8/4- Electrocardiography at the Bedside 1 Flashcards
What is the PR interval?
Segment from P wave from BEGINNING of the QRS complex (not R wave itself)
1 mm on the EKG corresponds to what?
1 mm = 40 ms (0.04 s) = small box
5 mm on the EKG corresponds to what?
5 mm = 200 ms (0.20 s) = large box
Normal P-R interval = length?
Normal P-R interval = 3-5 small boxes = 120-200 ms
Normal QRS interval = length?
Normal QRS interval = 2-3 small boxes = 80-120 ms
Normal QTc interval = length?
Normal QTc interval = 9-11 small boxes = 360-440 ms (400 +/- 40)
What does QTc refer to?
Corrected QT interval (corrected for heart rate)
Systematic Evaluation of 12 lead ECG (11)?
- Rhythm
- Rate
- QRS axis
- P wave morphology
- P-R interval
- QRS interval
- QT interval
- Chamber enlargement: LVH, RVH
- Pathologic Q waves
- ST and T wave changes
- Precordial R wave progression
What is the range of normal sinus rhythm?
60-100 per minute
What is the R-R interval?
Interval between 2 consecutive QRS complexes
What type of rhythm is shown here? Characteristics?
Atrial fibrillation (until proven otherwise)
- No P wave
- Rhythm is irregular
- Present QRS complexes
Heart rate assessment?
Divide 300 by the R-R interval expressed in number of “large boxes”
If the R-R interval is 400 ms or 2 “large boxes”, what is the heart rate?
HR = 300/2 = 150 bpm
P wave is usually positive in what leads?
P wave is usually positive in all ECG leads except aVR and V1
P wave results from what?
Early RA and late LA depolarization
Abnormal P waves are indicative of what?
- LA enlargement: bifid P wave “P-mitrale” due to delayed left atrial depolarization
- RA enlargement: tall P wave > 2.5mm
Best lead to assess P wave is what?
Lead II or III/aVF
What is this? What causes it?
Bifid or notched P wave in lead II
- Takes longer to fully depolarize the L atrium (delayed portion of P wave is due to longer LA depolarization)
What is this? What does it indicate?
Tall P wave > 2.5 mm in lead II
- Right atrial enlargment
What constitutes a prolonged PR interval? What causes it?
PR > 0.20s
- Block in the AV node delays AV conductions
What are some of the causes of PR elongation? (broadly, 3)
Acquired “reversible” causes
- Drugs
- Acute ischemia or infarction
“Irreversible” causes
- Degenerative or calcific disease of the conduction system (“irreversible”) called Lev’s or Lenegre’s disease
What drugs specifically may cause PR elongation?
- Beta blockers
- Ca channel blockers
- Digoxin
- Amiodarone
- Clonidine
What is Wolf-Parkinson Syndrome?
ECG Triad:
1. Short P-R interval (< 120 ms)
2. Delta wave: an abnormal extra + wave immediately before the QRS complex; slurred initial QRS upstroke
3. Wide QRS complex > 120 ms
Restated:
Syndrome associated with accessory bypass tract (bypassing AV node) which shortens the PR interval
- Also characterized by wide QRS complex (QRS > 0.12) and delta waves (pic s)
What happens to the QRS complex in BBB (bundle branch block)?
QRS complex will have early R wave and one late R’ wave, also called an RSR’ complex
- Will also be widened
((- An initial negative inflection of the QRS complex is the Q wave
- The first positive inflection of the QRS complex is the R wave
- The first negative inflection of the QRS complex is the S wave))
What is the key difference between R and L BBB?
Location of RSR’
RBBB: RSR’ in V1 or V2
LBBB: RSR’ in V5 or V6
What does a widened QRS complex with RSR’ show?
Bundle branch block (or dilation of the corresponding chamber)
(normal QRS = 80-120 ms = 2-3 small boxes)
What heart chamber is located closest to chest wall?
Right ventricle
What is this?
RSR’ in chest lead V1
What is this?
RSR’ in chest lead V2
What do these together indicate?
RSR’ in chest leads V1 and V2 (placed over RV chamber) indicating RBBB
What is this?
RSR’ in chest lead V5
What is this?
RSR’ in chest lead V6
What do these together indicate?
RSR’ in chest leads V5 or V6 (placed over LV apex) indicating LBBB
What causes bundle branch block?
- Ischemia or infarction of the bundle branch
- Eccentric hypertrophy of the ventricles
QT changes with what?
Heart rate
What is QTc? Normal value?
QT corrected for heart rate
- Varies from 360-440 ms
How do ewe calculate QTc?
Divide QT by square root of R-R interval
What causes prolonged QT interval (acquired)?
Drugs
- Anti-arrhythmics (class IA, IC, III)
- Anti-psychotic phenothizines
- Tricyclic antidepressants
- Antifungals
Electrolyte abnormalities: low K, Mg, or Ca (low K is the most common)
What causes prolonged QT interval (congenital)?
- Jervell and Romano Ward
What is this?
Torsades de Pointes
- (polymorphic ventricular tachycardia)
- Classic complication of Long QT syndrome
What does RAE (right atrial enlargement) cause?
Prominent early portion of P > 2.5
What does LAE (left atrial enlargement) cause?
Delayed late portion of P with a bifid P in II
What will be seen with RBBB? Which leads?
RSR in V1/V2
What will be seen with LBBB? Which leads?
RSR’ in V5/V6
What is normal QTc?
360-440
What can long QT lead to?
TDP VT (Torsades de Pointes)
What is WPW?
Syndrome associated with accessory bypass tract (bypassing AV node) which shortens the PR interval
- Also characterized by wide QRS complex (QRS > 0.12) and delta waves
What may cause long PR?
- Drugs (digoxin, BB, CCB)
- Ischemia or infarction
- Degeneration or calcification of AVN or His bundle
What may cause long QT?
- Drugs
- Electrolytes (low K, low Ca, low Mg)
Depolarization of the R atrium occurs in which part of the P wave?
A. Early
B. Late
C. Neither
Depolarization of the R atrium occurs in which part of the P wave?
A. Early
B. Late
C. Neither
Why is the R atrium depolarized earlier tan the L atrium?
A. Sinus node is int he L atrium
B. Sinus node is in the R atrium
C. AV node is closest to the R atrium
D. AV node is closest to the L atrium
Why is the R atrium depolarized earlier tan the L atrium?
A. Sinus node is int he L atrium
B. Sinus node is in the R atrium
C. AV node is closest to the R atrium
D. AV node is closest to the L atrium
All of the following drugs prolong the P-R interval except?
A. Beta blockers
B. Amiodarone
C. Ca channel blockers
D. Digoxin
E. Nitroglycerin
All of the following drugs prolong the P-R interval except?
A. Beta blockers
B. Amiodarone
C. Ca channel blockers
D. Digoxin
E. Nitroglycerin
Nitrates in general have no effect on AV conduction
Bundle branch block is characterized by all of the following except:
A. QRS interval > 120 ms
B. QRS interval smaller than 120 ms
C. RSR’ QRS in some chest leads
D. Delay in ventricular depolarization
Bundle branch block is characterized by all of the following except:
A. QRS interval > 120 ms
B. QRS interval smaller than 120 ms
C. RSR’ QRS in some chest leads
D. Delay in ventricular depolarization
WPW is characterized by all of the following except:
A. QRS interval > 120 ms
B. QRS interval smaller than 120 ms
C. Delta wave
D. Slurred initial upstroke of QRS
E. Accessory tract bypassing the AV node
WPW is characterized by all of the following except:
A. QRS interval > 120 ms
B. QRS interval smaller than 120 ms
C. Delta wave
D. Slurred initial upstroke of QRS
E. Accessory tract bypassing the AV node
