ECG Interpretation

Machine-Reported Parameters

Systematic Interpretation

• Heart rate: 69 bpm - normal
• Regular R-R intervals
• Normal sinus rhythm: upright P waves in I, II, aVF; inverted in aVR; every P followed by a QRS

• QRS axis ~+71° - normal axis (between -30° and +90°)
• P axis ~70°, T axis ~54° - both normal

• Duration 102 ms - normal (no atrial enlargement)
• Morphology normal in all leads

• 158 ms - normal; no first-degree AV block, no pre-excitation (delta waves absent)

• Duration 96 ms - narrow; no bundle branch block
• Voltage: RV5 = 2.279 mV (22.79 mm) + SV1 = 1.303 mV (13.03 mm) = 3.582 mV (35.82 mm)
• This meets the Sokolow-Lyon criterion for Left Ventricular Hypertrophy (LVH) (threshold: ≥3.5 mV / 35 mm)
• The precordial leads show tall R waves in V4-V6 consistent with LVH

• T axis 54° - concordant with QRS axis (normal)
• On visual review: lateral leads (V5-V6, I, aVL) should be assessed for LVH-related repolarization changes (strain pattern - ST depression with asymmetric T wave inversion). The image suggests possible strain pattern in the lateral leads.

• QTc 405 ms - within normal limits for a female (<440 ms)

Summary / Impression

Normal Sinus Rhythm at 69 bpm with Left Ventricular Hypertrophy (LVH) by voltage criteria (Sokolow-Lyon)

• All intervals (PR, QRS, QTc) are within normal limits
• No evidence of bundle branch block, AV block, or acute ischemic changes
• No arrhythmia

Clinical Considerations

1. Hypertension (most common cause) - check BP
2. Aortic stenosis or other valvular disease
3. Hypertrophic cardiomyopathy
4. Echocardiogram is recommended to confirm LVH anatomically and assess wall thickness, chamber size, and systolic/diastolic function

Note: This is an ECG interpretation aid only. Clinical correlation and physician review are essential for diagnosis and management.

Re-assessment: Irregular Rhythm in Lead II

Differential Diagnosis Based on Irregularity Pattern

1. Sinus Arrhythmia (most benign)

• R-R intervals vary gradually, typically with breathing (longer on expiration, shorter on inspiration)
• P wave morphology is the same before every QRS
• Common in young/athletic individuals; also seen in the 40-50 age group
• PR interval remains constant throughout

2. Premature Atrial Contractions (PACs)

• One or more beats come early (short R-R)
• Followed by a non-compensatory pause
• P wave before the early beat looks different (different morphology/axis) or may be buried in the preceding T wave
• QRS is narrow (unless aberrantly conducted)

3. Premature Ventricular Contractions (PVCs)

• One or more beats come early with a wide, bizarre QRS (different morphology)
• Followed by a full compensatory pause
• No preceding P wave (or dissociated P wave)
• T wave is opposite in direction to the QRS

4. Atrial Fibrillation (AF)

• Irregularly irregular - no two R-R intervals are the same, with no pattern
• No discernible P waves - replaced by chaotic fibrillatory baseline
• QRS complexes are narrow (unless aberrant)
• This is important to exclude given LVH found on this ECG (LVH is a risk factor for AF)

5. Second-Degree AV Block (Mobitz I / Wenckebach)

• PR interval progressively lengthens until a QRS is dropped
• Then the cycle repeats
• Creates a characteristic "grouped beating" pattern

What to Look For in Lead II

Clinical Relevance in This Patient

• LVH increases risk of both PACs/PVCs and atrial fibrillation
• If AF is present, it warrants anticoagulation assessment (CHA₂DS₂-VASc score)
• If frequent PVCs, 24-hour Holter monitoring is recommended

• Are there occasional early beats (PAC/PVC)?
• Or is the rhythm completely chaotic throughout (AF)?
• Or does the rhythm vary in a cyclic pattern (sinus arrhythmia)?

Irregular Rhythm + P Waves Present

Top Differentials

1. Sinus Arrhythmia (Most Likely)

• P waves present before every QRS, all same morphology
• PR interval constant throughout
• R-R intervals vary in a cyclical pattern with respiration
• Completely benign - no treatment needed
• How to confirm: Ask patient to hold breath - irregularity should disappear or reduce

2. Premature Atrial Contractions (PACs) (Very Common)

• Occasional early beat with a P wave that looks slightly different (peaked, biphasic, or different axis)
• The early P may be hidden in or distorting the preceding T wave
• Followed by a non-compensatory pause (the pause after the early beat is less than 2× the normal R-R)
• QRS after the PAC is narrow (same as normal beats)

3. Wandering Atrial Pacemaker (WAP)

• P wave is present before every QRS
• But P wave changes shape beat to beat (at least 3 different P morphologies)
• PR interval varies slightly
• Rate typically normal (<100 bpm) - fits this patient's 69 bpm
• Reflects shifting pacemaker focus between SA node, atrial tissue, and AV junction
• Generally benign but can be a precursor to multifocal atrial tachycardia

4. Second-Degree AV Block - Mobitz I (Wenckebach)

• P waves present and all look the same
• PR interval progressively lengthens with each beat
• Eventually one P wave is not followed by a QRS (dropped beat)
• After the pause, the cycle resets
• Creates a "grouped beating" pattern

5. Multifocal Atrial Rhythm

• P waves present but with ≥3 different morphologies
• Irregular R-R intervals
• Rate <100 bpm (unlike multifocal atrial tachycardia)
• Associated with pulmonary disease, electrolyte imbalance

Key Distinguishing Questions

Most Probable Interpretation for This ECG

• Female, ~50 years, HR 69 bpm
• LVH by voltage
• Irregular rhythm with P waves present
• PR interval reported as 158 ms (normal)

1. Sinus arrhythmia - if P waves all look the same and irregularity is breath-related
2. PACs - if there are occasional early narrow beats with slightly different P morphology
3. Wandering Atrial Pacemaker - if P wave morphology changes from beat to beat

• Measure R-R intervals manually across the Lead II strip
• Compare P wave morphology beat by beat
• Check if PR interval is constant or varies
• 24-hour Holter monitor to characterize the arrhythmia burden
• Echocardiogram (already indicated for LVH)
• Check electrolytes (K⁺, Mg²⁺) and thyroid function