Cardiology\ Echocardiography Flashcards
On an electrocardiography (ECG), what is the unit of measurement on the x axis?
Seconds
On an electrocardiography (ECG), what is the unit of measurement on the y axis?
Millivolts
On an electrocardiography (ECG), what is the dimensions of a small box?
1 × 1 mm
On the ECG what is the dimensions of a large box?
5 × 5 mm
On the ECG what is the length of time repesented by a small box?
0.04 seconds
On the ECG what is the length of time represented by a large box?
0.2 seconds (or 0.04 seconds × 5)
On the ECG what is the name for a positive or negative deflection from the baseline?
Wave
On the ECG what is the name for a line between two waves?
Segment
On the ECG what is the name for a segment and wave combination?
Interval
Where are the precordial leads placed?
- V1: 4th intercostal space (ICS), to the right of the sternum
- V2: 4th ICS, to the left of the sternum
- V3: between V2 and V4
- V4: 5th ICS, at the mid-clavicular line
- V5: at the same level as V4 at the anterior axillary line
- V6: at the same level as V4 and V5, at the mid-axillary line
What represents atrial contraction?
P wave
What represents ventricular contraction?
QRS complex
What represents ventricular repolarization?
T wave
When reading an ECG, what components should be covered?
- Rate
- rhythm
- axis
- intervals
- hypertrophy
- evidence of myocardial infarction
How can the rate be determined?
Here are two ways:
(1) Count the number of big boxes between QRS complexes. 1 big box = 300 beats per minute (bpm); 2 = 150 bpm; 3 = 100 bpm; 4 = 75 bpm; 5 = 60 bpm; 6 = 50 bpm. It’s helpful to memorize the sequence: 300-150-100-75-60-50.
(2) Count the number of QRS complexes on the last line at the bottom of the page and multiply that number by 6 (the rhythm strip represents 10 seconds worth of electrical activity).
What does normal sinus rhythm (NSR) indicate?
NSR indicates that the electrical impulse in the heart is generated by the sinoatrial node and is following the heart’s normal circuitry (ie, from the sinoatrial node to the atrioventricular node to the bundle of His and to the Purkinje fibers)
What ECG features indicate that the patient is in sinus rhythm and that the impulse is being generated by the sinoatrial node?
- Each QRS complex is preceded by a P wave.
- The P waves are positive in I, II, and aVF
- a positive deflection indicates that an impulse is approaching a lead. I, II, and aVF are at the inferior-lateral border of the heart, so positive P waves in these leads suggest that the impulse was generated from the sinoatrial node
Sinus rhythm with the rate between 60 and 100
Normal sinus rhythm
Sinus rhythm with the rate greater than 100
Sinus tachycardia
Sinus rhythm with the rate less than 60
Sinus bradycardia
What does the electrical axis (of ECG events) represent?
The mean QRS vector =
- the summation of the amplitude and directionality of all the small vectors that make up ventricular depolarization.
- Since the left ventricle dominates ventricular depolarization, the mean QRS vector normally points inferiorly and to the patient’s left.
Which leads are used to determine axis?
- First look at the QRS complexes in leads I and aVF.
- If the QRS complex is positive in lead I and negative in aVF, look at lead II.
What is the axis?
- QRS complex is positive in lead I and aVF
Normal
What is the axis?
QRS complex is positive in lead I, negative in aVF, and positive in lead II
Normal
