Harrison's Ch 228: ECG

Question 1

The smallest (1 mm) horizontal divisions on the ECG correspond to what time period?

Answer 1

0.04 seconds

Question 2

The heavier lined horizontal divisions on the ECG correspond to what time period?

Answer 2

0.20 seconds

Question 3

What does “deflection” refer to in an ECG?

Answer 3

The amplitude of a wave

Question 4

With standard calibration, how many mm= 1mV on an ECG?

Answer 4

10 mm = 1 mV

Question 5

What are the 4 major ECG intervals?

Answer 5

#RR 
#PR 
#QRS 
#QT

Question 6

How can the heart rate be calculated from the RR interval?

Answer 6

Divide # of large time units (0.2) between consecutive R waves into 300 or the # of small units (0.04) into 1500

Question 7

What does the PR interval measure? What is a normal PR interval?

Answer 7

#The time between atrial & ventricular depolarization.
#Normally 0.12-0.2 seconds

Question 8

What does the QRS interval measure? What is a normal QRS interval?

Answer 8

#Reflects duration of ventricular depolarization
#Normally ≤ 0.10 sec

Question 9

What’s the QT interval, anyway?

Answer 9

It measure the time of both ventricular depolarization & repolarization. It varies inversely with heart rate.

Question 10

How do you get a “corrected” QT interval, or a QTc?

What is a normal QTc interval?

Answer 10

#The QT interval divided by the square root of the RR interval, or QT/√RR
# ≤ 0.44 seconds

Question 11

The QRS is divided into specific deflections, or waves. What are they?

Answer 11

#If the intial deflection is negative, it's Q-wave
#First positive deflection is R-wave
#Negative deflection after R is S-wave

Question 12

What do you call an entirely negative QRS complex?

Answer 12

A QS wave

Question 13

Where do the 6 frontal plane leads go?

Answer 13

#V1: 4th intercostal just to the right of sternum
#V2: 4th intercostal just to left of sternum
#V3: Midway btwn V2 & V4
#V4: 5th intercostal space, midclavicular line
#V5: Anterior axillary line, same level as V4
#V6: Midaxillary line, same level as V4 & V5

Question 14

A normal P-wave will be positive & negative in what leads?

Answer 14

#Positive: Lead II
#Negative: aVR

Question 15

Activation of the atria by an ectopic pacemaker in the lower atrium or from the AV junction may produce what kind of P-waves?

Answer 15

#Negative in lead II
#Positive in aVR

Question 16

Right atrial overload (acute or chronic) may lead to what ECG finding?

Answer 16

• Increased P-wave amplitude

* Tall, peaked P-waves in limb or precordial leads

Question 17

Left atrial overload or enlargement may produce what ECG finding?

Answer 17

#Biphasic P-wave in V1 with a broad negative component, or	
#Broad, often-notched P-waves in 1 or more limb leads	
#Often called "left atrial abnormality" because this pattern may occur in left atrial conduction delays even without atrial enlargement

Question 18

Right ventricular hypertrophy due to pressure load (e.g. pulmonic valve stenosis or pulmonary artery hypertension) may lead to what ECG change?

Answer 18

• Relatively tall R-wave in lead V1 (R ≥ S)

* Usually with R axis deviation

Question 19

Left ventricular hypertrophy may cause what ECG changes?

Answer 19

• ST-segment depression

* T-wave inversion in leads with prominent R wave

Question 20

Acutecor pulmonaledue to pulmonary embolism may result in no ECG changes, or the following ones:

Answer 20

Sinus tachycardia most common

Other tachyarrythmias may occur			
# Slow R-wave progression	
# ST abnormalities in V1-V4 simulating acute anterior infarction

Question 21

Chroniccor pulmonaledue to obstructive lung disease may cause the following ECG changes:

Answer 21

• Small R-waves in R-to-mid precordial leads

* Low voltage complexes r/t hyperinflation of lungs

Question 22

The presence of left atrial abnormality increases likelihood of underlying left ventricular hypertrophy in which cases?

Answer 22

Cases with borderline voltage criteria

Question 23

The sensitivity of conventional voltage criteria for LVH is decreased in what 2 groups of people?

Answer 23

#Obese patients	
#Smokers

Question 24

In bundle branch blocks, the QRS vector (axis) is oriented in what direction?

Answer 24

The direction of the region where depolarization is delayed.

In plain English: TOWARD the block.So if the patient has a RBBB, the axis may be shifted to the right.

Question 25

Left bundle branch block (LBBB) is often a marker of one of four conditions (all of them not good):

Answer 25

• Coronary heart disease
• Hypertensive heart disease
• Aortic valve disease
• Cardiomyopathy

Question 26

Severe anterior wall ischemia (with or without infarction) may cause what T-wave abnormality?

Answer 26

Prominent T-wave inversion in the precordial (V1-V4) leads

Question 27

What is a pseudoinfarct pattern?

Answer 27

ST-segment elevations/depressions, tall, positive T-waves, or Q-wavesnot related to ischemic heart disease!

Question 28

ST-segment elevations may occur in 2 conditions not related to ischemia. What are they?

Answer 28

• Acute pericarditis

* Myocarditis

Question 29

What conditions other than ischemia might result in a tall, peaked T-wave?

Answer 29

• Normal variant
• Hyperkalemia
• Cerebrovascular injury
• Left ventricular volume overload

Question 30

14 points of the ECG that must be analyzed

Answer 30

• Calibration & technical features (artifact?)
• Rhythm
• Heart rate
• PR interval/AV conduction
• QRS interval
• QT/QTc interval
• Mean QRS electrical axis
• P-waves
• QRS voltages
• Precordial R-wave progression
• Abnormal Q-waves
• ST-segments
• T-waves
• U-waves