1. Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program7
QRS Complexes
Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program

2. QRS Complexes
Examining the QRS complexes is another initial step of analyzing the ECG
Question to ask: “What are the first, second and third steps used to analyze the ECG tracing?”
Answer: Checking the heart rate, regularity and assessing the P waves.
Instructional point:
The QRS complex follows the PR interval. Q I

3. Assessing the QRS Complexes
Yields important information
Tells us how well the impulses are traveling through the ventricles or if the impulses are originating from the ventricles
delays or interruption of conduction through the ventricles or impulses that arise from the ventricles can lead to serious or even life-threatening conditions

4. QRS Complex
QRS complex is the waveform immediately following the PR interval
Consists of
Q wave
first negative deflection from the baseline following the P wave
R wave
first positive deflection following the Q wave
S wave
first negative deflection that extends below the baseline following the R wave
Instructional point:
The QRS complex is larger than the P wave because ventricular depolarization involves a considerably larger muscle mass than atrial depolarization and because the ventricles depolarize so fast the QRS complex characteristically looks thinner than the other parts of the ECG.
If the Q wave is not present the QRS complex should be measured from the next identified deflection which will usually be the R wave.
The J point is the junction of the QRS to the ST segment, flat line that connects the QRS complex and the T wave.
The end of the S wave transitions into the ST segment
The point at which the QRS returns to the baseline is called the junction or J point. I

5. Variations in QRS Complexes
While the QRS is said to consist of positive deflections called R waves and negative deflections called Q and S waves, all three waves are not always seen
If there is no R wave, the complex is called a QS complex
If there is no Q wave, the complex is called an RS complex

6. Variations in QRS Complexes
Waveforms of normal or greater than normal amplitude are denoted with a large case letter, whereas waveforms less than 5 mm in amplitude are denoted with a small case letter (e.g., “q,” “r,” “s”)
Although there is only one Q wave, there can be more than one R wave and S wave in the QRS complex.

7. Variations in QRS Complexes
A positive impulse immediately following the R wave is called R prime (R′)
A double positive impulse immediately following the R wave is called double R prime (R″)
A negative impulse immediately following the S wave is called S prime (S′)
A double negative impulse immediately following the S wave is called double S prime (S″)

8. Examining QRS Complexes
Look closely at their characteristics, especially their location, configuration, and deflection

9. Measuring the QRS Complex
Starting point is where first wave of complex starts to move away from baseline
Ending point is where last wave of complex begins to level out (flatten) at, above, or below the baseline
referred to as the J point

10. Measuring the QRS Complex
Determining where the QRS complex ends can be difficult as sometimes there isn’t a clear transition
Measurement of the QRS complex should include the entire S wave but it shouldn’t overlap into the ST segment or the T wave
Question to ask: “What is the normal duration of the QRS complex?”
Answer: The normal duration of the QRS complex is 0.06 to 0.10 seconds.
Instructional point:
It is helpful to look for the end of the QRS complex in as many leads as possible as it can sometimes be seen it in one lead but not another. Determining where the QRS ends can be difficult, particularly when there is depression or elevation of the ST segment. Look for a small notch, slope, or other movement that suggests an alteration of electrical flow. Q I

11. Evaluating QRS Complexes
Instructional point:
The algorithm can be used to categorize the various types of QRS complexes.
Identifying the presence of QRS complexes and determining whether they are normal or abnormal helps determine what rhythm the patient may be experiencing I

12. Normal QRS Complexes
QRS complexes should appear normal (upright and narrow) if:
the rhythm is initiated from a site above the ventricles
conduction has progressed normally from the bundle of His, through the right and left bundle branches, and through the Purkinje network
normal depolarization of the ventricles has occurred

13. Normal QRS Complexes
Seen with normal sinus rhythm and dysrhythmias that arise from above the ventricles provided there is not a conduction delay through the ventricles or other type of abnormality

14. Abnormal QRS Complexes
Produced by abnormal depolarization of the ventricles
Pacemaker site can be the SA node, or an ectopic pacemaker in the atria, AV junction, bundle branches, Purkinje network, or ventricular myocardium
Shape can vary from normal, tall, low amplitude, wide and bizarre-looking or slurred and notched

15. Abnormal QRS Complexes
Caused by a number of factors including:
Ventricular hypertrophy
Intraventricular conduction disturbance
Aberrant ventricular conduction
Ventricular preexcitation
Ventricular ectopic or escape pacemaker
Ventricular pacing by cardiac pacemaker

16. Tall QRS Complexes Usually caused by:
hypertrophy of one or both ventricles
an abnormal pacemaker
aberrantly conducted beat

17. Low-Voltage QRS Complexes
Seen in:
obese patients
hyperthyroid patients
pleural effusion

18. Wide-Bizarre Looking QRS Complexes
Often result from intraventricular conduction defect such as right or left bundle branch block

19. Aberrant Conduction
Occurs when early electrical impulses reach the bundle branch while it is still refractory after conducting a previous electrical impulse
Results in early impulse traveling down the unaffected bundle branch followed by the stimulation of the other bundle branch
Causes QRS complex to appear wider than normal

20. Ventricular Preexcitation
Occurs when an impulse arises from a site above the ventricles but travels through an abnormal accessory conduction pathway to the ventricles
Results in an abnormally wide QRS complex (greater than 0.10 seconds)
It also has characteristically abnormal slurring at its onset
Referred to as a delta wave

21. Pacemaker-Induced QRS Complexes
Generally ≥ 0.12 seconds in width and appear bizarre
Preceding each pacemaker-induced QRS complex is a pacemaker spike

22. Ventricular Dysrhythmias
Originate from the ventricular tissue

23. QRS Complexes of Ventricular Origin
Key characteristics of ventricular dysrhythmias
Wide
Bizarre-looking
T wave that takes an opposite direction to R waves

24. QRS Complexes of Ventricular Origin
Can be produced by early beats that arise from the ventricles before SA node can fire

25. QRS Complexes of Ventricular Origin
Seen with a sustained escape rhythm having a rate of 20 to 40 beats per minute (may be slower)
Instructional point:
Idioventricular rhythm arises from the ventricles when stimuli from the SA node, AV junction fail to reach the ventricles or their rate falls to less than that of the ventricles. I

26. QRS Complexes of Ventricular Origin
Seen with tachycardia that arises from the ventricles
Three or more early ventricular beats in a row
May come in bursts of 6 to 10 complexes or be sustained at rate of between 100 and 250 BPM
Instructional point:
Ventricular tachycardia results from rapid depolarization of the ventricles that overrides the SA node. I

27. Changing Ventricular Waveforms
Seen with tachycardia arising from more than one ventricular focus
Appears as a series of QRS complexes that rotate about the baseline between upright deflections and downward deflections
Produces a “spindle-like” appearance of the ECG rhythm

28. Wide QRS Complexes May be seen in severe forms of AV heart block
Location of the ventricular escape pacemaker site determines appearance of the QRS complex
Instructional point:
Wide, large (bizarre looking) QRS complexes indicate the ventricles are likely being paced by a ventricular focus. I

29. Chaotic Wavy Line Called ventricular fibrillation
Represents erratic firing of multiple sites in the ventricles
On ECG monitor it looks like a chaotic, wavy line with no discernible waveforms
Instructional point:
Ventricular fibrillation causes the heart muscle to quiver, instead of contracting and pumping blood throughout the body.
Defibrillation is considered the definitive treatment of ventricular fibrillation and must be delivered promptly. I

30. Flat (or Nearly Flat) Line
Called asystole
Represents lack of any cardiac activity in the ventricles
Complete cessation of cardiac output

31. Practice Makes Perfect
For this tracing, determine the type of ventricular waveforms
Answer: Normal QRS complexes at 0.08 seconds in duration
Ask students to determine rate, rhythm and type of atrial waveform as well. I

32. Practice Makes Perfect
For this tracing, determine the type of ventricular waveforms
Answer: RS complexes at 0.08 seconds in duration
Ask students to determine rate, rhythm and type of atrial waveform as well. I

33. Practice Makes Perfect
For this tracing, determine the type of ventricular waveforms
Answer: normal QRS complexes at 0.08 seconds, with early beats wide bizarre QRS complexes at 0.24 seconds in duration
Ask students to determine rate, rhythm and type of atrial waveform as well. I

34. Practice Makes Perfect
For this tracing, determine the type of ventricular waveforms
Answer: wide bizarre QRS complexes at 0.16 seconds in duration
Ask students to determine rate, rhythm and type of atrial waveform as well. I

35. Practice Makes Perfect
For this tracing, determine the type of ventricular waveforms
Answer: totally chaotic waveforms, no QRS complexes
Ask students to determine rate, rhythm and type of atrial waveform as well. I

36. Summary
Another important step of analyzing an ECG rhythm is examining the QRS complexes
QRS complex starts where first wave of complex starts to move away from the baseline and ends at the point where the last wave of the complex transitions into the ST segment
QRS complex is larger than the P wave because ventricular depolarization involves a considerably larger muscle mass than atrial depolarization.

37. Summary
Amplitude of a normal QRS is 5 to 30 mm and the duration is 0.06 to 0.10 seconds
Q wave is first negative deflection from baseline following the P wave
R wave is the first positive deflection following the Q wave (the P wave if Q wave is absent)
S wave is first negative deflection that extends below the baseline in the QRS complex following the R wave

38. Summary
Normal sinus rhythm and dysrhythmias that arise from above the ventricles will usually have normal QRS complexes
Abnormal QRS complexes are produced by abnormal depolarization of the ventricles
Duration of an abnormal QRS complex is greater than 0.10 seconds

39. Summary
Shape of an abnormal QRS complex varies from almost normal to wide and bizarre and/or slurred and notched.
Tall QRS complexes are usually caused by hypertrophy of one or both ventricles, or by an abnormal pacemaker or aberrantly conducted beat.
Low voltage or abnormally small QRS complexes may be seen in obese patients, hyperthyroid patients and pleural effusion.

40. Summary
Wide, bizarre QRS complexes of supraventricular origin are often the result of intraventricular conduction defect which usually occurs due to right or left bundle branch block
Wide QRS complexes may be seen in aberrant conduction, ventricular preexcitation and with a cardiac pacemaker

41. Summary
Wide, greater than 0.12 seconds in duration, QRS complexes are the key characteristic seen with ventricular dysrhythmias
With torsades de pointes the shape of the ventricular waveforms changes. It has a “spindle-like” appearance of the ECG rhythm
Instructional point:
The QRS complexes are usually bizarre-looking and the T waves take an opposite direction to the R waves. I

42. Summary
3rd-degree AV heart block is another dysrhythmia where there may be abnormal QRS complexes
Ventricular fibrillation appears on ECG monitor as a chaotic wavy line, with no discernible waveforms