Basic ECG Flashcards
What is the conducting pathway of the heart?
- SA node
- Anterior, posterior, and middle fascicles
- AVN
- Bundle of His
- Right bundle branch (RBB) and left bundle branch (LBB)
- Purkinje fibers
What are the 3 types of cardiac cells?
- Pacemaker Cells
‒Determine the heart rate and initiate heart beats - Electrical Conducting Cells
‒Deliver the impulse to the myocardial cells - Myocardial Cells
‒Contract and pump blood out of the heart
What are the two types of pacemaker cells?
- SA node (SAN)
- This is the primary pacemaker of the heart (is responsible for setting the heart rate)
- The SA node rate is 60-100 beats per minute (bpm) - AV node (AVN)
- The AV node becomes the pacemaker if for some reason the SA node fails
- The AV node rate is 40-60bpm
If the AV and SA node fail, what sends the impulse to contract?
Myocardial cells transmit current more slowly (less effectively) than electrical conducting cells
What is a normal QRS complex?
What leads to a wide QRS complex?
When current travels through the muscle, current transmission is a lot slower, and this leads to a “wide” (normal) QRS complex
What are leads 1 and 2?
What is a 3 lead ECG?
A 3 lead ECG utilizes electrodes on the right arm, left, arm, and left leg
Lead 1
Lead I (white to black) detects the electrical difference between the right arm (-) and left arm (+)
Lead 2
Lead II (white to red) detects the electrical difference between the right arm (-) and left leg (+)
Lead 3
Lead III (black to red) detects the electrical difference between the left arm (-) and left leg (+)
5 Lead ECG
What does a small and large box indicate on ECG paper?
5 large boxes
‒1 second
300 large boxes
‒1 min
What is this patients heart rate?
HR will be 300 divided by the number of large boxes between each beat
So… ~140bpm
Label waves, segments, and intervals in a ECG wave
What does a p wave represent?
What does a QRS complex represent?
What can cause a wide QRS complex?
- The heart muscle gets “irritated” (which can happen with ischemia, pH imbalance, electrolyte abnormalities, caffeine, stress, etc)
- This can cause “premature ventricular contractions” (PVCs), which are visible on the ECG - The electrical conduction system fails, and the ventricles have to take over as the pacemaker of the heart
- This is known as a “ventricular escape rhythm” on the ECG - Current traveling across the myocardium, instead of through the Purkinje system
- This can happen in Wolf Parkinson White syndrome or in right bundle branch blocks (RBBBs) and left bundle branch blocks (LBBBs)
What does a t wave represent?
What does a u wave represent?
What does a j wave represent?
A “J wave” is a “bump” on the S wave, and is seen in hypothermia
What is a normal PR interval?
A normal PR interval is 120-200msec (3-5 small boxes)
‒This tells us that conduction is delayed in the AV node, which allows the atria to finish contracting before the ventricles contract (which allows optimal ventricular filling)
What is a premature beat?
A beat that happens before it should
‒Examples include premature atrial contractions (PACs), premature junctional contractions (PJCs), and premature ventricular contractions (PVCs)
Escape beats
Heart beat that happens after a long pause
-Ventricular escape and junctional escape beats
Factors that can reduce ventricular filling? (3)
- Heart beat that occurs without an atrial contraction
- Premature heart beats
- Rapid heart beats
Treatment for sinus tachycardia
- Give fluids if caused by hypovolemia
- Deepen the anesthetic
- Consider a B-blocker if not other options
Ectopy
Any heart beat that originates outside the SA node
- AV node
- Atrial myocardium
- Ventricular myocardium
Premature Atrial Contraction (PAC)
How often are they happening?
- Upright p wave
- Normal/narrow QRS complex
Atrial flutter
- Saw tooth pattern of 250-350 p waves/min
- More P waves than QRS complexes
Atrial fibrillation
- No p waves
- Irregularly irregular rhythm
Atria are just chaotically quivering with up to 500 atrial impulses/min
- Risk of blood clotting
- Cardiac output can decrease by 25-30% causing hypotension
Premature junctional contraction (PJC)
Premature beat
- Missing or inverted p wave
- Normal QRS complex
Level of concern is how often it is happening
Junctional rhythm
Beat or rhythm is originating in the AV node
- Inverted or absent p wave
- Normal QRS complex
Normal = 40-60bpm
Accelerated = 60-100bpm
Junctional tachycardia = >100bpm
Junctional escape beat
Escape beat with junctional properties
- Inverted or absent p wave
- Normal/narrow QRS complex
Premature ventricular contractions (PVCs)
- No p wave
- Wide, “bizarre” or “different” QRS complex
Concerned with frequency, can develop into V-tach
Treatment:
- Antiarrhythmics (lidocaine or amiodarone)
- Sometimes they go away by speeding up the heart with robinul
Ventricular Escape Beats
- Long pause followed by a ventricular beat (wide QRS complex)
- No P wave
- Similar to junctional escape beat (no P wave), but the QRS complex is wide
Venticular tachycardia
- No P waves
- Wide complex QRS
- Heart rate >100bpm
Treatment:
- Antiarrhythmics (amiodarone, lidocaine)
- Electrical cardioversion
Summary of premature beats
Ventricular fibrillation
The ventricles aren’t contracting, but are rather “quivering” at a very rapid rate, which means:
- The heart is consuming a lot of oxygen
- There is no pulse or cardiac output
Treatment:
- Defibrillation
- CPR until a perfusing rhythm returns
1st degree AV block
Long PR interval (>200msec, or 1 large box)
Period. End of story.
2nd degree AV block
“Dropped” QRS complexes
‒Sometimes two in a row can be dropped
There are 2 types of 2nd degree heart block:
- Mobitz Type I (Wenckebach)
- Mobitz Type II
Type I 2nd Degree AV Block (Wenkebach)
- Dropped QRS complexes
- Increasingly longer PR intervals before the QRS is dropped
Type II 2nd Degree AV Block
- Dropped QRS complexes
- Constant (unchanging) PR interval before the QRS complex is dropped
3rd degree AV block
Here, there are P waves and QRS complexes, but they are not associated with one another(this is referred to as “atrioventricular dissociation”)
‒It has been described as an ECG with “wandering” P waves
The ventricular rate is usually slow (≈30-40bpm)
Complete heart block
- ST segment changes
- Abnormal T waves
- Abnormal Q waves
