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Wednesday, June 2, 2010

EKG interpretation made easy

This post is meant as a means of using EKGs and rhythm strips in your critical thinking skills. It is not meant to replace a basic course in EKG and rhythm strip interpretation. However, it should help you in that regard.

You should be able to look at an EKG and not just see the basic interpretation, but use that EKG to help you generate a better overall picture of the patient's condition. Whereas #1 on this list shows you how to spot a possible pulmonary embolism.

EKG and rhythm strip interpretations:

1. Pulmonary Embolism:

  • a. S wave in lead I
  • b. ST depression in lead II
  • c. Large Q wave in lead III
  • d. T wave inversion in lead III
2. Basics:
  • a. ST depression = acute blood loss
  • b. Q Wave makes diagnosis of infarct
  • c. Q wave one small square is MI
  • d. Inverted T-wave is ischemia
3. Posterior wall Infarct:
  • a. ST depression in V1 & V2 if acute
  • b. Large R in V1 and V2
  • c. Maybe Q in V6
  • d. Inverted mirror test V1 & V2
4. Lateral wall Infarct:
  • a. Q in leads I and AVL (V5, V6)
5. Inferior wall Infarct:
  • a. Q in leads II, III, & AVF
  • b. ST elevated if acute
6. Anterior wall Infarct:
  • a. ST elevation V1 & V2
  • b. Q in V1, V2, V3 or V4
  • c. V1 & V2 = Anterioseptal
  • d. V3 & V4 = Anteriolateral
7. SVT: Narrow QRS & rate of 150-250

8. Left Bundle Branch Block: 2 R waves in V5 & V6

9. Right Bundle Branch Block:
  • a. 2 R waves in V1 & V2
  • b. QRS wide and looks like an M
10. Acidosis: Smaller amplitude

11. COPD: Small amplitude, Right axis deviation

12. Pulmonary Hypertension: Large P waves. This will also indicate end stage COPD with cor pulmonale or end stage pulmonary fibrosis, etc.

12. 1st degree heart block: (block is when pr interval is greater than five small boxes or 0.2seconds)
  • a. Prolonged pr interval and that's it.
  • b. For every p wave you have a QRS to follow it.
  • c. Rate may be slow, but no missed beats
  • d. The ratio of p waves to QRS's is 1:1
  • e. electrical conduction slightly delayed
  • f. Common in athletes, teens, young adults, heart disease, sarcoidosis, or drugs such as as beta-blockers, diltiazem, verapamil, digoxin, Lanoxin, and amiodarone.
  • g. rarely causes symptoms
13. 2nd degree block type or Mobitz I: (electrical conduction intermittenly blocked)
  • a. PR interval becomes progressively longer until 1 QRS skipped.
  • b. blocked QRS after every 2-5 QRSs
  • c. p-QRS usually goes like this: 1:1, 1:1, 1:1 2:1
  • c. QRS may be normal or wide if BBB
  • d. heart rate slow, irregular or both
14. 2nd degree type II or Mobitz II (Winkebach):
  • a. p waves for each QRS at ratio of 2:1, 3:1 or 4:1.
  • b. Often wide
  • c. Constant p to QRS ratio
15. 3rd degree heart block: (Electrical conduction completely blocked)
  • a. no impulses from the atria reach the ventricles
  • b. the ventricular rate and rhythm are controlled by the atrioventricular node
  • c. Rate = 30-50
  • d. p waves do not ever match up with QRS waves (no correlation)
  • e. serious arrhythmia that can affect the heart's pumping ability
  • f. Fatigue, dizziness, and fainting are common
16. Left Bundle Branch Block:
  • a. 2 R waves in V5 and V6
  • b. Cannot diagnose infarct
  • c. Same as anterior Hemiblock = posterior hemiblock which is also same as biphasicular block
17. Right Bundle Branch Block:
  • a. 2 R waves in V1 and V2
  • b. QRS is wide and looks like an M
18. Anterior Hemiblock:
  • a. Q in lead I and S in III
  • b. QRS slightly widened
  • c. Occurs in left anterior descending of RCA with MI and heart disease Causes Right Axis Deviation
  • d. May be associated with RBBB
  • c. 50% of posterior MIs
19. Posterior Hemiblock:
  • a. S in 1 and Q in 3
  • Normal or slightly widened QRS
  • Occurs in Right anterior descending of RCA with MI or heart disease
  • Causes Right Axis Deviation
  • Rule out other causes of RAD
  • Rare, causes AV block, deadly
20. Bifasicular Block:
  • a. A combination of blocks
  • b. Anterior Hemiblock + RBBB
  • c. posterior Hemiblock + RBBB
  • d. Anterior Hemiblock + Posterior Hemiblock (also called LBBB)
  • May cause intermittent AV block

21. Axis Deviation of the heart*: This is the general direction the electrical signal takes from the AV nodes through the ventricles. The direction of depolarization (vector) and size of the QRS arrow (amplitude) change with certain disease processes.

If the axis is not depolarizing normally, this can help clue you in to underlying pathology. For more, check out this link to understanding axis deviation. Check out this link to help you determine underlying pathology using this hexaxial reference.
So, to determine axis, check out the hexaxial reference. Examine the QRS complex in the limb leads (I, II and III). Now find the one that has the largest deflection (amplitude). Now determine if it's upright (positive) or downward (negative).

If the largest amplitude is lead II, and the amplitude is positive, then you know you have an axis deviation of about +60, which is normal. If, on the other hand, the amplitude was negative, then the deviation is about -120, which is severe right axis deviation.

It's that simple. If you look at the standard EKG, the axis will be noted, so you shouldn't even have to use this hexaxial reference.

Basically, if the QRS is upright (positive) in the lead with the most voltage, the mean axis must be very close to the position of this lead on the circle. If the QRS complex is downward (negative), the mean axis must be located in the opposite direction from the location of this lead on the hexaxial circle.

Now determine axis (again, this should be noted on the EKG):
  • Normal axis is 0 to +90 degrees.
  • Left Axis deviation is anything between 0 and -90
  • Right Axis deviation is between +90 and 180
22. Right Axis Deviation: (axis between 9 and -90)
  • a. QRS negative in lead I
  • b. QRS positive in AVF
  • c. QRS negative in AVF and lead I if extreme RAD
  • d. QRS in V1, V2 isoelectric
  • e. Slender person with ventricular heart
  • f. Ventricular hypertrophy
  • g. Pulmonary disease
  • h. MI on left side of heart
  • i. Q-wave of inferior MI
  • j. Pulmonary embolism
  • k. Anteriolateral MI
  • l. Emphysema
23. Left Axis Deviation: (axis between +90 and 180)
  • a. QRS positive in lead I
  • b. QRS negative in AVF
  • c. QRS in V5 and V6 are isoelectric
  • d. Obese patients
  • e. Left Ventricular Hypertrophy
  • f. MI right side of heart
24. Severe Right Axis Deviation: (Axis between -90 and -179)
  • Called no mans land
  • Severe Left Axis Deviation
  • Emphysema
  • Lead Transposition
  • Artificial cardiac pacing
  • Ventricular tachycardia
25. Left Ventricular Hypertrophy:
  • a. QRS complexes with exaggerated amplitude both in height and depth
  • b. S wave in V1 is deep, large R in v5
  • c. Height of S in V1 + R in V5 = or greater than35 mm
  • d. T wave inversion in V5 and V6 with a gradual downward slope
26. Hyperkalemia: Flat p waves, wide QRS, peaked T

27. Hypokalemia: Flat T waves, wide QRS, u waves

28. Hypercalcemia: QT interval shortens

29. Hypocalcemia: Prolonged QT interval

30. Digitalis effect:
  • a. PABS early sign
  • b. gradual down-sloping of ST segment
  • c. Low K enhances Digitalis effect
31. Quinidine Effects: (Anti-arrhythmic)
  • a. Widening of p waves and QRS
  • b. Often ST depression, prolonged QT
  • c. Maybe presence of U wave
32. Atrial Fibrilation:
  • a. Quite common in patients with lung diseases.
  • b. Due to the excess workload the heart eventually switches to this rythm, such as COPD, CHF, etc.
  • c. Irregular rythm, although one p for every QRS
33. Sinus tachycardia: Rate greater than 100 but less than 150 (greater than 150 = SVT)

34. Atrial Flutter: Sawtooth appearance of rythm strip

35. Junctional Rythm: No p waves, or p waves go in various directions.

36. Sinus bradycardia: Rate less than 60

37. Preventricular contraction (PVC):
  • a. An abarrently conducted beat generated by the ventricles.
  • b. They disrupt the regular rythm.
  • c. pt may feel palpitations, or heart flutters
  • d. Causes: chemical imbalances, meds, alcohol, caffeine, increased adrenaline (excited), exercise, anxiety, injury to heart muscle, tobacco use,
  • e. May be normal, but if canstant may lead to other arythmias
38. Bigeminy: Pre ventricular contraction every other beat

39. Ventricular tachycardia:
  • a. Three or more beats of ventricular origin.
  • b. Wide comlex
  • c. There are no normal-looking QRS complexes.
  • d. The rhythm is usually regular, but on occasion it may be modestly irregular
40. Atrial Fibrillation:

  • The most common arrhythmia.
  • It's caused by the atria quivering in random spots
  • Resulting in many p-waves and irregular irregular QRS complexes
  • Pulse will also be irregularly irregular
  • P-waves may be so fine the baseline appears wavy and fine
  • 8% of people over 80 have it (risk increases with age)
  • Risk also increases with chronic lung disease due to enlarged atria
  • If have large heart, usually becomes chronic and is not treated
  • Generally asymptomatic and in itself is not life threatening (often becomes chronic)
  • Increased risk of stroke as blood may pool in heart and clot, resulting in a PE
  • Often heart rate is greater than 100 but less than 150
  • If heart rate less than 120 may be no symptoms
  • Fibrillatory waves best seen in leads II, III, and VI
  • Common cause is heart failure, alcohol abuse, infections (pneumonia), paricarditis, sick sinus syndrome, pulmonary embolism, recent surgery,
  • Treated by treating the cause
  • Cardioversion if life threatening (hypotension, pulmonary edema) and young person with normal heart function
41. A-fib with rapid ventricular response:
  • Rate is greater than 100 and less than 150
  • If patient unstable, cardioversion is necessary
  • If stable, treat with digoxin or verapamil
  • Goal to reduce rate to between 80 to 100 BPM
  • If chronic, calcium antagonists (verapamil or diltiazem) or beta blockers are adjusted to maintain optimal heart rate.
42. Atrial Flutter:

  • EKG or rhythm strip has a saw tooth patern
  • Heart rate 100-150
  • If heart rate less than 120 may be no symptoms
  • Occurs most rapidly in patients with cardiovascular disease (hypertension, coronary artery disease, cardiomyopathy)
  • Not stable, and frequently changes into atrial fibrillation
  • Pooling of blood may result in clots
43. Pre-ventricular contraction (PVC):
  • Originates in irritable focus in ventricles
  • Produces giant ventricular processes on EKG
  • Easily recognized by enormous amplitude in both height and depth
  • Most likely cause is hypoxia
44. Ventricular Bigeminy: A PVC occurs every other beat (poor oxygenation)

45. Ventricular Trigeminy: A PVC occurs every third beat. (poor oxygenation)

46. Ventricular Quadrigeminy: A PVC occurs every fourth beat. (poor oxygenation)

47. Supraventricular Tachycardia: Heart rate 150 to 250
  • Rapid, PVC like complexes that are narrow (narrow indicates external cause)
  • Caused by irritable focus above ventricles
  • Causes: stress, smoking, alcohol abuse, pneumonia, heart failure, chronic lung disease, PE, paricarditis, cocaine, digitalis, asthma medicine, cold remedies
  • Symptoms: palps, dizziness, SOB, anxiety, chest pain
  • May resolve on own or with treatment (cardizem) or with valsalva meneuver, squeezing balls, putting pressure on carotid arteries, ice on balls, etc.
  • shockable is symptomatic
48. Ventricular Fibrillation:

  • May be coarse or fine
  • Does not provide adequate oxygenation to tissues of body
  • Is a shockable rythym with 300 joules '
  • EKG tracing totally eratic
  • Cardiac Arrest
49. Ventricular Tachycardia:

  • More than 3 PVCs in a row
  • wide complex QRS
  • Rate greater than 100
  • Causes: heart failure, heart surgery, valve disease
  • Is a shockable rhythm with 300 joules during ACLS
  • The earlier shocked, the better the results
  • Poor perfusion (heart not pumping enough blood to support life)
50. Torsades de Pointes:

  • Rapid Ventricular rythym caused by low potassium
  • Ventricular complexes twist up and down SSSSSSSssssssSSSSSSsssssSSSSSS
  • Rate 250 to 350 per minute
  • Polymorphic Ventricular Tachycardia (polymorphic means
  • Prolonged QT interval (wide QRS)
  • Wide QRS means the cause is within the heart
  • Causes are diahrea, alcoholics, hypokalemia, malnourished, poverty
  • Treatment is magnesium sulfate
  • See picture here
How to determine heart rate:

According to elementary EKG, "You take the duration between two identical points of consecutive ECG waveforms such as the R-R duration. Take this duration and divide it into 60. The resulting equation would be:

"Rate = 60/(R-R interval)"

However, "A quicker way to obtain an approximate rate is to go by the number of 5 small boxes (i.e., the size of one big box or the duration of 0.2 secs) that are in between the two identical points. For example, if the two points were 1 big box away, then the rate is approx 300 beats/min. The rest of the sequence would be as follows:
  • 1 big box = 300 beats/min (duration = 0.2 sec)
  • 2 big boxes = 150 beats/min (duration = 0.4 sec)
  • 3 big boxes = 100 beats/min (duration = 0.6 sec)
  • 4 big boxes = 75 beats/min (duration = 0.8 sec)
  • 5 big boxes = 60 beats/min (duration = 1.0 sec)"
I use the later, and I've never gotten a question about heart rate wrong on any test.

For a basic rhythm strip reveiw, click here.

For a basic EKG course, click here for the ECG learning center.

See the EKG library here.

* Reference for axis deviation hexaxial reference is "Respiratory Disease," ed. by Robert L. Wilkins and James R. Dexter, 1993, page 41.
Please note that I'm learning much of this as I research, so if you find something that's not accurate, or have a tip for making the process of learning easier, please let me know.
Updated August 2, 2010

Word of the day: Arcanum: Secret or esoteric knowledge, specialized information, a mystery; a secret and powerful remedy
EKG interpretation is not arcana wisdom known only to doctors.

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