ECG: SVT, bundle branch, AV blocks - Hefnawy

Question 1

narrow and wide QRS in tachycardia

Answer 1

• anything above the bundle of HIS –> narrow QRS**

- anything below the bundle of HIS –> wide QRS**

Question 2

atrial tachycardia

Answer 2

• Ectopic foci can give you depolarization independent of SA node
• consistent P waves with single focal
• Variation in height/number of P waves with multifocal

Question 3

AVNRT

Answer 3

• signal going in circle in AV node and refiring atria

- depolarization wave going in opposite direction (bottom to top of atrium) –> inverted P wave due to vector

Question 4

AVRT

Answer 4

-Accessory bundle fibers traveling on other conductive fibers –> reentry tachycardia not involving the AV node

Question 5

sinus tachycardia vs. bradycardia

Answer 5

1. tachycardia
   - beats >100 bpm (high sympathetic tone)
2. bradycardia
   - beats <60 bpm (high parasympathetic)

both have narrow QRS, normal PR intervals, equal RR intervals and height

• relying on sinus
• can see changes in respiration

Question 6

ectopic beats

Answer 6

• spontaneous beats from other parts of the heart that affect sinus rhythm
• single electrical beats outside the sinus node

Question 7

supraventricular tachycardia

Answer 7

1. atrial ectopic beats
2. atrial tachycardia
3. junctional ectopics
4. atrial fibrillation
5. atrial flutter

Question 8

atrial ectopic beats

Answer 8

• depolarization triggered in atrium independent of sinus node –> premature P wave distorting the T wave
• sometimes missed beat bc AV node is in refractory period when atria depolarize again

Question 9

junctional atopics

Answer 9

• ectopic depolarization in at junction of atria and ventricles (typically AV node and surrounding area) –> inverted P wave (hidden by QRS) and narrow QRS
• may see absent P wave bc it happens early on
• inverted P wave due to depolarization of the atria in the opposite direction

3 variants: P wave can be hidden in the QRS, before, or after
-depolarization waves traveling to atria and ventricles at the same time in junctional

Question 10

atrial fibrillation

Answer 10

• ectopic depolarizations in all directions –> not measured on EKG bc of weak contractions –> lead to dilation of atrium
• usually at pulmonary veins entering LA –> treat with cauterization
• high risk of coagulation –> take anticoagulants
• no P wave –> fibrillation (f) waves instead (random, flat line)
• narrow QRS
• heart rate irregular

Question 11

atrial flutter

Answer 11

• ectopic depolarizations traveling in circle before entering other atrium
• HR more regular and predictive than Afib (larger F waves with more consistency)
• back to back F waves in leads V1-V3** –> sawtooth** bc not all depolarization can enter AV node
• look like P waves in leads V1-V3, sawtooth in inferior leads
• narrow QRS
• better outcome than Afib
• regularly irregular rhythm

Question 12

AVNRT (dual AV node) - SVT proper

Answer 12

• premature atrial P wave** –> stimulates slow path in AV node to bundle of HIS –> reaches bundle of HIS where fast track is now in refractory period stimulating it –> fires fast track back towards atrium to stimulate it again –> inverted P wave**
• treat with carotid massage (stimulates vagus nerve slowing down conduction) or Ca2+ channel blockers

Question 13

AVRT - SVT proper

Answer 13

• no AV node involvement
• triggered by premature beat
• Wolf-Parkinson White (bypass tract) –> accessory fibers that carry depolarizations straight to ventricles normally (seen as delta wave)
• orthodromic –> AV node working in right direction, but WPW working in opposite direction –> narrow QRS**
• antidromic –> WPW working in right direction, but AV node working in opposite direction –> wide QRS**
• retrograde P waves (if present) after QRS in both bc depolarization traveling in opposite direction
• retrograde P wave later than AVNRT

Question 14

ventricular tachycardia (VT) - 2 types

Answer 14

-more serious than SVT

1. monomorphic VT
   - most common type
   - rapid firing of ectopic foci in ventricles
   - QRS –> same shape, wide (longer time to depolarize), inverted (depol. in opposite direction), regular rhythm
   - discordant T waves
   - random P waves (not correlated with QRS)
2. polymorphic VT
   - inconsistent QRS complexes
   - caused by prolonged QT interval due to drugs
   - Torsade de Pointes
   - can lead to ventricular fibrillation and heart failure

Question 15

reentrant monomorphic VT

Answer 15

• paroxysmal –> not continuous
• rapid depolarizations –> inhibit other conduction paths
• slow rise in Na+/Ca2+ producing depolarization –> re-fire previous myocyte bc it is now in refractory period –> reentry
• depolarizations must spread cell to cell

Question 16

SA block

Answer 16

• SA node conduction block prevents impulses from leaving SA node –> no P wave or QRS
• pause in the EKG (short term)

Question 17

SA arrest

Answer 17

• SA node does not fire at all –> prolonged pause –> syncope, dizziness, unconscious bc heart is not pumping
• “sick sinus rhythm”

Question 18

escape junctional beat

Answer 18

• handy when you have SA arrest/pausing
• AV node or bundle of HIS starts firing at the AV junction –> backup of the heart to prevent long asystole
• inverted P waves (before, after, or masked)
• narrow QRS (wide if it occurs below the bundle of HIS)

Question 19

1st degree AV block

Answer 19

• prolonged but equal PR intervals (takes longer for depolarization to reach ventricle)**
• not a progressive increase in PR
• normal rhythm
• narrow QRS

Question 20

2nd degree AV block - Mobitz type I

Answer 20

• progressive increase in PR interval until 1 QRS beat drops (more Ps than QRS) –> reset PR after
• RR intervals get shorter
• QRS is narrow
• regularly irregular rhythm

Question 21

2nd degree AV block - Mobitz type II

Answer 21

• random QRS beat drop without a prolonged PR interval**
• no change in PR** (stationary)
• regularly irregular rhythm
• WIDE QRS** bc under the bundle of HIS (infra-Hissian lesion)

Question 22

2nd degree AV block - 2:1 block

Answer 22

• double the P waves compared to the R waves**
• lose R wave every 2nd beat –> regular rhythm**
• wide QRS (infra-Hissian)
• PR remains the same

Question 23

3rd degree AV block

Answer 23

• lose all conduction b/w atria and ventricles (no depolarization passing through AV nodes)
• regular but random P waves (not related to QRS)
• bundle of HIS or bundle branches act as pacemakers
• regular QRS –> wide if pacemakers below bundle of HIS
• most severe –> need electrical pacemaker

Question 24

bundle branch block

Answer 24

• either right or left bundle branches fail
• conduction normal on healthy side –> depolarizes contralateral ventricle

1. RBBB
   - wide QRS –> depolarize LV then RV
   - abnormal R transition
   - inverted T wave in V1-V3 (right pericardial leads)
   - tall + R in V1,V2
   - wide S in V6
2. LBBB
   - wide QRS
   - no growth of R from V2-V3 (short)
   - sudden R transition to left pericardial leads
   - upright short, notched QRS in V5,V6**
   - large, deep S in V1-V3**
   - inverted T waves in left pericardial leads