Download Chapter06_Detailed_Answers

Chapter 6
Detailed Answers to Assess Your Understanding
1. b:
To analyze the atrial activity of an ECG you assess the P waves.
2. b:
The amplitude of the P wave normally does not exceed 2.5 mm high. Its duration is
normally 0.06 to 0.10 seconds.
3. d:
An upright, round P wave (in lead II) that precedes each QRS complex indicates that the
electrical impulse originated in the SA node and was carried through the atria in a normal
manner.
4. d:
The characteristic considered normal (in lead II) is a rounded and upright P wave.
5. c:
With ECG waveforms, the lead you select affects your ability to assess their morphology.
As such, the answer for this question is the P waves are best evaluated by choosing the
appropriate lead.
6. b:
With increased left atrial pressure and left atrial enlargement, the P wave is normally
notched or wide.
7. a:
Enlarged or damaged atria produce P waves that look different than sinus P waves. Tall
and symmetrically peaked P waves suggest increased right atrial pressure and right atrial
enlargement. Notched or wide (prolonged) P waves indicate increased left atrial pressure and
left atrial enlargement.
8. a:
An impulse that arises closer to the SA node has the same appearance as a normal P
waves. In contrast, if the impulse arises from the lower-right atrium, near the AV node or in the
left atrium, depolarization occurs in a retrograde direction resulting in the P’ wave being
inverted in lead II.
9. c:
Early beats that arise from the atria may have P’ waves which are buried in the T wave
of the preceding beat. This can cause the T wave to appear notched or different than other T
waves in the tracing.
10. b:
With tachycardia that arises from the atria, the P’ wave looks different than P waves
that arise from the SA node.
11. a:
An atrial pacemaker site that changes from location to location has P waves that
continually change in appearance.
12. a:
When the atria fire faster than 350 beats per minute, the P waves are indiscernible;
instead, there is a chaotic-looking baseline.
13. b:
Dysrhythmias that arise from AV junctional tissue have inverted P’ waves.
14. d:
With ventricular dysrhythmias, the P’ waves are absent.
15. c:
AV heart block has more P waves than QRS complexes.
16. d:
the patient’s dysrhythmia originated from the atria.
17. d:
The firing rate of the F waves is 144 beats per minute.