Introduction
Tachycardia refers to a condition where the heart rate rises above 100 beats per minute at rest. It is not a disease itself, but a clinical sign that may indicate underlying physiological stress or cardiac electrical disturbances.
Proper interpretation of tachycardia on ECG is essential because different rhythms require completely different emergency approaches.
The evaluation mainly depends on:
- QRS duration (narrow or wide)
- Rhythm pattern (regular or irregular)
Classification of Tachycardia
| QRS Type | Regular Rhythm | Irregular Rhythm |
|---|---|---|
| Narrow QRS | Sinus tachycardia, AVNRT, AVRT, atrial tachycardia, atrial flutter (fixed block) | Atrial fibrillation, MAT, atrial flutter (variable block) |
| Wide QRS | Monomorphic VT, SVT with aberrancy | Polymorphic VT, Torsades de Pointes, AF with aberrancy |
1. Sinus Tachycardia
ECG Characteristics
- Normal P waves preceding every QRS complex
- Heart rate typically 100–150 bpm
- Gradual onset and termination
- Rate varies with physiological demand
Common Triggers
- Fever and infection
- Anxiety or emotional stress
- Dehydration
- Blood loss or anemia
- Hypoxia
- Hyperthyroidism
- Pulmonary embolism
Management
Treatment is directed at the underlying cause:
- Fluids for dehydration
- Antipyretics for fever
- Oxygen therapy for hypoxia
- Pain or anxiety control
Heart rate control drugs are rarely required unless the condition is inappropriate sinus tachycardia.
2. Supraventricular Tachycardia (SVT)
Includes AVNRT, AVRT, and atrial tachycardia.
A. AVNRT (AV Nodal Re entry Tachycardia)
ECG Findings
- Regular narrow complex tachycardia
- Rate between 150–250 bpm
- P waves usually hidden
- Pseudo R’ may appear in V1
Treatment
Stable patient:
- Vagal maneuvers first
- IV Adenosine 6 mg → then 12 mg if needed
Unstable patient:
- Immediate synchronized cardioversion
Long term:
- Catheter ablation is curative in most cases
B. AVRT (Wolff Parkinson White related)
ECG Findings
- Narrow complex tachycardia
- Retrograde P waves after QRS
- RP interval longer than PR interval
Treatment
- Vagal maneuvers
- Adenosine (only if stable and no pre-excited AF)
Avoid AV nodal blockers in atrial fibrillation with WPW.
C. Atrial Tachycardia
ECG Findings
- Abnormal P waves before QRS
- Regular rhythm
- Rate 100–200 bpm
Treatment
- Beta blockers or calcium channel blockers
- Adenosine may terminate some cases
- Ablation for recurrent episodes
3. Atrial Flutter
ECG Features
- Sawtooth pattern (flutter waves)
- Best seen in inferior leads (II, III, aVF)
- Atrial rate 250–350 bpm
- Often 2:1 conduction → ventricular rate ~150 bpm
Management
Stable:
- Rate control with diltiazem or verapamil
- Ibutilide for conversion
Unstable:
- Electrical cardioversion (50–100 J)
Definitive:
- Radiofrequency ablation
4. Atrial Fibrillation
ECG Features
- No identifiable P waves
- Irregularly irregular rhythm
- Variable ventricular rate (110–160 bpm)
Treatment Approach
Rate Control
- Metoprolol
- Diltiazem
- Digoxin (selected cases)
Target: <110 bpm
Rhythm Control
Used in:
- Symptomatic patients
- New onset (<48 hours)
- Young individuals
Options:
- Flecainide or propafenone (no structural heart disease)
- Amiodarone
- Electrical cardioversion (200 J)
Stroke Prevention
Based on CHA₂DS₂-VASc score:
- DOACs (apixaban, rivaroxaban)
- Warfarin when indicated
Unstable AF
- Immediate synchronized cardioversion
5. Multifocal Atrial Tachycardia (MAT)
ECG Findings
- At least three different P wave morphologies
- Irregular rhythm
- Rate >100 bpm
Association
- Common in COPD and chronic lung disease
Treatment
- Treat underlying lung condition
- Oxygen support
- Verapamil or beta blockers may help
Cardioversion is ineffective
6. Junctional Tachycardia
ECG Features
- Narrow QRS
- Rate 100–180 bpm
- Retrograde or absent P waves
- Possible AV dissociation
Causes
- Digoxin toxicity
- Post-cardiac surgery
- Myocarditis
Management
- Stop offending drug
- Beta blockers
- Amiodarone if needed
7. Ventricular Tachycardia (VT)
8. Monomorphic VT
ECG Features
- Wide QRS complexes
- Uniform morphology
- AV dissociation may be present
Treatment
Stable:
- Amiodarone or procainamide
Unstable:
- Synchronized cardioversion (100–200 J)
Avoid calcium channel blockers
9 .Torsades de Pointes
ECG Features
- Polymorphic VT with twisting pattern
- Prolonged QT interval
Causes
- QT-prolonging drugs
- Hypokalemia
- Hypomagnesemia
- Congenital long QT
Treatment
- IV magnesium sulfate 2 g
- Correct electrolytes
- Stop causative drugs
- Overdrive pacing if recurrent
10. Ischemic Polymorphic VT
- Treat with amiodarone
- Urgent coronary reperfusion
11. Ventricular Fibrillation (VF)
ECG Appearance
- Chaotic, irregular electrical activity
- No organized QRS complexes
- No cardiac output
Emergency Management
- Immediate defibrillation
- CPR
- Epinephrine during resuscitation
- Amiodarone after repeated shocks
Stability Based Approach
Unstable Patient
- Immediate synchronized cardioversion or defibrillation
- Do not delay for ECG classification
Stable Patient
- Detailed ECG analysis
- Drug-based management depending on rhythm type
Quick Reference Table
| Rhythm | Key Feature | QRS | Treatment |
|---|---|---|---|
| Sinus tachycardia | Normal P waves | Narrow | Treat cause |
| AVNRT | Hidden P waves | Narrow | Adenosine |
| AVRT | Retrograde P | Narrow | Adenosine (caution WPW AF) |
| Atrial tachycardia | Abnormal P | Narrow | Beta blockers |
| Atrial flutter | Sawtooth waves | Narrow | Diltiazem / cardioversion |
| Atrial fibrillation | Irregular rhythm | Narrow | Rate control + anticoagulation |
| MAT | Multiple P waves | Narrow | Treat lung disease |
| Junctional tachycardia | Retrograde P | Narrow | Remove cause |
| VT | Wide QRS | Wide | Amiodarone / cardioversion |
| Torsades | Twisting pattern | Wide | Magnesium |
| VF | Chaotic rhythm | Wide | Defibrillation |
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