EKG Waveform Lesson

This page introduces the various components of an EKG waveform.

EKG Waveform

ekg waveform component names

Letters are used to indicate important points on a typical waveform.

PR Interval

ekg waveform component names

The PR Interval indicates atrioventricular conduction time. The interval is measured from where the P wave begins until the beginning of the QRS complex.

QRS Complex

ekg qrs complex

The QRS complex indicates ventricular depolarization. The QRS interval is measured from the end of the PR interval to the end of the S wave.

QT Interval

ekg qt interval

The QT interval indicates ventricular activity, both depolarization and repolarization. Measure the QT interval from the beginning of the QRS complex to the end of the T wave.

ST Interval

ekg st segment

The ST segment traces the early part of ventricular repolarization. The ST segment begins at the end of the QRS complex and continues to beginning of the T wave.

How To Read An EKG - Lectures

Use EKG.Academy's library of free presentations on cardiac rhythms. These training materials present the fundamentals for each major category of cardiac rhythms. The fundamentals are reinforced with practice exercises throughout each lecture.

EKG Lectures

Abnormal EKG Types

A summary of each of the most common EKG types is provided below.

Accelerated Idioventricular Rhythm
EKG Tracing
EKG rhythm is regular with heart rate that is 50-120 bpm. The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (>0.10 sec), bizarre looking. .
Accelerated Junctional Rhythm
EKG Tracing
EKG rhythm is regular with heart rate that is normal (60-100 bpm). The P wave features: present before, during (hidden) or after qrs, if visible it is inverted. Notice that the PR interval is not measurable. The QRS complex will usually be normal (0.06-0.10 sec). .
Asystole
EKG Tracing
EKG rhythm is not present with heart rate that is absent. The P wave features: absent. Notice that the PR interval is absent. The QRS complex will usually be absent. confirm with multiple leads.
Atrial Fibrillation
EKG Tracing
EKG rhythm is irregular with heart rate that is very fast (> 350 bpm) for atrial, but ventricular rate may be slow, normal or fast. The P wave features: absent - erratic waves are present. Notice that the PR interval is absent. The QRS complex will usually be normal but may be widened if there are conduction delays. .
Atrial Flutter
EKG Tracing
EKG rhythm is regular or irregular with heart rate that is fast (250-350 bpm) for atrial, but ventricular rate is often slower. The P wave features: not observable, but saw-toothed flutter waves are present. Notice that the PR interval is not measureable. The QRS complex will usually be normal (0.06-0.10 sec). .
Bundle Branch Block
EKG Tracing
EKG rhythm is regular with heart rate that is the underlying rate. The P wave features: normal. Notice that the PR interval is normal (0.12-0.20 sec). The QRS complex will usually be wide (>0.12 sec). .
First Degree Heart Block
EKG Tracing
EKG rhythm is regular with heart rate that is the underlying rate. The P wave features: normal. Notice that the PR interval is prolonged (>0.20 sec). The QRS complex will usually be normal (0.06-0.10 sec). a first degree av block occurs when electrical impulses moving through the atrioventricular (av) node are delayed (but not blocked). first degree indicates slowed conduction without missed beats..
Idioventricular Rhythm
EKG Tracing
EKG rhythm is regular with heart rate that is slow (20-40 bpm). The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (>0.10 sec), bizarre appearance. .
Junctional Escape Rhythm
EKG Tracing
EKG rhythm is regular with heart rate that is slow (40-60 bpm). The P wave features: present before, during (hidden) or after qrs, if visible it is inverted. Notice that the PR interval is not measurable. The QRS complex will usually be normal (0.06-0.10 sec). .
Junctional Tachycardia
EKG Tracing
EKG rhythm is regular with heart rate that is fast (100-180 bpm). The P wave features: present before, during (hidden) or after qrs, if visible it is inverted. Notice that the PR interval is absent or short. The QRS complex will usually be normal (0.06-0.10 sec). .
Multifocal Atrial Tachycardia
EKG Tracing
EKG rhythm is irregular with heart rate that is fast (> 100 bpm). The P wave features: often changing shape and size from beat to beat (at least three differing forms). Notice that the PR interval is variable. The QRS complex will usually be normal (0.06-0.10 sec). t wave is often distorted also review wandering atrial pacemaker lesson.
Normal Sinus Rhythm
EKG Tracing
EKG rhythm is regular with heart rate that is normal (60-100 bpm). The P wave features: normal (positive & precedes each qrs). Notice that the PR interval is normal (0.12-0.20 sec). The QRS complex will usually be normal (0.06-0.10 sec). .
Pacemaker Failure to Capture
EKG Tracing
EKG rhythm is irregular with heart rate that is slow or normal. The P wave features: . Notice that the PR interval is . The QRS complex will usually be . pacemaker spikes are not followed by p waves or qrs complexes.
Pacemaker Failure to Pace
EKG Tracing
EKG rhythm is irregular with heart rate that is . The P wave features: . Notice that the PR interval is . The QRS complex will usually be . pacemaker spikes do not appear.
Pacemaker Single Chamber Atrial
EKG Tracing
EKG rhythm is regular with heart rate that is 60 bpm. The P wave features: normal. Notice that the PR interval is normal. The QRS complex will usually be normal. .
Premature Atrial Complex
EKG Tracing
EKG rhythm is irregular with heart rate that is usually normal but depends on underlying rhythm. The P wave features: premature, positive and shape is abnormal. Notice that the PR interval is normal or longer. The QRS complex will usually be 0.10 sec or less. .
Premature Junctional Complex
EKG Tracing
EKG rhythm is regular with premature beats with heart rate that is the underlying rate. The P wave features: present before, during (hidden) or after qrs, if visible it is inverted. Notice that the PR interval is absent or short. The QRS complex will usually be normal (0.06-0.10 sec). .
Premature Ventricular Complex
EKG Tracing
EKG rhythm is irregular with heart rate that is the underlying rate. The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (> 0.10 sec), bizarre appearance. two pvcs together are termed a couplet while three pvcs in a row with a fast rhythm is ventricular tachycardia.
Premature Ventricular Complex Bigeminy
EKG Tracing
EKG rhythm is irregular with heart rate that is the underlying rate. The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (> 0.10 sec), bizarre appearance. pvc appears every second beat.
Premature Ventricular Complex Quadrigeminy
EKG Tracing
EKG rhythm is irregular with heart rate that is the underlying rate. The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (> 0.10 sec), bizarre appearance. pvc appears every fourth beat.
Premature Ventricular Complex Trigeminy
EKG Tracing
EKG rhythm is irregular with heart rate that is the underlying rate. The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (> 0.10 sec), bizarre appearance. pvc appears every third beat.
Second Degree Heart Block Type I
EKG Tracing
EKG rhythm is irregular but with progressively longer pr interval lengthening with heart rate that is the underlying rate. The P wave features: normal. Notice that the PR interval is progressively longer until a qrs complex is missed, then cycle repeats. The QRS complex will usually be normal (0.06-0.10 sec). .
Second Degree Heart Block Type II
EKG Tracing
EKG rhythm is regular (atrial) and irregular (ventricular) with heart rate that is characterized by atrial rate usually faster than ventricular rate (usually slow). The P wave features: normal form, but more p waves than qrs complexes. Notice that the PR interval is normal or prolonged. The QRS complex will usually be normal or wide. .
Sinoatrial Block
EKG Tracing
EKG rhythm is irregular when sa block occurs with heart rate that is normal or slow. The P wave features: normal. Notice that the PR interval is normal (0.12-0.20 sec). The QRS complex will usually be normal (0.06-0.10 sec). pause time is an integer multiple of the p-p interval try to identify specific type of atrial tachycardia - see other pages.
Sinus Arrest
EKG Tracing
EKG rhythm is irregular due to pause with heart rate that is normal to slow. The P wave features: normal. Notice that the PR interval is normal (0.12-0.20 sec). The QRS complex will usually be normal (0.06-0.10 sec). pause time is not an integer multiple of the p-p interval.
Sinus Arrhythmia
EKG Tracing
EKG rhythm is irregular, varying with respiration with heart rate that is normal (60-100 bpm) and rate may increase during inspiration. The P wave features: normal. Notice that the PR interval is normal (0.12-0.20 sec). The QRS complex will usually be normal (0.06-0.10 sec). heart rate frequently increases with inspiration, decreasing with expiration.
Sinus Bradycardia
EKG Tracing
EKG rhythm is regular with heart rate that is slow (< 60 bpm). The P wave features: normal. Notice that the PR interval is normal (0.12-0.20 sec). The QRS complex will usually be normal (0.06-0.10 sec). .
Sinus Tachycardia
EKG Tracing
EKG rhythm is regular with heart rate that is fast (> 100 bpm). The P wave features: normal, may merge with t wave at very fast rates. Notice that the PR interval is normal (0.12-0.20 sec). The QRS complex will usually be normal (0.06-0.10 sec). qt interval shortens with increasing heart rate.
Supraventricular Tachycardia
EKG Tracing
EKG rhythm is regular with heart rate that is fast (150-250 bpm). The P wave features: merged with t wave. Notice that the PR interval is normal (0.12 sec). The QRS complex will usually be normal (.10 sec). pr interval can be difficult to measure.
Third Degree Heart Block
EKG Tracing
EKG rhythm is regular, but atrial and ventricular rhythms are independent with heart rate that is characterized by atrial rate usually normal and faster than ventricular rate. The P wave features: normal shape and size, may appear within qrs complexes. Notice that the PR interval is absent: the atria and ventricles beat independently.. The QRS complex will usually be normal, but wide if junctional escape focus. .
Ventricular Fibrillation
EKG Tracing
EKG rhythm is highly irregular with heart rate that is unmeasurable. The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be none. ekg tracings is a wavy line.
Ventricular Tachycardia
EKG Tracing
EKG rhythm is regular with heart rate that is fast (100-250 bpm). The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (>0.10 sec), bizarre appearance. .
Ventricular Tachycardia Monomorphic
EKG Tracing
EKG rhythm is regular with heart rate that is fast (100-250 bpm). The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (>0.10 sec), bizarre looking. .
Ventricular Tachycardia Polymorphic
EKG Tracing
EKG rhythm is regular or irregular with heart rate that is fast (100-300 bpm). The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be normal or wide (>0.10 sec), bizarre looking. .
Ventricular Tachycardia Torsade de Pointes
EKG Tracing
EKG rhythm is irregular with heart rate that is fast (200-250 bpm). The P wave features: absent. Notice that the PR interval is not measurable. The QRS complex will usually be wide (>0.10 sec), bizarre looking. .
Wandering Atrial Pacemaker
EKG Tracing
EKG rhythm is may be irregular with heart rate that is normal (60-100 bpm). The P wave features: changing shape and size from beat to beat (at least three diffferent forms). Notice that the PR interval is variable. The QRS complex will usually be normal (0.06-0.10 sec). t wave normal. if heart rate exceeds 100 bpm, then rhythm may be multifocal atrial tachycardia (map).
Wolff-Parkinson-White Syndrome
EKG Tracing
EKG rhythm is regular unless atrial fibrillation present with heart rate that is normal (60-100 bpm). The P wave features: normal. Notice that the PR interval is can be short (<0.12 sec). The QRS complex will usually be usually wide (> 0.12 sec). look for short pr interval and/or delta wave a delta wave (positive or negative) distorts the early part of the qrs complex.

ECG interpretation help and practice strips can be found at thePracticalClincicalSkills.com ECG interpretation page.

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Spanish Edition

In cooperation with Project Semilla, we have recently launched Spanish Editions of several of our ECG training modules.

Guía de referencia de los ritmos cardíacos
Paciente Virtual Prueba con Monitor
Ejercicios de práctica de ritmos cardíacos
Conceptos Básicos ECG