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    ECG Challenge: Subtle but Significant



    Question 1 Answer: The post-operative ECG shows a narrow complex tachycardia at ~110 beats/min with P-waves preceding each QRS complex that are upright in leads II, III and avF. These surface ECG characteristics are consistent with sinus tachycardia. However, considering that the patient's preoperative baseline ECG showed a significantly slower, normal heart rate in the 60 beats/min range and she is status post left atrial maze ablation, a persistent atrial arrhythmia should be suspected. Electrical reentry may occur around the linear atrial scars created by maze ablation leading to refractory left atrial arrhythmias, specifically atrial flutter (AFL) and atrial tachycardia (AT). Closer comparison of the two ECGs (Figure 2) reveals broad, biphasic P-waves in lead V1 of the pre-operative ECG (Figure 2- square) versus narrow, entirely positive P-waves in lead V1 of the post-operative ECG (Figure 2- circle).

    Figure 2. L, Pre-op ECG; R, Post-op ECGThe sinoatrial (SA) node is located at the junction between the right atrium (RA) and superior vena cava (SVC), therefore SA node activation is seen on the surface ECG as positive P-wave deflections in the inferior leads (high to low activation toward II, III, avF) and biphasic or negative deflections in lead V1 (anterior to posterior activation away from V1). The subtle finding of entirely positive P-waves in lead V1 of the postoperative ECG likely represents activation of a left atrial focus posterior to the SA node (toward V1). The right superior pulmonary vein (RSPV) is typically located just posterior to the SA node and a microreentrant circuit at the region of the RSPV may occur post left atrial maze ablation. 

    Question 2: What is the next step in managing the patient?



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