Understanding ECG: Normal vs. Abnormal Readings

Introduction

Electrocardiography (ECG or EKG) is a non-invasive test that records the electrical activity of the heart. It is used to assess heart function, detect abnormalities, and diagnose conditions like arrhythmias, heart attacks, and electrolyte imbalances.

Normal ECG Readings

A normal ECG follows a predictable pattern:

1. P Wave – Represents atrial depolarization (activation of the atria).
2. PR Interval – The time taken for electrical impulses to travel from the atria to the ventricles.
3. QRS Complex – Indicates ventricular depolarization (heart's main contraction).
4. ST Segment – Should be flat, represents the period between ventricular depolarization and repolarization.
5. T Wave – Represents ventricular repolarization (heart's recovery phase).

Normal ECG Characteristics

• Heart rate: 60-100 beats per minute.
• Rhythm: Regular with consistent intervals between beats.
• P wave before each QRS complex: This shows normal atrial conduction.
• QT interval and QRS complex within normal limits: Indicating proper electrical conduction.

Abnormal ECG Readings

An abnormal ECG can indicate various cardiac problems, categorized as follows:

1. Arrhythmias (Irregular Rhythms)

• Atrial fibrillation: Irregular, rapid beats without distinct P waves.
• Ventricular tachycardia: Rapid QRS complexes without visible P waves.
• Bradycardia/Tachycardia: Very slow (<60 bpm) or very fast (>100 bpm) heart rates.

2. Heart Block (Impaired Conduction)

• First-degree AV block: Prolonged PR interval.
• Second-degree AV block (Mobitz type 1 or 2): Intermittent failure of impulse transmission to ventricles.
• Complete (third-degree) heart block: No relationship between atrial and ventricular activity.

3. Ischemia or Myocardial Infarction (Heart Attack)

• ST Elevation: Indicates ongoing myocardial infarction.
• ST Depression: Suggests ischemia (lack of oxygen to heart tissue).
• Pathological Q Waves: Evidence of past heart attack.

4. Electrolyte Imbalances & Drug Effects

• Hyperkalemia: Tall peaked T waves.
• Hypokalemia: Flattened T waves, U waves present.
• Digoxin effect: Sagging ST segment.

Conclusion

Understanding normal and abnormal ECG readings helps in early detection and management of heart diseases. If you suspect an abnormal ECG reading, consult a cardiologist promptly for further evaluation and treatment.

Source recommendations

1. American Heart Association Guidelines for ECG Interpretation

1. https://www.heart.org/en/health-topics/heart-attack/diagnosing-a-heart-attack/electrocardiogram-ecg-or-ekg
2. https://www.ahajournals.org/doi/10.1161/circulationaha.108.191095
3. https://www.heart.org/-/media/files/affiliates/mwa/kansas-city/kc-cardiac-and-stroke-symposium/2020-event-documents/cardiac-presentations/2-ecg-hockstad.pdf?la=en
4. https://www.ahajournals.org/doi/10.1161/circulationaha.108.191098
5. https://pubmed.ncbi.nlm.nih.gov/19281932/

2. European Society of Cardiology Guidelines on Arrhythmias

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Ventricular-Arrhythmias-and-the-Prevention-of-Sudden-Cardiac-Death
2. https://academic.oup.com/eurheartj/article/43/40/3997/6675633
3. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Supraventricular-Tachycardia
4. https://pubmed.ncbi.nlm.nih.gov/36017572/
5. https://www.ahajournals.org/doi/10.1161/01.cir.0000091380.04100.84

3. American College of Cardiology Recommendations for Myocardial Infarction Diagnosis

1. https://www.acc.org/Guidelines
2. https://www.ahajournals.org/doi/10.1161/01.cir.94.9.2341
3. https://www.acc.org/
4. https://pubmed.ncbi.nlm.nih.gov/10483976/
5. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001309