Case
Hi, I’m calling about a 9-month old infant, that you follow, with supraventricular tachycardia. She presented today after the parents noted that her heart rate was elevated to our urgent care. Heart rate was steady at about 220 bpm and mom said they first noted it about 2 h ago. We were able to apply ice to the face and forehead a couple of times that seemed to slow it down but really didn’t break it. Then as we were getting an IV, the tachycardia broke. Right now, she looks great, comfortable, and has a heart rate of 120 bpm. She is on propranolol and mom says she’s been getting her doses. I’d like to send her home but wondering if there is anything you would like me to do?
What am I thinking?
First thing is I am relieved to hear that the tachycardia has broken but now it is a matter of making sure that we prevent it from initiating again. Under these circumstances, I likely have an idea of who this family is and what type of tachycardia I am dealing with. Given the age and heart rate, I am likely dealing with an accessory pathway-mediated reentrant supraventricular tachycardia. It sounds like I have been treating with β-blockers but the one thing about this age is the growth that these infants can experience in a short period of time. I should be thinking about the dose and if it is still appropriate for the infant’s size. Given a heart rate of 120 bpm at rest, we may have some room to increase. If not, maybe we try another medication in addition or switch altogether. Ultimately, we have options. Once I have adjusted the medication, it is probably time to bring the family back in and repeat discussions around monitoring and vagal maneuvers.
| Differential diagnosis |
|---|
| Likely |
Supraventricular tachycardia
|
| Possible |
Supraventricular tachycardia
|
| Rare |
| Multifocal atrial tachycardia Ventricular tachycardia Second form of supraventricular tachycardia Proarrhythmic effects from medication overdosing |
History and physical
Infants who present with recurrence of their tachycardia should start with an evaluation of their current treatment regimen. A single breakthrough episode in a patient with SVT is not a cause for alarm and does not immediately merit a change of plan. For those who are on medication, a clear understanding of the type of medication and the “target” dose when prescribed is essential to understand the next steps. Target dose refers to the dose per body weight or body surface area achieved. As infants undergo rapid growth, this dose is frequently outgrown and thereby interferes with the appropriate steady-state of the medication. A review of any missed dosing or changes in dosing should also be assessed. As the medication provided to infants is a solution or suspension, the concentration of the medication and any pharmacy changes may lead to a change in dosing given that parents often are more cognizant of a medication amount (i.e., milliliters) versus a dose (milligrams). Finally, a review of medication tolerance should be sought with the parents. It is not uncommon for parents to forego medications if they feel that their infant is not tolerating the medication or that there are challenges with administration, including cost.
As with any infant with tachycardia, physical examination should focus on signs of hemodynamic stability to determine the need for immediate action. Temperature, respiratory rate, oxygen saturation, pulses, hepatomegaly, and capillary refill are some of the signs to be evaluated for the possibility of cardiomyopathy secondary to arrhythmia.
Recurrent supraventricular tachycardia (SVT) in an infant can be a source of great anxiety and inconvenience to parents. In general, infants are first diagnosed with SVT after some form of clinical symptomatology that usually involves anxious and hurried visits to medical care. This is usually followed by the initiation of medication and monitoring with equipment not available for home use. Finally, after a return to some level of normalcy for the infant, the parent is quickly educated on the importance of providing these medications on a strict schedule, asked to monitor for any recurrences with limited resources, and to follow up with a heart doctor. Recurrence can be perceived by parents as parenting failure, worsening of condition, or a worsening prognosis—all of which are not true.
Diagnostic testing
The standard electrocardiogram is the best test to assess rhythm and is particularly helpful in the infant with tachycardia recurrence. Presumably, the infant’s previous tachycardia has been documented on electrocardiogram and can be utilized for comparison (see Fig. 6.1 ). Subtle changes in an electrocardiogram may clue the trained electrophysiologist if there are changes in the arrhythmia or if the tachycardia represents a second form. Any attempts to modify or break the tachycardia should be captured on a running rhythm strip, preferably with multiple leads as with a standard electrocardiogram. Documentation of the response of the SVT to vagal maneuvers or drug treatment like adenosine can provide significant clues about the type of arrhythmia and its likely response to therapy.
