NCMA EKG and Cardiovascular Procedures 1 — Questions and Answers

Question 1: How many electrodes are placed on the patient for a standard 12-lead EKG?

10 electrodes (4 limb + 6 precordial) (Correct answer)
12 electrodes (one per lead)
6 electrodes (one per precordial lead only)
8 electrodes (4 limb + 4 chest)

Correct answer: 10 electrodes (4 limb + 6 precordial)

A 12-lead EKG uses 10 electrodes — 4 limb electrodes (RA, LA, RL, LL) and 6 precordial (chest) electrodes (V1–V6). These 10 electrodes mathematically generate 12 distinct views of the heart's electrical activity.

The 12-lead EKG uses 10 electrodes to produce 12 views (leads): Limb leads (frontal plane): Lead I (LA-RA), Lead II (LL-RA), Lead III (LL-LA), aVR, aVL, aVF — derived from 4 limb electrodes; Precordial/chest leads (horizontal plane): V1–V6 — 6 individual chest electrodes. The right leg electrode serves as the ground/reference. Total = 10 electrodes producing 12 leads. Medical assistants must correctly place all 10 electrodes for diagnostic accuracy. Misplacement (especially limb lead reversal or wrong precordial position) produces diagnostic errors. Proper skin preparation, correct electrode placement, and artifact-free recording are essential MA competencies.

Question 2: Where is the V1 precordial electrode placed for a standard 12-lead EKG?

Fourth intercostal space, left sternal border
Fourth intercostal space, right sternal border (Correct answer)
Fifth intercostal space, midclavicular line
Second intercostal space, right sternal border

Correct answer: Fourth intercostal space, right sternal border

V1 is placed at the 4th intercostal space on the RIGHT sternal border. V2 mirrors it on the LEFT sternal border. Accurate placement requires locating the sternal angle (angle of Louis) and counting intercostal spaces.

Precordial lead placement: V1 — 4th ICS, right sternal border; V2 — 4th ICS, left sternal border; V3 — between V2 and V4; V4 — 5th ICS, left midclavicular line; V5 — anterior axillary line, same horizontal level as V4; V6 — midaxillary line, same level as V4 and V5. How to locate the 4th ICS: palpate the suprasternal notch, slide finger down to the sternal angle (angle of Louis/manubriosternal junction, at the level of the 2nd rib), then count down to the 4th intercostal space. Proper precordial placement is critical — misplaced leads cause poor R-wave progression and can suggest anterior MI erroneously.

Question 3: What does the P wave represent on an EKG tracing?

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

Correct answer: Atrial depolarization

The P wave represents atrial depolarization — the electrical activation spreading across the atria that triggers atrial contraction. It precedes the QRS complex in normal sinus rhythm.

Normal EKG waveform components: P wave — atrial depolarization (atrial activation); Normal: <0.12 sec (3 small squares), upright in II; PR interval — time from atrial activation to ventricular activation (AV node delay); Normal: 0.12–0.20 sec (3–5 small squares); QRS complex — ventricular depolarization; Normal: <0.12 sec; ST segment — early ventricular repolarization; normally at baseline; T wave — ventricular repolarization (recovery); U wave — sometimes seen, represents Purkinje fiber repolarization; QT interval — total ventricular electrical activity. Atrial repolarization occurs within the QRS complex and is not visible on surface EKG.

Question 4: A patient's EKG shows a heart rate of 110 bpm with regular rhythm and normal P waves before each QRS. This rhythm is classified as:

Atrial fibrillation
Sinus bradycardia
Sinus tachycardia (Correct answer)
Ventricular tachycardia

Correct answer: Sinus tachycardia

Sinus tachycardia is defined as a regular rhythm originating in the SA node (normal P waves before each QRS, consistent PR interval) with a rate exceeding 100 bpm. At 110 bpm with the described characteristics, this is sinus tachycardia.

Rhythm identification requires assessment of: rate, regularity, P waves (present, shape, one before each QRS), PR interval, QRS width. Sinus rhythms: Sinus rhythm — 60–100 bpm, regular, normal P waves; Sinus tachycardia — >100 bpm, regular, normal P waves; Sinus bradycardia — <60 bpm, regular, normal P waves. Common causes of sinus tachycardia: fever, pain, anxiety, dehydration, anemia, hyperthyroidism, stimulants. Medical assistants should recognize sinus tachycardia, bradycardia, atrial fibrillation (absent P waves, irregularly irregular), and ventricular fibrillation (chaotic, no recognizable waveforms) to assist with appropriate physician notification.

Question 5: What is the primary reason for skin preparation before placing EKG electrodes?

To mark the correct electrode placement sites on the skin
To reduce skin resistance and ensure good electrical contact, reducing artifact (Correct answer)
To disinfect the skin before the sterile electrode is applied
To prevent the patient from feeling pain when electrodes are removed

Correct answer: To reduce skin resistance and ensure good electrical contact, reducing artifact

Skin has natural oils, dead cells, and impedance (resistance) that interfere with EKG signal quality. Proper skin preparation (light abrasion, cleansing with alcohol or dry cloth) reduces this resistance and improves electrode contact, minimizing artifact.

EKG skin preparation steps: (1) Dry the skin if moist/diaphoretic; (2) Wipe electrode sites with an alcohol prep pad and allow to dry completely (wet alcohol increases impedance); (3) For oily or hairy skin: gently abrade with a dry gauze or mild abrasive pad to remove dead skin cells; (4) For excessive hair: clip if necessary (shaving not required unless absolutely necessary for contact); (5) Apply electrodes firmly, pressing down all edges to ensure good adhesion. Poor preparation causes: 60-cycle interference (AC artifact), wandering baseline, muscle artifact. Common artifacts: wandering baseline (breathing, loose electrode), somatic tremor (patient movement/shivering), AC interference (electrical equipment). The medical assistant should ensure the tracing is free of artifact before the physician reviews.

Question 6: What does a prolonged QT interval on an EKG indicate, and why is it clinically significant?

Delayed atrial conduction; can cause atrial flutter
Prolonged ventricular repolarization; increases risk of life-threatening ventricular arrhythmias such as Torsades de Pointes (Correct answer)
Delayed AV node conduction; indicates first-degree heart block
Rapid ventricular repolarization; normal variant in athletes

Correct answer: Prolonged ventricular repolarization; increases risk of life-threatening ventricular arrhythmias such as Torsades de Pointes

The QT interval represents total ventricular electrical activity (depolarization + repolarization). Prolonged QT indicates delayed ventricular repolarization and predisposes patients to potentially fatal ventricular arrhythmias, particularly Torsades de Pointes (a polymorphic ventricular tachycardia).

QT interval: measured from start of Q wave to end of T wave; represents ventricular depolarization + repolarization time. Corrected QT (QTc) adjusts for heart rate. Normal QTc: men <440 ms; women <460 ms. Prolonged QTc: >500 ms significantly increases arrhythmia risk. Causes of prolonged QT: congenital long QT syndrome, medications (quinolone antibiotics, antipsychotics, antihistamines, antiarrhythmics), electrolyte imbalances (hypokalemia, hypomagnesemia, hypocalcemia), bradycardia, hypothyroidism. Torsades de Pointes (TdP): 'twisting of the points,' polymorphic VT that can degenerate into ventricular fibrillation and sudden cardiac death. Medical assistants must flag prolonged QTc for physician review.

NCMA EKG and Cardiovascular Procedures 1

How many electrodes are placed on the patient for a standard 12-lead EKG?