Online Electrocardiogram 1 — Questions and Answers
Question 1: Which of the following measurements does the nurse determine is abnormal when examining an ECG strip?
- PR Interval 0.12, QRS 0.04
- PR Interval 0.18, ORS 0.06
- PR Interval 0.16, QRS 0.04
- PR Interval 0.30, QRS 0.06 (Correct answer)
Correct answer: PR Interval 0.30, QRS 0.06
A normal PR interval typically ranges from 0.12 to 0.20 seconds, and a normal QRS duration is usually 0.06 to 0.10 seconds. A PR interval of 0.30 seconds is significantly prolonged, indicating a first-degree AV block, which is an abnormal finding. The QRS duration of 0.06 seconds is within the normal range, but the prolonged PR interval makes this option abnormal.
Question 2: What information is necessary to have when interpreting an ECG strip?
- PU segment
- RS segment
- RT interval
- PR interval (Correct answer)
Correct answer: PR interval
The PR interval is a crucial measurement on an ECG strip as it represents the time taken for electrical impulse conduction from the onset of atrial depolarization (P wave) to the onset of ventricular depolarization (QRS complex). This interval provides vital information about AV nodal conduction and can indicate conditions like AV blocks or pre-excitation syndromes. The other options are not standard or clinically significant ECG intervals.
Question 3: "The QRS complex represents..." is how the nurse relates the QRS complex to the cardiac cycle.
- “atrial repolarization.”
- "ventricular depolarization.” (Correct answer)
- “atrial depolarization.”
- "ventricular repolarization.”
Correct answer: "ventricular depolarization.”
The QRS complex on an ECG tracing specifically represents ventricular depolarization, which is the electrical activation of the ventricles leading to their contraction. This is a rapid and strong electrical event, resulting in the largest deflection on the ECG. Atrial depolarization is represented by the P wave, and ventricular repolarization by the T wave.
Question 4: When examining an ECG, the nurse compares the waveform's horizontal movement across the ECG paper to
- Intensity.
- Time. (Correct answer)
- Amplitude.
- Voltage.
Correct answer: Time.
On an ECG paper, the horizontal axis represents time, with each small square typically representing 0.04 seconds and each large square (5 small squares) representing 0.20 seconds. This allows for precise measurement of intervals and durations of various waves and complexes, which is critical for rhythm analysis and identifying conduction abnormalities. The vertical axis, in contrast, represents amplitude or voltage.
Question 5: The ST segment is 3 millimeters below the isoelectric line, as the nurse notes when analyzing the ECG of a patient who is complaining of chest pain. As the nurse assesses, this is
- Not significant unless it is greater than 5mm.
- An expected finding
- A result of artifact.
- Suggestive of myocardial ischemia. (Correct answer)
Correct answer: Suggestive of myocardial ischemia.
ST segment depression, especially when 1 mm or more below the isoelectric line in multiple leads, is a significant indicator of myocardial ischemia, meaning the heart muscle is not receiving enough oxygen. A 3 mm depression is a substantial finding and, in a patient with chest pain, strongly suggests an acute coronary syndrome requiring immediate attention.
Question 6: Which of the following claims best describes the student nurse's comprehension of the ECG measurement sequence?
- “I need to count the number of small boxes present and divide that number by 300.”
- “I need to count the number of R waves during a six second period and multiply that number by 10.”
- “I need to count the number of large boxes present and divide that number by 1500.”
- “I need to select an R wave that falls on dark vertical line and number the next 6 dark vertical lines as 300, 150, 100, 75, 60, 50.” (Correct answer)
Correct answer: “I need to select an R wave that falls on dark vertical line and number the next 6 dark vertical lines as 300, 150, 100, 75, 60, 50.”
This method, often called the 'sequence method' or '300 method,' is a quick way to estimate heart rate from an ECG strip, particularly for regular rhythms. By finding an R wave on a dark line and counting the subsequent dark lines (which represent 0.20-second intervals), the corresponding rates (300, 150, 100, etc.) provide a rapid approximation of the heart rate.
Question 7: The nurse looks at an ECG strip, detects a Q wave, and determines that this waveform is
- Only visible if pathology is present. (Correct answer)
- Considered normal if less than 0.04 sec duration and less than 25% of the amplitude of the R wave.
- The first downward deflection following the P wave. (Correct answer)
Correct answer: Only visible if pathology is present.
While small, narrow Q waves can be a normal variant in some leads, the presence of a *significant* or pathological Q wave (wider than 0.04 seconds or deeper than 25% of the R wave amplitude) is a hallmark of myocardial infarction. In a clinical setting, when a nurse 'detects a Q wave,' the primary concern often shifts to assessing if it represents this critical pathology, making its visibility a strong indicator of past cardiac damage.
Online Electrocardiogram 1
Which of the following measurements does the nurse determine is abnormal when examining an ECG strip?