Dysrhythmia Quick Reference Handbook

5-Step Rhythm Interpretation

1	Rhythm	Regular or irregular? Use calipers or paper method.
2	Rate	Count QRS in 6-sec strip ×10, or use 300 rule (300 ÷ large boxes).
3	P Waves	Present? Upright in Lead II? One P per QRS? Consistent morphology?
4	PR Interval	Measure from P start to QRS start. Normal: 0.12–0.20 sec (3–5 small boxes).
5	QRS Width	Narrow (<0.12 sec) or wide (≥0.12 sec)? Wide = ventricular origin or aberrancy.

ECG Paper Basics

Time (horizontal)

1 small box = 0.04 sec (40 ms)
1 large box = 0.20 sec (200 ms)
5 large boxes = 1.0 sec
6-second strip = 30 large boxes

Amplitude (vertical)

1 small box = 0.1 mV
1 large box = 0.5 mV
Standard calibration: 10 mm = 1 mV

Rate Calculation Methods

6-Second Method

Count QRS complexes in 6-second strip, multiply by 10.

Best for irregular rhythms.

300 Rule

Count large boxes between R waves: 300 ÷ boxes = rate.

Sequence: 300, 150, 100, 75, 60, 50

Best for regular rhythms.

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ECG Intervals & Conduction System

Normal Interval Ranges

Interval	Normal Range	Clinical Significance
PR Interval	0.12–0.20 sec	>0.20 = first-degree block; <0.12 = preexcitation
QRS Duration	<0.12 sec	≥0.12 = bundle branch block or ventricular origin
QT Interval	0.36–0.44 sec	Rate-dependent; use QTc for comparison
QTc	<450 ms (men) <460 ms (women)	>500 ms = high torsades risk

Pacemaker Hierarchy

Pacemaker Site	Intrinsic Rate	Rhythm Name if Primary
SA Node	60–100 bpm	Normal sinus rhythm
AV Junction	40–60 bpm	Junctional rhythm
Ventricles	20–40 bpm	Idioventricular rhythm

Key concept: Higher pacemakers suppress lower ones. If the SA node fails, the AV junction takes over at its slower rate.

Conduction Pathway

SA Node → Atria → AV Node → Bundle of His → Bundle Branches → Purkinje Fibers → Ventricles

AV node delay allows atrial contraction to complete before ventricular contraction begins (atrial kick).

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Sinus Rhythms

Rhythm	Rate	Key Features	Action
Normal Sinus Rhythm (NSR)	60–100	Regular, upright P before each QRS, PR 0.12–0.20	No intervention needed
Sinus Bradycardia	<60	Regular, normal P-QRS relationship, slow rate	Assess symptoms; if unstable → ACLS bradycardia
Sinus Tachycardia	>100	Regular, normal P-QRS relationship, fast rate	Treat underlying cause (pain, fever, hypovolemia, anxiety)
Sinus Arrhythmia	60–100	Irregular rhythm that varies with respiration	Normal variant; no treatment
Sinus Pause/Arrest	Variable	Sudden pause >2 sec without P wave	Assess symptoms; if frequent → consider pacing evaluation

Atrial Ectopy

Finding	Features	Action
PAC (Premature Atrial Contraction)	Early beat with abnormal P wave; narrow QRS	Usually benign; reduce triggers (caffeine, stress)
Wandering Atrial Pacemaker	At least 3 different P wave morphologies; rate <100	Usually benign; observe
Multifocal Atrial Tachycardia (MAT)	≥3 P wave morphologies; rate >100; irregular	Treat underlying cause (COPD, hypoxia, electrolytes)

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Atrial Rhythms

Rhythm	Rate	Key Features	Action
Atrial Fibrillation (AFib)	Variable (often 110–180 if uncontrolled)	Irregularly irregular; no discrete P waves (fibrillatory baseline); narrow QRS	Rate control (beta-blocker, CCB, digoxin); anticoagulation; cardioversion if unstable
Atrial Flutter	Atrial: 250–350 Ventricular: depends on block	Sawtooth flutter waves; regular or regularly irregular; common 2:1, 3:1, 4:1 conduction	Rate control; anticoagulation; cardioversion if unstable
SVT (Supraventricular Tachycardia)	150–250	Regular narrow-complex tachycardia; P waves often hidden or retrograde	Vagal maneuvers → Adenosine 6 mg, then 12 mg; if unstable → synchronized cardioversion
Atrial Tachycardia	100–250	P waves present but abnormal morphology; may have isoelectric line between P waves	Rate control; treat underlying cause

      AFib vs Flutter: Quick Comparison
      
          Atrial Fibrillation
          Atrial Flutter
        
          Regularity
          Irregularly irregular
          Regular or regularly irregular
        
          Atrial Activity
          Chaotic fibrillatory waves
          Organized sawtooth pattern
        
          Atrial Rate
          350–600
          250–350
        
          Common Ventricular Rate
          Variable
          150 (2:1), 100 (3:1), 75 (4:1)

	Atrial Fibrillation	Atrial Flutter
Regularity	Irregularly irregular	Regular or regularly irregular
Atrial Activity	Chaotic fibrillatory waves	Organized sawtooth pattern
Atrial Rate	350–600	250–350
Common Ventricular Rate	Variable	150 (2:1), 100 (3:1), 75 (4:1)

Adenosine Administration

Dose: 6 mg rapid IV push, followed by 20 mL NS flush
If no effect: 12 mg rapid IV push (may repeat once)
Site: Antecubital or more proximal preferred
Half-life: <10 seconds — must push rapidly
Warn patient: Brief chest discomfort, flushing, sense of doom is normal

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Junctional & Ventricular Rhythms

Junctional Rhythms

Rhythm	Rate	Key Features	Action
Junctional Escape	40–60	Regular; absent, inverted, or retrograde P; narrow QRS	Assess symptoms; if unstable → ACLS bradycardia
Accelerated Junctional	60–100	Same P wave characteristics; rate exceeds intrinsic junctional rate	Monitor; usually benign
Junctional Tachycardia	>100	Narrow complex; may see retrograde P after QRS	Treat underlying cause; rate control if needed

Ventricular Rhythms

Rhythm	Rate	Key Features	Action
PVC	Underlying + ectopy	Wide bizarre QRS; no preceding P; compensatory pause	Observe if isolated; treat if symptomatic or >6/min
Idioventricular Rhythm	20–40	Regular wide QRS; no P waves; ventricular escape	Assess perfusion; treat underlying cause
Accelerated Idioventricular (AIVR)	40–100	Regular wide QRS; often seen post-reperfusion	Usually benign; observe
Ventricular Tachycardia (VT)	>100 (often 150–250)	Regular wide complex; ≥3 consecutive PVCs	Pulse? If unstable → sync cardioversion; if pulseless → defibrillate
Torsades de Pointes	150–300	Polymorphic VT with twisting axis; often prolonged QT	Magnesium 2g IV; defibrillate if pulseless; correct QT
Ventricular Fibrillation (VF)	Unmeasurable	Chaotic, no organized QRS; no pulse	Immediate CPR + defibrillation
Asystole	None	Flatline; no electrical activity	CPR + epinephrine; non-shockable

      PVC Warning Patterns
      Frequent: >6/minute
Couplets: 2 in a row
Triplets: 3 in a row (= VT run)
R-on-T: PVC falls on T wave
Multifocal: Different QRS morphologies

    

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AV Blocks

Block Type	PR Interval	P:QRS Ratio	Key Features	Risk & Action
First-Degree	>0.20 sec (fixed)	1:1	Every P followed by QRS; prolonged but consistent PR	Low risk; usually observe; treat if symptomatic brady
Second-Degree Type I (Wenckebach)	Progressive lengthening	Variable (3:2, 4:3, etc.)	PR lengthens until QRS dropped; grouped beating; usually at AV node level	Moderate risk; often transient; atropine if symptomatic
Second-Degree Type II (Mobitz II)	Fixed (may be normal or prolonged)	Variable with dropped QRS	Sudden dropped QRS without PR change; usually below AV node (infra-Hisian)	High risk; may progress to complete block; prepare for pacing
2:1 AV Block	May be fixed or hard to assess	2:1	Every other P conducted; cannot distinguish Type I vs II from single strip	Treat as high risk if wide QRS or symptoms
High-Grade/Advanced	Variable	3:1 or greater	Multiple consecutive non-conducted P waves	High risk; pacing often required
Third-Degree (Complete)	N/A (no relationship)	Independent	P waves and QRS completely dissociated; atrial rate > ventricular rate	High risk; pacing required; atropine often ineffective

      Type I vs Type II: Quick Differentiation
      
          Type I (Wenckebach)
          Type II (Mobitz II)
        
          PR Pattern
          Progressive lengthening
          Fixed (constant)
        
          QRS Width
          Usually narrow
          Often wide (BBB)
        
          Block Location
          AV node
          Below AV node (His/bundle branches)
        
          Response to Atropine
          Usually improves
          Often no effect or worsens
        
          Risk of Progression
          Lower
          Higher → may progress to complete block

	Type I (Wenckebach)	Type II (Mobitz II)
PR Pattern	Progressive lengthening	Fixed (constant)
QRS Width	Usually narrow	Often wide (BBB)
Block Location	AV node	Below AV node (His/bundle branches)
Response to Atropine	Usually improves	Often no effect or worsens
Risk of Progression	Lower	Higher → may progress to complete block

Third-Degree Block: Key Points

Atria and ventricles beat independently (AV dissociation)
Ventricular rate determined by escape pacemaker (junctional or ventricular)
Narrow QRS escape = junctional (40–60 bpm)
Wide QRS escape = ventricular (20–40 bpm) — more unstable
Treatment: Transcutaneous pacing; prepare for transvenous pacing

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ACLS Algorithms

Adult Bradycardia With a Pulse

1. Identify
HR <50 with symptoms?
(Hypotension, AMS, shock, chest pain, acute HF)

↓

2. If symptomatic:
IV access, O2, monitor, 12-lead ECG

↓

          3. Atropine

          1 mg IV push q3–5 min

          Max dose: 3 mg

↓

4. If atropine ineffective:
Transcutaneous pacing
AND/OR
Dopamine 5–20 mcg/kg/min
OR
Epinephrine 2–10 mcg/min

↓

5. Consider:
Transvenous pacing
Expert consultation

Adult Tachycardia With a Pulse

1. Unstable?
(Hypotension, AMS, shock, chest pain, acute HF)

↓ YES

              Synchronized Cardioversion

              Sedate if possible

              Narrow: 50–100 J

              Wide: 100 J

↓ NO (Stable)

Assess QRS Width

Narrow (<0.12s)
Regular? Vagal → Adenosine
Irregular? Rate control

Wide (≥0.12s)
Consider VT until proven otherwise
Amiodarone or procainamide

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Cardiac Arrest & ACLS Dosing

Adult Cardiac Arrest Algorithm

Start CPR
Attach monitor/defibrillator

→

Rhythm Check

SHOCKABLE
(VF / pVT)

Shock (biphasic 120–200 J)
CPR 2 min
Epinephrine 1 mg IV q3–5 min
Shock → CPR 2 min
Amiodarone 300 mg (then 150 mg)
Repeat cycle

NON-SHOCKABLE
(Asystole / PEA)

CPR 2 min
Epinephrine 1 mg IV ASAP
Continue CPR
Epinephrine q3–5 min
Rhythm check q2 min

Treat Reversible Causes (H's and T's)
Hypovolemia, Hypoxia, Hydrogen ion (acidosis), Hypo/Hyperkalemia, Hypothermia
Tension pneumothorax, Tamponade, Toxins, Thrombosis (pulmonary/coronary)

ACLS Medication Quick Reference

Medication	Indication	Dose	Notes
Epinephrine	Cardiac arrest	1 mg IV/IO q3–5 min	Give ASAP for non-shockable
Epinephrine	Symptomatic bradycardia	2–10 mcg/min infusion	If atropine ineffective
Atropine	Symptomatic bradycardia	1 mg IV q3–5 min (max 3 mg)	May be ineffective in Type II / 3° block
Amiodarone	VF/pVT (refractory)	300 mg IV, then 150 mg	After 2nd shock in cardiac arrest
Amiodarone	Stable wide-complex tachy	150 mg IV over 10 min	May repeat; max 2.2 g/24 hr
Adenosine	Stable regular narrow-complex SVT	6 mg rapid IV push → 12 mg → 12 mg	Follow with 20 mL NS flush
Dopamine	Symptomatic bradycardia	5–20 mcg/kg/min infusion	Alternative to epinephrine infusion
Magnesium	Torsades de Pointes	1–2 g IV over 5–20 min	Load 2 g for active torsades
Lidocaine	VF/pVT (alternative)	1–1.5 mg/kg IV, then 0.5–0.75 mg/kg	If amiodarone unavailable

Cardioversion/Defibrillation Energy (Biphasic)

Defibrillation (VF/pVT)	120–200 J (or manufacturer recommendation)
Synchronized Cardioversion (narrow)	50–100 J initial
Synchronized Cardioversion (wide/AFib)	100–200 J initial

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