Guide — Cardiac
EKG Basics — Rate, Rhythm & Telemetry Reading
This guide is for nurses starting out with telemetry monitoring. It covers what you need to read a rhythm strip at the bedside — how to calculate rate, how to classify rhythm regularity, how to assess P waves, and how to recognize the rhythms you will see most often in clinical practice.
10 min read · Telemetry & Cardiac Monitoring
Educational use only. EKG interpretation in clinical settings requires licensed supervision and must follow institutional protocols. Always correlate strip findings with patient assessment. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
EKG Paper Basics
Standard EKG paper runs at 25 mm/second. Each small box = 0.04 seconds; each large box (5 small boxes) = 0.20 seconds.
- Horizontal axis: time (seconds)
- Vertical axis: voltage (millivolts) — 1 large box = 0.5 mV at standard calibration
- A complete cardiac cycle (P–QRS–T) occupies roughly 3–5 large boxes at a normal rate
Step 1 — Rate
Normal heart rate: 60–100 bpm. Bradycardia < 60; tachycardia > 100.
Two methods to calculate rate:
- 300 method (regular rhythms): Count the large boxes between two consecutive R waves. Divide 300 by that count. E.g., 4 large boxes = 300 ÷ 4 = 75 bpm.
- 6-second strip method (irregular rhythms): Count the QRS complexes in a 6-second strip (30 large boxes) and multiply by 10.
Step 2 — Rhythm Regularity
Classify the rhythm by comparing R-to-R intervals across the strip. This one assessment eliminates many diagnoses.
- Regular: R-to-R intervals are consistent throughout. Most sinus rhythms and tachycardias are regular.
- Regularly irregular: A repeating pattern of irregularity (e.g., PACs in a fixed pattern, Wenckebach grouping).
- Irregularly irregular: No discernible pattern — the classic finding in atrial fibrillation.
Tip: place a card at the edge of the strip and mark several R wave peaks. Walk the card across to check for consistent spacing.
Step 3 — P Waves
P waves represent atrial depolarization from the SA node. Two bedside questions answer most rhythm questions:
- Is there a P before every QRS? — Confirms the beat is coming from a supraventricular source
- Is there a QRS after every P? — Confirms conduction is reaching the ventricles
- Normal P wave in lead II: upright, rounded, < 0.12 s wide, < 2.5 mm tall
- Absent P waves + irregularly irregular rhythm = atrial fibrillation until proven otherwise
- Inverted P waves in lead II = junctional rhythm or ectopic atrial source
Steps 4–5 — PR Interval & QRS Width
| Parameter | Normal | Abnormal Finding |
|---|---|---|
| PR interval | 0.12–0.20 sec (3–5 small boxes) | > 0.20 s = delayed AV conduction; progressive lengthening then dropped QRS = Wenckebach |
| QRS width | < 0.12 sec (< 3 small boxes) | ≥ 0.12 s = wide QRS — bundle branch block, ventricular origin, or hyperkalemia |
Common Rhythms at a Glance
These are the rhythms you will encounter most frequently on telemetry. Learn to recognize each by its rate, rhythm regularity, and P wave pattern.
| Rhythm | Rate | Regularity | P Waves | Key Finding |
|---|---|---|---|---|
| Normal Sinus Rhythm | 60–100 | Regular | Yes — upright, uniform | All parameters within normal limits |
| Sinus Bradycardia | < 60 | Regular | Yes — upright | Rate below 60; assess for symptoms (dizziness, hypotension) |
| Sinus Tachycardia | 100–150 | Regular | Yes — may be hard to see at fast rates | Rate above 100; find and treat the cause (fever, pain, hypovolemia) |
| Atrial Fibrillation | Variable | Irregularly irregular | Absent — fibrillatory baseline | No true P waves; chaotic atrial activity; classic irregularly irregular pattern |
| Ventricular Tachycardia | > 100 | Regular | May be absent or dissociated | Wide QRS (≥ 0.12 s) at fast rate — treat as dangerous until proven otherwise |
| Ventricular Fibrillation | None | Chaotic | None | No organized QRS; chaotic waveforms — immediately life-threatening; call code |
Five-Step Bedside Method
| Step | Ask | Normal Answer |
|---|---|---|
| 1 | What is the rate? | 60–100 bpm |
| 2 | Is the rhythm regular? | Regular R-to-R intervals |
| 3 | Are P waves present and uniform? | Yes — upright in lead II, P before every QRS |
| 4 | Is the PR interval normal? | 0.12–0.20 sec |
| 5 | Is the QRS narrow? | < 0.12 sec (narrow) |
If a patient's rhythm looks abnormal, work through these five steps systematically before calling for help — it frames the problem and helps you give a clear report.
When to Escalate Immediately
The following telemetry findings require immediate provider notification regardless of whether the patient currently appears symptomatic:
- Ventricular fibrillation (VF) — no pulse, call code immediately
- Pulseless ventricular tachycardia — treat as VF; call code
- Asystole — confirm in two leads; call code
- Symptomatic bradycardia — rate < 50 with hypotension, syncope, or altered mentation
- Wide QRS tachycardia — fast rate + wide QRS = VT until proven otherwise; notify provider
- New third-degree (complete) AV block — P waves with no relationship to QRS complexes
Ready for the Next Level?
Practice These Rhythms
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with American Heart Association (AHA) · American College of Cardiology (ACC) · AHA ACLS Guidelines. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →