Qrs Complex

Question 1

What is a pathological Q wave

Answer 1

Any Q wave in leads v1, v2, v3 is pathological
In most other leads Q must be 1 box wide (>30ms)

Leads III and aVR normally have Q waves that can be any size

Question 2

What Q waves indicate MI

Answer 2

First of all to be an MI, the Q waves must meet the definition of pathological
Two or more contiguous leads with Q wave at least 1 box deep

Question 3

What are criteria for RVH

Answer 3

Tall R wave in V1, no official criteria

Question 4

What are criteria for LVH

Answer 4

R in aVL more than 11mm or > 18mm if left axis is present
R in V5 or V6 more than 26 mm
S in V1 or V2 + R in V5 or V6 more than 35

Question 5

What is a widened QRS complex

Answer 5

The longest limb lead QRS duration of over 100ms

Question 6

What are the criteria for a LAHB

Answer 6

Left axis deviation (usually -45 to 90 degrees)
qR complexes in I, aVL
rS in leads II, III, aVF
prolonged R wave peak time in aVL, > 45ms

Question 7

What are criteria for LPHB

Answer 7

Frontal plane axis between 90° and 180° in adults
· rS pattern in leads I and aVL
· qR pattern in leads III and aVF
· QRS duration less than 120 milliseconds

Question 8

What is differential diagnosis for prolonged QRS complex

Answer 8

RBBB
LBBB
LAHB
LPHB
Intraventricular conduction disturbance
Medications- maybe this should go under causes
Pre-excitation

Question 9

What leads should be checked to determine if QRS is normal duration

Answer 9

There is no standard
However most texts recommend limb leads. Precordial leads tend to have longer QRS.
So take the single longest QRS of the limb leads

Question 10

Is there one lead or more to check QRS duration?

Answer 10

You should check all limb leads. Because the beginning or end of any single QRS could have an isoelectric phase leading to a falsely low estimate. Choose the longest of the limb leads.

Question 11

What patient factors influence what is a normal QRS duration?

Answer 11

Male and younger age have longer durations. So a normal QRS can be as long as 115ms in a young male and as low as 100ms in an older female.

Question 12

What are criteria for LBBB

Answer 12

QRS greater than 120ms

In leads I, v5, v6=
delayed intrinsicoid deflection (beginning of QRS to peak R >.05 sec)
Broad monophonic R waves usually notched or slurred
Secondary st- t wave changed in opposition direction of QRS complex

Question 13

What are criteria for RBBB

Answer 13

QRS > 120 ms
Wide slurred S in lead I
Terminal R in V1
Should see a depolarization abnormality - not necessarily in all leads

Question 14

How would you tell if pre excitation is causing QRS prolongation?

Answer 14

There should be a shortened PR interval and possibly a delta wave