A 58-Year-Old Woman with Weakness and Shortness of Breath

The patient was a 58-year-old woman with a history of mitral valvuloplasty, presenting to the emergency department (ED) due to weakness and shortness of breath. Her vital signs were stable. The patient’s electrocardiogram (ECG) is presented in figure 1. What is the correct interpretation of this ECG?
1.Sinus dysrhythmia
2.Paroxysmal atrial tachycardia with variable AV node block
3.Atrial flutter with variable AV node block
4.Sinoatrial block
5.Atrial fibrillation with normal ventricular rate
The baseline rhythm of this ECG shows an irregularity at the first glance that is repeated without any specific pattern. After considering this irregular abnormal pattern, in the next step, the heartbeat in this ECG should be calculated, taking into account the irregular base rhythm, about six seconds of the ECG should be considered, and the number of complete QRS complexes should be counted in this period. The resulting number should be multiplied by ten in order to estimate the heart rate in a minute. In this patient, the heart rate was about 90 beats per minute. So far, we have an irregular abnormal rhythm in the ECG. Differential diagnosis of this condition in the ECG varies based on the wide or narrow QRS complexes. A narrow QRS complex is a sign of the natural ventricular depolarization, and several rhythms with a natural rate (60-100 beats per minute) can have irregular QRS intervals. In the case of irregular abnormal rhythms, normal rates, and narrow QRS complexes, there are various differential diagnoses, some of which are mentioned in the multiple choice answer to this question. In the following, after mentioning the electrocardiographic characteristics of each of the rhythms mentioned in the question and their simultaneous assessment in this ECG, we will reach the correct answer.