The ECG Flashcards
(20 cards)
What is an ECG?
An electrocardiogram (ECG or EKG) is a recording of the electrical activity of the heart over time, captured through surface electrodes placed on the skin.
What does the P wave represent?
Atrial depolarization, initiated by the SA node.
What does the PR interval represent?
Time from onset of atrial depolarization to the onset of ventricular depolarization; includes the AV node delay.
Normal range: 0.12–0.20 seconds.
What does the QRS complex represent?
Ventricular depolarization.
Normal duration: < 0.12 seconds.
What does the T wave represent?
Ventricular repolarization.
What is the ST segment, and what is its clinical importance?
The ST segment represents the period between ventricular depolarization and repolarization.
• Elevation or depression may indicate myocardial ischemia or infarction
What is the QT interval?
The time from the start of ventricular depolarization to the end of ventricular repolarization.
• Prolongation can predispose to arrhythmias like Torsades de Pointes.
How do you calculate heart rate from an ECG?
•Count the number of large squares between two R waves, then use:
Heart rate = 300 / number of large squares between R waves
•OR count small squares and divide 1500 by the number of small squares.
What is a normal sinus rhythm?
• P wave before every QRS
• Regular rhythm
• Rate: 60–100 bpm
• Originates from the SA node
What does atrial fibrillation look like on ECG?
• Irregularly irregular rhythm
• No discrete P waves
• Variable R-R intervals
What does atrial flutter look like?
• “Sawtooth” flutter waves
• Regular atrial activity (~300 bpm)
• Ventricular response may be regular or irregular
What does ventricular tachycardia look like?
• Broad QRS complexes
• Rapid, regular rhythm
• No visible P waves
• May progress to ventricular fibrillation
What is seen in ventricular fibrillation?
•Chaotic, irregular waveform
• No identifiable P waves, QRS complexes, or T waves
• Medical emergency
What is a first-degree AV block?
•Prolonged PR interval (>0.20 sec)
• Every P wave followed by a QRS
What characterizes a second-degree AV block – Mobitz Type I (Wenckebach)?
• Progressively lengthening PR interval
• Eventually a dropped QRS complex
What characterizes a second-degree AV block – Mobitz Type II?
• Constant PR interval with intermittently dropped QRS
• More dangerous, can progress to complete block
What is a third-degree (complete) AV block?
• No association between P waves and QRS complexes
• Atria and ventricles beat independently
What does left axis deviation (LAD) suggest?
Can indicate left ventricular hypertrophy, left anterior fascicular block, or inferior MI.
What does right axis deviation (RAD) suggest?
Seen in right ventricular hypertrophy, pulmonary embolism, or lateral MI
What are classic ECG findings in myocardial infarction?
• ST elevation in leads overlying the infarct area
• Pathologic Q waves
• T wave inversions post-MI
