Which dysrhythmia is suspected in a toddler with a heart rate of 220 bpm and prolonged capillary refill after 2 days of vomiting?

In a toddler exhibiting a heart rate of 220 bpm and prolonged capillary refill after two days of vomiting, the most likely diagnosis is supraventricular tachycardia (SVT). SVT is characterized by a rapid heart rhythm originating above the ventricles, typically caused by reentry circuits within the atria or atrioventricular (AV) node. The high heart rate indicated suggests a significant tachyarrhythmia, which aligns with the features of SVT.

The prolonged capillary refill time can be indicative of poor perfusion, often resulting from the increased heart rate that may compromise cardiac output. In young children, conditions that can lead to dehydration, such as excessive vomiting, can exacerbate these symptoms and trigger episodes of SVT. The rapid heart rate and associated signs of inadequate perfusion in this setting emphasize the need to consider SVT.

Other conditions, such as atrial fibrillation or rapid pulmonary flutter, are less common in toddlers, while bradycardia is characterized by a slow heart rate rather than a high one. Hence, the presentation strongly supports the diagnosis of SVT in this scenario.