3.8 EKG and Cardiovascular Testing
Key Takeaways
- A standard 12-lead EKG uses 10 electrodes: 4 limb leads (RA, LA, RL, LL) and 6 precordial chest leads (V1-V6)
- Limb lead placement: RA (right arm/wrist), LA (left arm/wrist), RL (right leg/ankle), LL (left leg/ankle)
- Precordial lead placement: V1 (4th ICS right sternal border), V2 (4th ICS left sternal border), V3 (between V2 and V4), V4 (5th ICS midclavicular), V5 (anterior axillary line), V6 (midaxillary line)
- A normal EKG shows P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization)
- EKG artifacts include wandering baseline (patient movement/breathing), AC interference (60-cycle, electrical), and somatic tremor (muscle movement)
- Medical assistants perform EKGs but do NOT interpret them — only the provider interprets EKG results and makes diagnoses
EKG and Cardiovascular Testing
An electrocardiogram (EKG or ECG) is a graphic recording of the electrical activity of the heart. Medical assistants perform EKGs as part of clinical patient care, and the CCMA exam tests your knowledge of lead placement, waveform components, artifacts, and troubleshooting.
12-Lead EKG: Lead Placement
A standard 12-lead EKG uses 10 electrodes (sensors) to produce 12 different views of the heart's electrical activity:
Limb Leads (4 electrodes):
| Lead | Color | Placement |
|---|---|---|
| RA | White | Right arm (inner wrist or upper arm) |
| LA | Black | Left arm (inner wrist or upper arm) |
| RL | Green | Right leg (inner ankle or lower leg) — ground lead |
| LL | Red | Left leg (inner ankle or lower leg) |
Memory aid for limb leads: "Smoke (black-LA) over fire (red-LL)" on the left side; "Snow (white-RA) over grass (green-RL)" on the right side.
Precordial (Chest) Leads (6 electrodes):
| Lead | Placement |
|---|---|
| V1 | 4th intercostal space (ICS), RIGHT sternal border |
| V2 | 4th intercostal space (ICS), LEFT sternal border |
| V3 | Midway between V2 and V4 |
| V4 | 5th intercostal space (ICS), midclavicular line |
| V5 | Same horizontal level as V4, anterior axillary line |
| V6 | Same horizontal level as V4, midaxillary line |
How to find the 4th intercostal space:
- Locate the sternal notch (top of sternum)
- Slide fingers down to the Angle of Louis (sternal angle — raised ridge)
- The Angle of Louis is at the level of the 2nd rib
- Count down: 2nd ICS → 3rd rib → 3rd ICS → 4th rib → 4th ICS
EKG Waveforms and Intervals
| Component | What It Represents | Normal Duration |
|---|---|---|
| P wave | Atrial depolarization (atria contract) | 0.06-0.12 sec |
| PR interval | Time from atrial depolarization to ventricular depolarization | 0.12-0.20 sec |
| QRS complex | Ventricular depolarization (ventricles contract) | 0.06-0.12 sec |
| ST segment | Period between ventricular depolarization and repolarization | Isoelectric (flat) |
| T wave | Ventricular repolarization (ventricles relax/reset) | Variable |
| QT interval | Total time of ventricular depolarization and repolarization | 0.36-0.44 sec |
Normal Sinus Rhythm Characteristics:
- Regular rate: 60-100 bpm
- P wave before every QRS complex
- Consistent PR interval (0.12-0.20 sec)
- Narrow QRS complex (0.06-0.12 sec)
- Upright T wave
EKG Paper and Measurements
- The EKG records on graph paper moving at 25 mm/sec
- Horizontal axis = time (each small box = 0.04 sec; each large box = 0.20 sec)
- Vertical axis = voltage/amplitude (each small box = 0.1 mV; each large box = 0.5 mV)
- Heart rate calculation: 300 ÷ number of large boxes between two R waves = heart rate (bpm)
- Example: 4 large boxes between R waves → 300 ÷ 4 = 75 bpm
EKG Artifacts and Troubleshooting
Artifacts are unwanted marks on the EKG tracing that are NOT generated by the heart's electrical activity:
| Artifact | Appearance | Cause | Solution |
|---|---|---|---|
| Wandering baseline | Tracing drifts up and down | Patient movement, breathing, loose electrode | Have patient lie still; secure electrodes; clean skin |
| AC interference (60-cycle) | Fine, regular, fuzzy baseline | Electrical interference from nearby equipment | Unplug nearby devices; ensure proper grounding |
| Somatic tremor | Irregular, jagged baseline | Muscle tremor, shivering, tension | Relax the patient; ensure comfortable position; warm the room |
| Interrupted baseline | Tracing stops or has gaps | Loose lead wire connection; detached electrode | Check all connections; reattach electrodes |
Patient Preparation for EKG:
- Explain the procedure — painless, non-invasive
- Have the patient remove clothing from the waist up; provide gown
- Remove jewelry from wrists and ankles
- Position supine on the exam table
- Clean electrode placement sites with alcohol if oily or lotion-covered
- Shave chest hair at electrode sites if necessary (for good contact)
- Apply electrodes to flat, fleshy areas — avoid bony prominences and muscle
- Ensure the room is warm to prevent shivering (somatic artifact)
- Ask the patient to lie still, relax, and breathe normally
- Run a standard 12-lead recording
Holter Monitor
A Holter monitor provides continuous EKG recording for 24-48 hours during the patient's normal daily activities:
Indications:
- Evaluate intermittent arrhythmias (palpitations, skipped beats)
- Assess chest pain episodes
- Monitor effectiveness of cardiac medications
- Evaluate syncope (fainting)
Patient Instructions:
- Wear the monitor continuously for the prescribed period (24, 48, or 72 hours)
- Keep a patient diary documenting:
- Activities (exercise, eating, sleeping)
- Symptoms (chest pain, dizziness, palpitations)
- Times of symptoms and activities
- Do NOT get the monitor wet (no bathing/swimming)
- Avoid electric blankets, magnets, and metal detectors
- Avoid pressing on electrodes
- Return the monitor at the scheduled time
Common Cardiac Rhythms (Recognition Only)
| Rhythm | Description | Key Features |
|---|---|---|
| Normal sinus rhythm | Normal heart rhythm | Regular, 60-100 bpm, P before QRS |
| Sinus tachycardia | Fast normal rhythm | Regular, >100 bpm, P before QRS |
| Sinus bradycardia | Slow normal rhythm | Regular, <60 bpm, P before QRS |
| Atrial fibrillation | Irregular atrial activity | Irregular rhythm, no clear P waves, wavy baseline |
| Atrial flutter | Rapid atrial activity | Sawtooth pattern, regular or irregular ventricular response |
| Premature ventricular contraction (PVC) | Early ventricular beat | Wide, bizarre QRS without preceding P wave |
| Ventricular tachycardia | Rapid ventricular rhythm | Wide QRS, >100 bpm, medical emergency |
| Ventricular fibrillation | Chaotic ventricular activity | No identifiable waves, cardiac arrest, requires immediate defibrillation |
Remember: Medical assistants perform EKGs but do NOT interpret rhythms or diagnose conditions. Only the provider interprets the EKG and determines the clinical significance.
Where is the V1 precordial lead placed?
The QRS complex on an EKG represents:
A fine, regular, fuzzy pattern on the EKG baseline most likely indicates:
The memory aid for EKG limb lead placement color coding is "Smoke over fire, snow over grass." Where does the BLACK lead go?