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ECG: From Basics to Advanced - A Complete Guide

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PART 1 - FUNDAMENTALS

What Is an ECG?

• Medical Physiology, p. 731

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The Cardiac Conduction System

• Miller's Anesthesia 10e, p. 1364

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The Cardiac Cycle and ECG Correlation

• P wave - Atrial depolarization; onset of atrial systole coincides with SA node firing
• PR interval - Conduction delay through AV node; onset of P wave to start of QRS
• QRS complex - Ventricular depolarization; mitral valve closes at end of R wave
• ST segment - Plateau phase of ventricular action potential (isoelectric in normal)
• T wave - Ventricular repolarization
• QT interval - Total ventricular depolarization + repolarization time; shortens as heart rate increases

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PART 2 - ECG PAPER AND LEADS

ECG Paper Calibration

• Horizontal axis (time): 0.04 sec per small box (1 mm); 0.2 sec per large box (5 mm)
• Vertical axis (voltage): 0.1 mV per mm; standard calibration = 1 mV = 10 mm tall
• 5 large boxes = 1.0 second

The 12-Lead System

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PART 3 - SYSTEMATIC ECG INTERPRETATION

Step 1 - Rate

• Normal: 60-100 bpm
• Bradycardia: <60 bpm
• Tachycardia: >100 bpm

Step 2 - Rhythm

• Rate 60-100 bpm
• Regular R-R intervals
• Upright P waves in leads I, II, aVF
• Constant PR interval (0.12-0.20 sec)
• Each P followed by a QRS

Step 3 - Intervals and Durations

Step 4 - Electrical Axis

Step 5 - P Wave Morphology

• P pulmonale: Tall, peaked P waves >2.5 mm in lead II - right atrial enlargement
• P mitrale: Broad, notched P wave >0.12 sec in lead II with biphasic P in V1 - left atrial enlargement

Step 6 - QRS Morphology

• Width >0.04 sec (1 small box) OR
• Depth >1/4 of following R wave
• Indicate prior myocardial infarction

Step 7 - ST Segment and T Wave

• ST elevation (>1 mm limb leads, >2 mm precordial leads): STEMI, pericarditis, Brugada, early repolarization
• ST depression: Subendocardial ischemia, digoxin effect, LVH strain
• T wave inversion: Ischemia, PE (right-sided), RBBB, LVH, normal in aVR and V1

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PART 4 - BUNDLE BRANCH BLOCKS

Right Bundle Branch Block (RBBB)

• QRS ≥ 0.12 sec
• RSR' ("M" or "rabbit ears") pattern in V1 (rSR')
• Wide, slurred S wave in leads I and V6
• T wave inversion in V1-V3 (appropriate discordance)

Left Bundle Branch Block (LBBB)

• QRS ≥ 0.12 sec
• Broad, notched R wave in V5, V6, I, aVL (no S wave)
• Deep, wide QS complex in V1
• No septal Q waves in lateral leads
• Discordant ST changes (opposite to QRS deflection)

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PART 5 - ARRHYTHMIAS

Bradyarrhythmias

• Rate <60 bpm, normal P waves, regular rhythm
• Causes: Athletes, vagal tone, hypothyroidism, beta-blockers, sick sinus syndrome

• Goldman-Cecil Medicine, p. 1764

Supraventricular Tachyarrhythmias

• Irregularly irregular rhythm
• No visible P waves - replaced by chaotic fibrillatory baseline (best seen in V1)
• Narrow QRS (unless aberrant conduction)
• Rate: Usually 100-170 bpm (ventricular response)

• Regular "sawtooth" flutter waves at 300 bpm (F waves)
• Typically 2:1 AV block giving ventricular rate of 150 bpm
• Flutter waves best seen in inferior leads (II, III, aVF) and V1
• Unlike AF, flutter waves are organized and regular

• Rate 150-250 bpm, regular
• Narrow QRS
• P waves buried in or just after QRS (retrograde P waves)
• Responds to vagal maneuvers and adenosine

• May be narrow (orthodromic) or wide (antidromic)
• Short PR (<0.12 sec) + delta wave on baseline ECG = WPW pattern
• During tachycardia, typically narrow QRS (conduction goes normal route down His and back via accessory pathway)

• AV dissociation = VT (P waves march through at own rate, independent of QRS)
• Fusion beats = VT (hybrid complexes where normal conduction fuses with ventricular focus)
• Capture beats = VT
• Concordance in precordial leads (all positive or all negative) = VT

Ventricular Arrhythmias

• Wide (>0.12 sec), bizarre QRS
• No preceding P wave
• Followed by compensatory pause
• Isolated PVCs in structurally normal hearts are generally benign

• ≥3 consecutive PVCs at rate >100 bpm
• Wide QRS (>0.12 sec), regular
• AV dissociation, fusion beats, capture beats confirm VT
• Monomorphic VT: all QRS complexes look alike - often from a fixed scar (post-MI)
• Polymorphic VT: changing QRS morphology

• Chaotic, disorganized electrical activity
• No identifiable QRS complexes
• No cardiac output - immediately fatal without defibrillation

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PART 6 - ISCHEMIA AND INFARCTION

The Progression of ECG Changes in MI

STEMI Localization by Leads

Special STEMI Patterns

• Rosen's Emergency Medicine, p. 1004

• Prominent tall T waves with J-point depression (ST depression) in precordial leads
• ST elevation in aVR
• Indicates proximal LAD occlusion; must be treated as STEMI

• Deep symmetric T-wave inversions or biphasic T waves in V2-V3
• Occurs during pain-free period
• Indicates critical proximal LAD stenosis - do NOT stress test; needs urgent cath

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PART 7 - ADVANCED PATTERNS

LVH (Left Ventricular Hypertrophy)

• Sokolow-Lyon: S in V1 + R in V5 or V6 ≥ 35 mm (sensitivity low ~40-60% in middle-age adults)
• Cornell: R in aVL + S in V3 > 28 mm (men) or >20 mm (women)
• Associated with ST-T changes in lateral leads ("strain pattern")

RVH (Right Ventricular Hypertrophy)

• Right axis deviation
• R > S in V1 (dominant R in V1)
• Deep S waves in V5-V6
• ST depression and T inversion in V1-V3

Pericarditis

• Diffuse ST elevation in multiple leads (not restricted to one territory)
• ST elevation is concave (saddle-shaped) upward
• PR depression (a key distinguishing feature from STEMI)
• No reciprocal ST depression (unlike STEMI)
• T wave inversion occurs after ST returns to baseline

Pulmonary Embolism (PE) - S1Q3T3 pattern

• S wave in lead I
• Q wave in lead III
• T wave inversion in lead III
• Also: sinus tachycardia (most common), new RBBB, right heart strain pattern (T inversion V1-V4), right axis deviation
• S1Q3T3 is specific but not sensitive - present in <20% of PE cases

Hyperkalemia - Progressive ECG Changes

1. Peaked (tall, narrow) T waves - earliest sign
2. Prolonged PR interval
3. Widened QRS (loss of P waves)
4. Sine wave pattern (merged QRS and T)
5. Ventricular fibrillation / asystole

Hypokalemia

• Flattened T waves
• Prominent U waves (after T wave, best in V2-V3)
• Prolonged QU interval
• ST depression

Brugada Syndrome

• Type 1 (diagnostic): Coved-type (downsloping) ST elevation ≥2 mm in ≥1 of V1-V2, followed by negative T wave
• Can cause sudden cardiac death from polymorphic VT/VF
• ECG may be dynamic (appears and disappears)

Long QT Syndrome

• Congenital (mutations in ion channel genes) or acquired (drugs, electrolyte disturbances)
• QTc > 0.44 sec (men) or >0.46 sec (women)
• Risk of Torsades de Pointes - polymorphic VT with "twisting" QRS around the isoelectric line
• Acquired causes: hypokalemia, hypomagnesemia, antiarrhythmics (class Ia, III), antipsychotics, azole antifungals, fluoroquinolones

Wolff-Parkinson-White (WPW) Syndrome

• Accessory pathway (Bundle of Kent) bypasses AV node
• ECG features: short PR interval (<0.12 sec) + delta wave (slurred upstroke of QRS) + wide QRS
• Risk: AF with rapid accessory pathway conduction can lead to VF
• Never give AV nodal blocking agents (adenosine, verapamil, digoxin) in AF with WPW - can accelerate conduction down accessory pathway

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PART 8 - STEP-BY-STEP SYSTEMATIC APPROACH (Summary Checklist)

1. RATE         - Calculate bpm (regular: 300/large boxes; irregular: count x6)
2. RHYTHM       - Regular or irregular? P before every QRS?
3. P WAVES      - Present? Morphology? Axis (upright in II)?
4. PR INTERVAL  - 0.12-0.20 sec? Short (preexcitation)? Long (AV block)?
5. QRS          - Width <0.12 sec? Morphology? Pathologic Q waves?
6. AXIS         - Check leads I and aVF; Normal / LAD / RAD?
7. ST SEGMENT   - Elevation or depression? Which leads?
8. T WAVES      - Upright? Inverted? Hyperacute? Location?
9. QT INTERVAL  - Calculate QTc; prolonged?
10. OVERALL     - Clinical context + synthesize findings

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Quick Reference: Key Normal Values

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NCLEX-RN Complete Preparation Guide - From Scratch to Pass

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SECTION 1 - UNDERSTAND THE EXAM FIRST

What the NCLEX-RN Actually Is

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Exam Format (2026 - Current)

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2026 NCLEX-RN Content Blueprint (Client Needs Categories)

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NGN Question Types You'll See

1. Recognize Cues - what findings matter?
2. Analyze Cues - what do they mean?
3. Prioritize Hypotheses - what is most likely/urgent?
4. Generate Solutions - what can be done?
5. Take Actions - what do I do first?
6. Evaluate Outcomes - did the intervention work?

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SECTION 2 - HIGH-YIELD CONTENT MASTERY

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#1 - PRIORITIZATION FRAMEWORKS (most tested concept)

• Airway obstruction > respiratory failure > hemorrhage > everything else

• Hunger/pain/breathing > safety > belonging > esteem > self-actualization

• Newly deteriorating (not baseline)
• Has an airway/breathing/circulation threat
• Is postoperative (higher risk for complications)
• Has an unexpected/abnormal finding (vs. expected)

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#2 - DELEGATION RULES

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#3 - INFECTION CONTROL & ISOLATION PRECAUTIONS

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#4 - PHARMACOLOGY ESSENTIALS

Anticoagulants

Cardiac Drugs

Pain Management

• Opioids: Monitor respirations (hold if RR <12), have naloxone (Narcan) available
• NSAIDs: Avoid with renal impairment, peptic ulcers, anticoagulant use

Psychiatric Medications

Electrolyte-Altering Drugs

• Loop diuretics (furosemide): cause hypokalemia, hyponatremia, hypomagnesemia
• Potassium-sparing diuretics (spironolactone): cause hyperkalemia
• Corticosteroids: cause hyperglycemia, hypokalemia, Na/fluid retention, immunosuppression

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#5 - CRITICAL LAB VALUES (understand meaning, not numbers)

• Respiratory Opposite: pH up + CO2 down = respiratory alkalosis; pH down + CO2 up = respiratory acidosis
• Metabolic Equal: pH up + HCO3 up = metabolic alkalosis; pH down + HCO3 down = metabolic acidosis
• Normal values: pH 7.35-7.45, PaCO2 35-45, HCO3 22-26

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#6 - PRIORITY CONDITIONS BY BODY SYSTEM

Cardiovascular

• Chest pain - first priority is always 12-lead ECG and oxygen; STEMI = activate cath lab
• Heart failure - assess lung sounds, daily weights (1 kg = ~1L fluid); position HOB 30-45°
• Hypertensive crisis - SBP >180 + end organ damage = emergency; gradual reduction (not too fast)

Respiratory

• Airway obstruction - #1 priority always; jaw thrust in trauma
• Tension pneumothorax - tracheal deviation, absent breath sounds, hypotension = needle decompression
• PE - sudden dyspnea, tachycardia, pleuritic chest pain; anticoagulate immediately
• COPD - low-flow O2 (target SpO2 88-92%); high O2 removes hypoxic drive

Neurological

• Stroke (FAST) - Face drooping, Arm weakness, Speech difficulty, Time to call 911
• Ischemic stroke: tPA within 4.5 hours (check contraindications)
• Hemorrhagic stroke: NO tPA, control BP
• Increased ICP - HOB at 30°, avoid hip flexion, avoid Valsalva, hyperventilate if herniation imminent

OB/Maternity (heavily tested)

Pediatrics

• 2 months: social smile
• 4 months: head control, laughs
• 6 months: sits with support, rolls
• 9 months: sits alone, says mama/dada
• 12 months: walks with support, 1-3 words
• 18 months: walks well, 10-word vocabulary
• 2 years: 2-word phrases, runs
• 3 years: 3-word sentences, rides tricycle
• 5 years: ties shoes, 5-6 word sentences

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#7 - MENTAL HEALTH / PSYCHIATRIC NURSING

• ALWAYS acknowledge feelings first ("You seem upset. Tell me more about what you're feeling.")
• AVOID: false reassurance ("Everything will be fine"), giving advice, yes/no questions, changing the subject
• AVOID: "Why" questions ("Why did you do that?") - implies judgment

• Direct questions do NOT plant the idea - always ask directly about suicidal ideation
• Highest risk: specific plan + lethal means + timeline
• Nursing priority: safety first - remove all sharp objects, cords, shoelaces; 1:1 monitoring

• Denial: refuses to accept reality
• Projection: attributing own feelings to others
• Rationalization: making excuses
• Regression: reverting to earlier behavior under stress
• Displacement: redirecting feelings to safer target

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#8 - POST-OPERATIVE CARE PRIORITIES

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SECTION 3 - TEST-TAKING STRATEGIES

The NCLEX Thinking Process

1. What is the question actually asking? (Reread the last sentence of the stem)
2. What are the key clinical data? (Vitals, symptoms, timing, history)
3. Who is the sickest/most unstable?
4. What would a safe, reasonable nurse do FIRST?

Elimination Strategies

• Eliminate options that are harmful - never choose an action that could hurt the patient
• Eliminate options that delay care - "call the doctor and wait" is rarely the first action
• Eliminate options that pass the buck - "refer to another nurse" is rarely correct
• Prefer assessment over intervention (when the patient status is unclear)
• Prefer independent nursing actions over calling the physician (for initial steps)

When You See "Which patient do you see FIRST?"

• Airway/breathing compromised
• Hemodynamically unstable
• Newly worsening (not at their baseline)
• Post-procedure/post-op within first hours
• Presenting with unexpected or abnormal findings

When You See "What do you do FIRST?"

1. Assess the problem fully (if unknown status)
2. Ensure patient safety (position, airway)
3. Independent nursing action
4. Notify physician
5. Document

Reading NGN Case Studies

1. Read the chief complaint and initial vitals first
2. Identify what's abnormal/unexpected
3. Apply the 6 clinical judgment steps
4. For each subsequent question, note how the patient's condition evolves
5. Remember: partial credit means attempting all answers thoughtfully is better than leaving any blank

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SECTION 4 - STUDY PLAN (8-Week Schedule)

Before You Start

• Get your ATT (Authorization to Test) letter from your state board
• Choose a question bank: UWorld (gold standard), Kaplan, NCLEX Bootcamp, or Saunders
• Get a content review book (Saunders NCLEX-RN or Lippincott Q&A)
• Schedule 4-6 hours of focused study daily

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8-Week Study Plan

• 15 questions BEFORE studying content (reveals gaps)
• 45-60 min content review on that topic
• 35 more questions on the same topic
• 20 min reviewing ALL rationales (right AND wrong answers)

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Study Method: Question-First Learning

1. Do 10-15 questions on Topic X
2. Note what you got wrong AND what you guessed on
3. Study only the concepts you're unsure of
4. Do 20 more questions
5. Review all rationales

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SECTION 5 - EXAM DAY CHECKLIST

• No new studying (sleep is more valuable)
• Pack: valid ID, ATT confirmation, snacks, water
• Know the testing center location and parking

• Light meal (complex carbs + protein)
• Arrive 30 min early
• No phone in testing room

• Read every word of the stem carefully (what type of patient? what phase of care?)
• Trust your first instinct if you genuinely know it
• Flag uncertain questions and come back
• If you see 85 questions and the exam stops - you could have passed or failed; there is no way to tell
• If the exam runs long (100+), stay calm - it means the algorithm still needs data and is NOT a sign of failure

• Every question is independent - forget the last question
• Think "What would a safe nurse do?" not "What would I do?"
• Avoid the "analysis paralysis" trap: if 2 answers both seem correct, ask which one addresses the PRIMARY concern

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SECTION 6 - FREE AND PAID RESOURCES

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QUICK REFERENCE CARD - Most Tested NCLEX Facts

PRIORITY ORDER:    Airway > Breathing > Circulation > Safety
DELEGATION:        Assessment = RN only; Stable ADLs = UAP
ISOLATION:         Airborne = N95 + negative pressure room
PPE ON:            Gown → Mask → Goggles → Gloves
PPE OFF:           Gloves → Goggles → Gown → Mask
C. DIFF:           Soap & water (not hand sanitizer)
DIGOXIN HOLD:      HR < 60
BETA BLOCKER:      Never stop abruptly
HEPARIN ANTIDOTE:  Protamine sulfate
WARFARIN ANTIDOTE: Vitamin K (Phytonadione)
LITHIUM TOXICITY:  Level > 1.5 mEq/L
CLOZAPINE:         Weekly CBC (agranulocytosis)
MAOI + TYRAMINE:   Hypertensive crisis
O2 IN COPD:        88-92% SpO2 target
STROKE + tPA:      Within 4.5 hours (ischemic only)
PREECLAMPSIA:      Mag sulfate; antidote = calcium gluconate
PLACENTA PREVIA:   NO vaginal exams
EPIGLOTTITIS:      Don't look in throat; protect airway
MALIGNANT HYPERT:  Dantrolene immediately

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NCLEX-RN Practice Questions: Delegation & Priority Setting

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PART A - DELEGATION (Who Does What?)

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• B - Scheduled oral meds to stable patients = within LPN scope
• D - Reinforcing (not initiating) existing teaching = LPN scope; initial teaching belongs to RN
• E - Monitoring and reporting drain output on a stable patient = LPN scope
• A - IV push medications are not in LPN scope in most states
• C - Initial assessment is an RN-only responsibility
• F - Titrating IV drips requires clinical judgment; RN only

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PART B - PRIORITY SETTING (Which Patient First?)

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1. Patient with HIV/AIDS, CD4 count 85, temperature 102.4°F (39.1°C), new cough
2. Patient with stable CHF, SpO2 94% on 2L O2 at their usual baseline
3. Patient with schizophrenia expressing active suicidal ideation with a specific plan
4. Patient post-laparoscopic appendectomy day 1, pain 4/10, tolerating diet
5. Patient in a new cast with pain 8/10, toes cool and pale

• 5 first - Cool, pale toes in a new cast = possible compartment syndrome, limb-threatening emergency requiring immediate vascular assessment
• 3 second - Active suicidal ideation with a plan = immediate safety risk, 1:1 precautions needed now
• 1 third - Fever in an immunocompromised patient (CD4 <200 = AIDS) with new cough = possible opportunistic infection / sepsis risk; needs rapid assessment
• 2 fourth - Stable CHF at baseline; needs attention but not urgent
• 4 last - Expected post-op day 1 findings; stable and predictable

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PART C - COMBINED DELEGATION + PRIORITY (NGN-Style Scenarios)

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• B - Hold digoxin: HR is 58 (below 60 = hold), plus hypokalemia increases toxicity risk
• D - Furosemide (loop diuretic) will further lower potassium - hold and clarify
• F - Cardiac monitoring is prudent given hypokalemia + digoxin risk for arrhythmia
• A - Incorrect: never give digoxin when HR <60
• C - Incorrect: furosemide worsens hypokalemia
• E - SpO2 is 96% and patient is not in distress; O2 not indicated

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PART D - QUICK-FIRE SCENARIOS (10 Questions, Rapid Review)

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• A. Pain 8/10 post-op day 1 (stable, VS normal)
• B. Chest pain 6/10, diaphoretic, HR 110
• C. Headache 5/10, BP 138/86, stable
• D. Nausea after chemotherapy

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• A. Patient 2 hours post-op from knee replacement
• B. Patient with pneumonia who is afebrile x24 hrs, SpO2 96% on RA, tolerating PO
• C. Patient with new insulin regimen who hasn't completed diabetes teaching
• D. Patient awaiting cardiac catheterization tomorrow

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• A. Post-op patient with fever 38.8°C on day 1
• B. Patient with COPD at their baseline, requesting water
• C. Patient reporting sudden vision loss in one eye
• D. Patient on a heparin drip with aPTT result just returned

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• A. A patient 30 minutes post-cardiac catheterization
• B. A patient with new-onset atrial fibrillation
• C. A patient with stable hypertension, day 3 of admission, awaiting discharge
• D. A patient just transferred from the PACU

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Strategy Summary Card

ALWAYS RN:          Assess · Teach · Evaluate · Unstable patients
                    New symptoms · IV push meds · Care planning
                    Titrate drips · First dose of new meds · Blood

LPN CAN DO:         Routine oral/SQ/IM meds · Reinforce teaching
                    Stable dressing changes · Monitor & report
                    Routine procedures (predictable, stable)

UAP CAN DO:         Vitals (stable patients) · Bathing/hygiene
                    Ambulation (confirmed orders) · I&O recording
                    Specimen collection · Positioning

PRIORITY TRIGGERS:  Stridor · SpO2 <90% acutely · HR >120 or <50
                    Chest pain + diaphoresis · BP extremes with symptoms
                    New confusion · Active bleeding · BG <70 or >400
                    Fever in neutropenia · Suicidal plan · Limb pallor/pain

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• NursesLabs - 100 Prioritization & Delegation Questions - free, large question bank
• GoodNurse 2026 Scenarios - 25 mini-scenarios with rationales
• SimpleNursing - Patient Prioritization - visual-style explanations