present

• Rhythm: Irregular

• Notes: More dangerous than Type I, risk of progressing to 3rd-degree

2nd Degree AV Block: Mobitz Type II

• P wave: Present, but no relation to QRS

• QRS: Normal or widened

• PR Interval: Variable

• Rhythm: Regular atrial, regular ventricular, but independent of each other

• Notes: No signal from atria to ventricles — complete dissociation

3rd Degree AV Block

• P wave: Early, abnormal shape

• QRS: Normal

• PR Interval: Usually normal or shortened

• Rhythm: Irregular (due to early beat)

• Notes: Usually followed by a brief pause; benign

Premature Atrial Contraction

• P wave: Absent (originates in ventricles)

• QRS: Wide, bizarre

• PR Interval: Not measurable

• Rhythm: Irregular (due to premature beat)

• Notes: Often followed by a compensatory pause; may be unifocal or multifocal

Premature Ventricular Contraction