15 most common ecg in daily practice

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15 most common ECG patterns daily clinical practice interpretation

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most common ECG patterns clinical practice

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normal sinus rhythm ECG electrocardiogram

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atrial fibrillation ECG irregularly irregular rhythm

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STEMI ST elevation myocardial infarction ECG

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ventricular fibrillation ECG chaotic rhythm cardiac arrest

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left bundle branch block LBBB ECG wide QRS

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atrial flutter sawtooth waves ECG

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ventricular tachycardia wide complex tachycardia ECG

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complete heart block third degree AV block ECG pacemaker rhythm

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Wolff-Parkinson-White syndrome delta wave short PR ECG

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15 Most Common ECGs in Daily Practice

A systematic reference covering the key ECG patterns every clinician encounters, with diagnostic features and clinical pearls.

ECG Basics — Quick Reference

Parameter	Normal Value
Rate	60–100 bpm
PR interval	120–200 ms (3–5 small squares)
QRS duration	< 120 ms (< 3 small squares)
QT interval (corrected)	< 440 ms (men), < 460 ms (women)
P wave	Upright in I, II; inverted in aVR

1. Normal Sinus Rhythm

Key features:

Rate 60–100 bpm, regular
P wave before every QRS (upright in I and II, inverted in aVR)
PR interval 120–200 ms, consistent
Narrow QRS < 120 ms
Normal R-wave progression V1→V6

Clinical significance: The baseline to compare all abnormalities against. Confirm it before calling anything "sinus."

2. Atrial Fibrillation (AF)

Atrial fibrillation — irregularly irregular rhythm with absent P waves

Key features:

Irregularly irregular R-R intervals (most important clue)
No discrete P waves — replaced by fibrillatory (f) waves, best seen in V1 and II
Narrow QRS (unless aberrant conduction or WPW)
Ventricular rate typically 100–160 bpm if uncontrolled

Clinical significance: Most common sustained arrhythmia. Risk of stroke, heart failure. Requires rate/rhythm control and anticoagulation assessment (CHA₂DS₂-VASc).

"After sinus tachycardia, atrial fibrillation is the next most frequent narrow-complex tachycardia encountered in the ED." — Tintinalli's Emergency Medicine

3. Atrial Flutter

Atrial flutter with classic sawtooth flutter waves

Key features:

Sawtooth flutter waves (F-waves) at ~300 bpm, best in II, III, aVF
Regular ventricular rhythm with fixed AV conduction ratio (usually 2:1 → ventricular rate ~150 bpm)
Absent isoelectric baseline between flutter waves
Narrow QRS unless aberrant

Clinical tip: A narrow-complex tachycardia at exactly 150 bpm should always raise suspicion for 2:1 flutter. Use adenosine or carotid sinus massage to unmask the flutter waves.

4. ST-Elevation Myocardial Infarction (STEMI)

Anterior STEMI with convex ST elevation V2–V5

Key features:

New ST elevation ≥ 1 mm in ≥ 2 contiguous limb leads, OR ≥ 2 mm in ≥ 2 contiguous precordial leads
Convex ("tombstone") or straight ST morphology
Reciprocal ST depression in opposing leads
Evolving Q waves, T-wave inversion over hours

Territory localization:

Leads with STE	Territory	Culprit artery
V1–V4	Anterior	LAD
II, III, aVF	Inferior	RCA (80%) or LCx
I, aVL, V5–V6	Lateral	LCx or diagonal
V1–V4 + I, aVL	Anterolateral	Proximal LAD

Clinical significance: Time-critical emergency. Activate cath lab immediately. Door-to-balloon < 90 min.

5. Sinus Tachycardia

Key features:

Rate > 100 bpm, regular
Normal P wave morphology preceding every QRS
Rate gradually increases/decreases (not abrupt onset like SVT)
Rate typically 100–150 bpm

Common causes: Pain, fever, hypovolemia, anemia, anxiety, thyrotoxicosis, pulmonary embolism, heart failure. Treat the cause, not the rate.

6. Sinus Bradycardia

Key features:

Rate < 60 bpm, regular
Normal P wave before every QRS
Normal PR and QRS

Common causes: Athletic conditioning, vasovagal syncope, hypothyroidism, inferior MI (RCA → SA node), beta-blockers, sleep. Intervene only if symptomatic (dizziness, syncope, hemodynamic compromise).

7. Ventricular Tachycardia (VT)

Wide-complex monomorphic ventricular tachycardia

Key features:

Wide QRS > 120 ms at rate > 100 bpm
Regular rhythm, monomorphic (uniform QRS shape)
AV dissociation (P waves independent of QRS) — pathognomonic when seen
Fusion beats and capture beats (Dressler beats) — diagnostic
Concordance across precordial leads (all positive or all negative)

Brugada criteria: If wide-complex tachycardia of uncertain origin → treat as VT until proven otherwise. VT is far more common than SVT with aberrancy.

8. Ventricular Fibrillation (VF)

Ventricular fibrillation — chaotic baseline, no QRS complexes

Key features:

Chaotic, irregular, disorganized waveform
No identifiable P waves, QRS complexes, or T waves
Variable amplitude oscillations (coarse vs. fine VF)
Patient is pulseless/unresponsive

Clinical significance: Cardiac arrest. Immediate defibrillation + CPR. Shockable rhythm alongside pulseless VT.

9. Left Bundle Branch Block (LBBB)

LBBB with broad notched R waves in lateral leads and deep S in V1

Key features:

QRS > 120 ms
Broad, notched ("M-shaped") R waves in I, aVL, V5, V6
Deep QS or rS in V1 (no septal q in lateral leads)
Discordant ST-T changes (T-wave opposite to QRS)
New LBBB in the context of chest pain = treat as STEMI equivalent

Sgarbossa criteria help identify MI in the context of LBBB:

Concordant STE ≥ 1 mm (5 points)
Concordant ST depression ≥ 1 mm in V1–V3 (3 points)
Discordant STE ≥ 5 mm (2 points) — score ≥ 3 is specific for MI

10. Right Bundle Branch Block (RBBB)

Key features:

QRS > 120 ms
RSR' ("bunny ears") in V1–V2
Wide, slurred S waves in I, aVL, V5–V6
T-wave inversion in V1–V3 (secondary repolarization change — normal)
Incomplete RBBB: same pattern but QRS 100–120 ms

Clinical significance: Can be normal variant. New RBBB with anterior STE suggests proximal LAD occlusion (Sgarbossa). Also seen in pulmonary embolism (S₁Q₃T₃ + RBBB).

11. Complete (Third-Degree) AV Block

Complete heart block with AV dissociation — independent P waves and slow escape QRS

Key features:

Complete AV dissociation — P waves and QRS complexes march independently
Atrial rate faster than ventricular rate
Regular escape rhythm (junctional: narrow QRS ~40–60 bpm; ventricular: wide QRS ~20–40 bpm)
No conducted beats

Clinical significance: Requires urgent transvenous pacing or permanent pacemaker. Causes: inferior MI (often transient), anterior MI (severe, requires PPM), Lyme disease, digoxin toxicity, fibrosis.

12. Wolff-Parkinson-White (WPW) Syndrome

WPW with short PR interval, delta wave, and widened QRS

Key features:

Short PR interval < 120 ms
Delta wave — slurred initial upstroke of QRS
Widened QRS (pseudo-bundle branch block morphology)
Secondary ST-T changes ("pseudoinfarction" Q waves in inferior leads)

Clinical significance: Risk of sudden death if AF develops (rapid conduction via accessory pathway → VF). Never use AV nodal blocking agents (adenosine, verapamil, diltiazem, digoxin) in WPW + AF — this accelerates accessory pathway conduction. Use procainamide or electrical cardioversion.

13. Supraventricular Tachycardia (SVT — AVNRT/AVRT)

Key features:

Abrupt onset/termination ("paroxysmal")
Rate 150–250 bpm, perfectly regular
Narrow QRS (usually)
P waves absent, buried in QRS, or immediately after QRS (retrograde P waves — "pseudo-R'" in V1, "pseudo-S" in inferior leads)
No delta wave (differentiates from WPW)

Treatment: Vagal maneuvers → IV adenosine (6 mg rapid push) → verapamil or diltiazem if refractory. Cardiovert if hemodynamically unstable.

14. First-Degree AV Block + Mobitz I/II (Second-Degree AV Block)

First-degree AV block:

PR interval > 200 ms, every P conducts → benign, no treatment

Mobitz I (Wenckebach):

Progressive PR lengthening → dropped QRS → cycle repeats
Usually at AV node level; benign; seen in inferior MI, athletes, high vagal tone

Mobitz II:

Constant PR interval → sudden non-conducted P wave (no warning)
Below AV node (His-Purkinje); more dangerous
May progress to complete heart block → pacemaker consideration

2:1 AV block: Every other P wave blocked; cannot differentiate Mobitz I vs II from single rhythm strip — need longer recording.

15. Pulmonary Embolism Pattern (S₁Q₃T₃ + Sinus Tachycardia)

Classic ECG features of PE:

Sinus tachycardia — most common finding
S₁Q₃T₃ — S wave in I, Q wave and T-wave inversion in III
New RBBB (complete or incomplete)
Right axis deviation
T-wave inversions in V1–V4 (right heart strain)
New AF

Caveat: The S₁Q₃T₃ pattern appears in only ~20% of PE cases. A normal ECG does NOT exclude PE. Sinus tachycardia alone in the right clinical context warrants CT-PA.

Quick Summary Table

#	Pattern	Rate	Rhythm	Key Feature	Action
1	Normal Sinus Rhythm	60–100	Regular	P before every QRS	Baseline
2	Atrial Fibrillation	Variable	Irregularly irregular	No P waves	Anticoagulate; rate/rhythm control
3	Atrial Flutter	~150 (2:1)	Regular	Sawtooth F-waves	Rate control; cardioversion
4	STEMI	Variable	Usually regular	ST elevation + reciprocal changes	Activate cath lab
5	Sinus Tachycardia	> 100	Regular	Normal P wave	Treat cause
6	Sinus Bradycardia	< 60	Regular	Normal P wave	Treat if symptomatic
7	Ventricular Tachycardia	> 100	Regular	Wide QRS, AV dissociation	ACLS; defibrillate if pulseless
8	Ventricular Fibrillation	—	Chaotic	No QRS	CPR + defibrillate immediately
9	LBBB	Variable	Regular	QRS > 120ms, M-waves V5–V6	New = STEMI equivalent
10	RBBB	Variable	Regular	RSR' in V1, S in V5–V6	Rule out PE, anterior STEMI
11	Complete Heart Block	Atria fast, ventricles slow	Both regular, independent	AV dissociation	Urgent pacing
12	WPW	Variable	Variable	Short PR, delta wave	Avoid AV blockers in AF
13	SVT	150–250	Regular	Abrupt onset, narrow complex	Vagal → adenosine
14	2nd-degree AV block	Variable	Irregular	Dropped beats	Monitor; PPM for Mobitz II
15	PE Pattern	Usually tachycardia	Regular	S₁Q₃T₃, RBBB, RV strain	CT-PA to confirm

Key clinical rules to internalize:

Wide-complex tachycardia → always assume VT first
Irregularly irregular rhythm → AF until proven otherwise
HR ~150 → rule out 2:1 flutter
Short PR + delta wave → WPW — never give AV nodal blockers in tachycardia
New LBBB + chest pain → manage as STEMI

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