Heart Blocks

Question 1

What are the rules/characteristics of Sinus Rhythm?

Answer 1

• Originate in the sinoatrial node
• P-wave normal, uniform, & upright in lead II ( will also be I, & V4-6)
• Regularity: regular (R-R are =)
• Rate: vary 60-100 bpm for “normal” sinus rhythm
• P-wave: one P-wave in front of every QRS
• PR interval: 120 – 200 msec (0.12- 0.2 sec) 3-5 blocks and constant
• QRS: < 120 msec ( less than 3 blocks)

Question 2

What are the different types of Sinus Rhythm?

Answer 2

- Normal sinus rhythm -
Rate 60 – 100 bpm
- Sinus bradycardia (SB)
Rate < 60 bpm
- Sinus tachycardia (ST)
Rate > 100 bpm
- Sinus arrhythmia (SA)
Regularly Irregular
Rate 60 – 100 bpm

Question 3

Type of block where the SA node may temporarily fail to pace and then restart with same pacing?

Answer 3

Sinus block or Sinus Arrest

Question 4

Umbrella term commonly used to refer to arrhythmias caused by SA node dysfunction?

Answer 4

Sick Sinus Syndrome (SSS)

Question 5

Sick Sinus Syndrome is commonly seen in which patient demographic?

Answer 5

• elderly who have heart disease
• pts with Sinus bradycardia without escape beats
• young healthy athletes due to excessive parasympathetic stim depresses SA node, atria and junction causing “pseudo SSS”

Question 6

What are the types of AV Heart Blocks?

Answer 6

• 1st degree
• 2nd degree type I or Wenckebach
• 2nd degree type II or Mobitz
• 3rd degree

Question 7

Which part of the EKG is used to determine if an AV block is present?

Answer 7

The P-R Interval (PRI)

Question 8

What is the normal length of a PR-Interval?

Answer 8

120 - 200ms or 3 - 5 small boxes

Question 9

A constant PRI > 0.2 seconds (200ms) with no dropped beats is indicative of which type of block?

Answer 9

1st degree AV Heart block

Question 10

What are the characteristics of a 1st degree AV Block?

Answer 10

• Regularity: R to R regular
• Rate: variable depending on underlying rhythm
• Normal P-wave: normal, upright in appropriate leads, one P for every QRS
• PRI: > 200 msec; constant (.20 sec) (5 blocks)
• Normal QRS: < 120 msec (0.12 sec) (3 blocks)

Question 11

What are the characteristics of 2nd degree AV heart Block?

Answer 11

• PRI > 0.2 secs or 5 small boxes
• P waves > QRS waves due to blocking of some of the impulses
• Normal QRS wave

Question 12

What are the two kinds of 2nd degree AV heart blocks?

Answer 12

Type I - Wenckebach

Type II – Mobitz

Question 13

What are the characteristics of a 2nd degree AV heart Block type I?

Answer 13

Wencheback:

• Characteristic lengthening of P-R interval
• Regularity: irregular
• Rate: variable depending on underlying rhythm
• P-wave: normal, upright, will be more than one P for the number of QRS; not 1:1 ratio; 2p :1 QRS, 3 P :2 QRS, 4:3 etc
• PRI: progressively lengthening PRI until one P blocked and no QRS follows
• QRS: < 120 msec (normal when present)

Question 14

What are the characteristics of a 2nd degree AV heart Block type II?

Answer 14

• Characteristic fixed P-R interval until a beat is dropped.
• Regularity: irregular
• Rate: variable depending on underlying rhythm
• P-wave: normal, upright, more than one Ps than QRSs
• PRI: constant until a P-wave in not conducted
• QRS: < 120 msec (can have a wide QRS)

Question 15

Which type of 2nd degree AV block is associated with disease of the distal conduction system (Bundle of His and Purkinje fibers) and can be life threatening?

Answer 15

• Type II Mobitz

- gives no warning of when the the QRS wave will drop and can become 3rd degree AV block

Question 16

How can you differentiate between a type I and type II 2nd degree AV block?

Answer 16

• have pt perform the valsava maneuver or perform a carotid massage
• is a type I if the # of cycles increases (ex: 2:1 to a 3:2)
• if no change or a 1:1 AV conduction is seen then it is a type II

Question 17

What are the characteristics of a 3rd degree AV block?

Answer 17

• AKA Complete AV block
• no association of P to QRS waves
• Regularity: R to R regular
• Rate: usually < 40, but can be b/t 40 to 60 bpm
• P-wave: more Ps than QRSs
• PRI: unable to determine, no relationship b/t P to QRS
• QRS: usually > 120 msec

Question 18

What is a 3rd degree AV block with a junctional focus?

Answer 18

• When the AV block occurs in the AV node above the AV junction
• Junctional focus will pace the ventricles at a rate of 40-60 BPM
• QRS is usually narrow

Question 19

What is a 3rd degree AV block with a ventricular focus?

Answer 19

• When the AV Block is below the AV junction causing an AV dissociation
• The Ventricles pace at rate of 20-40 BPM
• The QRS is wide and looks like a PVC, but is not premature

Question 20

What are the characteristics of a Bundle Branch Block (BBB)?

Answer 20

• wide QRS (> 120 msecs or > 3 boxes)

- two R-waves appear on some lead

Question 21

How do you differentiate between an incomplete and complete Bundle Branch Block (BBB)?

Answer 21

• Incomplete bundle branch block has a QRS interval between 101 – 119 msec
• Complete BBB has a QRS interval > 120 msec (3 small boxes)

Question 22

What are the characteristics of a Right Bundle Branch Block (BBB)?

Answer 22

• QRS > 120msecs (3 boxes)
• look at leads V1 & V6
• two R-waves in lead V1 (rabbit ears)
• slurred or rounded S wave in V2

Question 23

What are the characteristics of Left Bundle Branch Block (BBB)?

Answer 23

• QRS > 120msecs (3 boxes)
• wide distorted QRS complex in leads V1 & V6
• single R-waves, no rabbit ears

Question 24

In what lead(s) are saw tooth flutter waves seen on an ekg during Atrial Flutter?

Answer 24

in leads II, III and aVF