Case
Hi, I’m calling you about a 22-year old female who I follow here in GI clinic due to her diagnosis of single ventricle palliation with a Fontan and her subsequent development of protein losing enteropathy. She comes in for routine follow-up and from her PLE standpoint, she’s actually doing great. But today she’s complaining that over the last two weeks she’s been feeling very tired and has a lack of energy. I put her on a pulse oximeter in clinic and her oxygen saturation is 95%, which is what it has been in the past. But the machine is reading her heart rate at 110 bpm. I looked back on my notes and her heart rate usually runs 70–80 bpm so this seems a little fast to me. She doesn’t appear dehydrated and she isn’t febrile. I’m sending her for some baseline GI labs. She’s been waiting for about an hour and a half due to a back up in the lab and I’ve kept the pulse oximeter on her finger to monitor her heart rate. It has stayed persistently at 110 bpm without any variation. I’m a little worried something might be going on.
What am I thinking?
Patients with congenital heart disease who have undergone surgical intervention are at risk for the development of arrhythmias. This is related to the development of areas of scar in areas of suture or patches that can serve as substrates for arrhythmia circuits. Arrhythmias may be atrial or ventricular in origin depending on the region of surgical work performed. For patients who have manipulation of atrial tissue such as an atrial switch procedure (Mustard or Senning) for transposition of the great arteries or the Fontan operation for single ventricle physiology, can be a set up for atrial reentrant rhythms. Patients who have had work performed in the ventricle such as tetralogy of Fallot would be at risk of ventricular tachycardia. These patients should be under the care of a pediatric or adult congenital cardiologist and/or electrophysiologist.
In the scenario presented, the patient presents with a heart rate of 110 bpm. While this rate is not exceedingly high, it is suggestive of an arrhythmia, particularly in the congenital heart patient who has undergone palliation. Persistent arrhythmias at these moderately tachycardic rates in patients with palliated heart disease may result in cardiac dysfunction. Patients can present with symptoms of congestive heart failure including fatigue, pulmonary edema, and respiratory insufficiency.
For those patients with atrial arrhythmias, the ventricular rate is dependent on the conduction through the AV node and can be protective from further symptomatology or sudden decompensation. Therefore, an atrial rate between 220 and 300 bpm that is blocked 2:1 may result in a pulse rate of 110–150 bpm. Careful analysis of the electrocardiogram can demonstrate additional P waves suggestive of an intraatrial reentrant tachycardia (IART) (see Fig. 29.1 ). Additional clues that an IART may be occurring is the lack of heart rate variability when in the arrhythmia (see Fig. 29.2 ). The consistency in the rhythm is based on the defined circuit, usually circling a valve or area of the scar. If there are changes in heart rate, they may be resulting from varying AV conduction and are usually seen as changes from 2:1 to 3:1 conduction. In some situations, AV conduction can be enhanced leading to a sudden change in rate to 1:1 conduction and hemodynamic collapse, particularly in the patient with less than normal cardiac function.
