Lecture 4

Question 1

long PR interval (>.20 seconds)

Answer 1

-atrioventricular blocs (1st, second, and 3rd degree)

Question 2

short PR interval (<0.12 seconds)

Answer 2

• preexcitation syndromes

- WPW and LGL

Question 3

long QRS interval (>0.12 seconds)

Answer 3

• bundle branch blocks
• fascicular blocks
• premature ventricular contractions (PVC)
• idioventricular rhythm

Question 4

long QT interval (>0.45 seconds)

Answer 4

• hypokalemia
• hypomagnesemia
• hypocalcemia

Question 5

Pre-excitation syndromes

Answer 5

• accessory pathways formed during cardiac development and can exist in a variety of anatomical locations
• early activation of the ventricles due to impulses bypassing the AV node via an accessory pathway
• wolff-parkinson-white (via bundle of kent)
• lown-ganong-levine (via james fibers)
• mahaim-type fibers

Question 6

accessory pathways

Answer 6

• can conduct impulses in many ways:
• anterograde (toward the ventricle)
• retrograde (away from the ventricle)
• both directions = majority of the time
• direction of conduction affects the appearance of the ECG

Question 7

effect of preexcitation syndromes

Answer 7

• can cause PSVT, ventricular fibrillation and sudden death

- recognize it on an EKG and save a life!

Question 8

WPW

Answer 8

• 1.5 per 1000 (50 to 60% become symptomatic)
• bimodal distribution (1st peak in early childhood, 2nd peak in young adulthood)
• sx: dizziness, palpitations, syncope, sudden death
• early activation of the ventricles = short PR

Question 9

WPW types

Answer 9

• type A (more common) - Kent’s fiber to LV criteria: WPW patterns with tall R waves in leads V1 and V2
• type B (much less common) - kent’s fiber to RV criteria: WPW patterns with predominantly negative RS or QS waves V1 and V2

Question 10

treatment of WPW

Answer 10

• stable/asymptomatic: cardiology referral
• symptomatic (PSVT, VF): DC cardioversion or unsynchronized
• radiofrequency catheter ablation - definitive tx: heats the tissue to destroy the accessory pathway

Question 11

bundle branch blocks

Answer 11

• recall ventricular depolarization = 0.08-0.12 seconds (2-3 small boxes)
• conduction defect - RBB or LBB (and/or fascicles)
• ventricle with BBB must await initiation by opposite ventricle (cell-to-cell basis): much slower activation, long bizarre shaped QRS-complexes

Question 12

Right bundle branch block

Answer 12

• RBBB
• more common
• use V1 and V6 for dx
• V1: wide positive QRS, RSR’, S down to baseline
• V6: wide slurred S wave

Question 13

Left bundle branch block

Answer 13

• LBBB
• less common
• use V1 and V5 or V6
• V1: QRS deeply negative
• V5, V6: QRS wide, RSR’
• difficult to dx MI
• New LBBB = possible MI

Question 14

Hemiblocks

Answer 14

• fascicular blocks (aka hemiblocks) - partial blocks in the LBB system
• left anterior fascicular block - left axis deviation
• left posterior fascicular block - right axis deviation
• NOT ALL LAD AND RAD ARE HEMIBLOCKS