A 60-year-old woman with hypertension presented with chest pain. Her initial ECG showed sinus rhythm with ST segment changes. A repeat ECG showed an atrial rhythm with P waves inverted in some leads and upright in others. This finding suggested an ectopic left atrial rhythm. A subsequent ECG reverted back to sinus rhythm similar to the initial test. The document discusses using P wave morphology, particularly in leads V1 and aVL, to differentiate between right and left atrial rhythms. A positive P wave in V1 indicates a left atrial focus while an upright or biphasic P wave in aVL suggests a right atrial origin.

1. ECG of the week Prof. P. Vijayaraghavan Unit A.KarthickRamalingam FIRST YEAR PGM 5

2. Background 60 year old Mrs. Ponnamma, known hypertensive presented with history suggestive of anginal type of chest pain, ECG was taken.

3. ECG-1

4. Findings Rate 88/min NSR P wave axis 60 QRS axis Normal ST straightening LII ,LIII, aVF T inversion L III

5. ECG-2

6. Findings Rate: 84/min Atrial rhythm P wave axis - 90 P ‘ – L II , L III, aVF ,V2 to V6 P --L I, aVR , a VL, V1 QRS axis normal T inversion L II , L III, aVF ST depression L III, aVF Findings of ectopic atrial rhythm

7. Repeat ECG taken for the patient reverted back to sinus rhythm and was similar to ECG 1

9. P wave morphology is useful in differentiating left from right atrial foci.

10. This is a function of the anatomical relationship of the atria, with the left atrium being a more posterior and leftward structure than the right atrium.

15. In our patient a positive p wave in V1 with a negative p in V6 is suggestive of a left atrial rhythm.

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