RMA EKG and Electrocardiography 1 — Questions and Answers

Question 1: What does the P wave on an EKG tracing represent?

Ventricular depolarization
Atrial depolarization (Correct answer)
Ventricular repolarization
Atrial repolarization

Correct answer: Atrial depolarization

The P wave represents atrial depolarization — the electrical impulse that spreads across the atria, causing them to contract and push blood into the ventricles.

In a normal cardiac cycle on an EKG, the P wave is the first deflection and corresponds to atrial depolarization — the electrical activation of both atria. The sinoatrial (SA) node, located in the right atrium, initiates the impulse which then spreads across both atria. An absent or abnormal P wave may indicate atrial fibrillation, atrial flutter, or a junctional rhythm. Medical assistants performing EKGs must be able to identify the basic components of the cardiac cycle waveform and recognize obvious abnormalities that require the physician's immediate attention.

Question 2: How many electrodes are applied to the patient's body for a standard 12-lead EKG?

10 (Correct answer)
12
6
16

Correct answer: 10

A standard 12-lead EKG uses 10 electrodes (4 on the limbs and 6 on the chest/precordial positions) to generate 12 different views of the heart's electrical activity.

Despite being called a '12-lead' EKG, the standard recording uses only 10 electrodes: 4 limb electrodes (right arm, left arm, right leg, left leg) and 6 precordial electrodes placed on specific chest positions (V1 through V6). The 12 leads are mathematical derivations of these 10 electrode recordings and provide 12 different electrical perspectives of cardiac activity. Medical assistants must know exact electrode placement — misplacement is a leading cause of artifact and diagnostic errors. The right leg electrode serves as a ground and does not contribute to any leads.

Question 3: Where is electrode V4 placed during a 12-lead EKG?

Right sternal border, 4th intercostal space
Left sternal border, 4th intercostal space
Midclavicular line, 5th intercostal space (Correct answer)
Anterior axillary line, 5th intercostal space

Correct answer: Midclavicular line, 5th intercostal space

V4 is placed at the 5th intercostal space at the midclavicular line (the imaginary line that passes through the middle of the clavicle).

Correct precordial electrode placement is critical for accurate EKG interpretation. V1: 4th intercostal space, right sternal border. V2: 4th intercostal space, left sternal border. V3: between V2 and V4. V4: 5th intercostal space, midclavicular line. V5: anterior axillary line, same level as V4. V6: midaxillary line, same level as V4 and V5. V4 is placed near the cardiac apex. Medical assistants must palpate the ribs carefully to count intercostal spaces accurately, as misplacement can simulate or mask pathological changes.

Question 4: What EKG artifact is commonly caused by the patient's muscle movement or shivering?

AC interference (60-cycle interference)
Somatic tremor artifact (Correct answer)
Baseline wander
Lead reversal artifact

Correct answer: Somatic tremor artifact

Somatic tremor artifact appears as an irregular, rapid baseline variation on the EKG tracing caused by skeletal muscle activity such as shivering, tremors, or patient movement.

Somatic tremor (also called muscle tremor artifact) occurs when skeletal muscle electrical activity interferes with EKG recording. It appears as an erratic, jagged baseline that is irregular in both amplitude and frequency, making it difficult to identify the PQRST complex. Common causes include patient anxiety, shivering due to cold room temperature, pain, Parkinson's disease tremors, or failure to instruct the patient to remain still and relax. Medical assistants should ensure the room is warm, have the patient lie comfortably, and provide clear instructions before beginning EKG recording.

Question 5: Which EKG finding is associated with acute myocardial infarction (heart attack)?

Prolonged PR interval
ST segment elevation (Correct answer)
Shortened QT interval
Prominent U wave

Correct answer: ST segment elevation

ST segment elevation is a classic EKG finding in acute ST-elevation myocardial infarction (STEMI), indicating ischemia and injury to the myocardium.

ST segment elevation in two or more contiguous leads is the hallmark of a STEMI (ST-elevation myocardial infarction), representing complete occlusion of a coronary artery causing acute ischemic injury to the myocardium. The affected area corresponds to the leads showing elevation — for example, elevation in leads II, III, and aVF suggests an inferior MI. Medical assistants are often the first to perform the EKG on a patient presenting with chest pain and must be trained to immediately alert the physician or emergency team if ST elevation is observed, as rapid reperfusion therapy is time-critical.

Question 6: What is the normal duration of the QRS complex on a standard EKG?

0.06 to 0.10 seconds (Correct answer)
0.12 to 0.20 seconds
0.30 to 0.44 seconds
Less than 0.04 seconds

Correct answer: 0.06 to 0.10 seconds

The normal QRS complex duration is 0.06 to 0.10 seconds (60 to 100 milliseconds), representing rapid ventricular depolarization through the His-Purkinje system.

The QRS complex represents ventricular depolarization — the electrical activation of both ventricles that triggers ventricular contraction. Under normal conditions, this occurs rapidly through the His-Purkinje conduction system, producing a narrow complex (0.06–0.10 seconds). A prolonged QRS (greater than 0.12 seconds) suggests a bundle branch block (right or left BBB) or ventricular rhythm, which slows conduction. The PR interval (0.12–0.20 seconds) represents atrial depolarization and AV node conduction. Medical assistants should know normal EKG intervals to identify deviations that warrant physician review.

RMA EKG and Electrocardiography 1

What does the P wave on an EKG tracing represent?