Case
Sorry to bother you, I’m calling from the emergency room at Blank Regional Hospital, we’re about 90 miles from your institution. We had a 7-year old female who has a history of supraventricular tachycardia (SVT) that presented with breakthrough tachycardia today at 220 bpm. I tried having her blow through an occluded straw and she was unable to break the tachycardia- this usually works for her. I was able to obtain an ECG and I am sending that to you now. I was going to give her adenosine 6 mg IV but the tachycardia broke as we were getting an IV. The reason I am calling you is that this is her fourth visit to the ER for this SVT. She was seen by a local adult cardiologist who had put her on a calcium channel blocker after her second visit, but it really hasn’t worked. According to the mother, she is having breakthrough episodes nearly every day at school and they self-resolve after sitting in the nurse’s office for about 30 minutes. They were told that anything longer she should seek medical attention. Her dose on the calcium channel blocker is pretty good for her weight and she has had some significant constipation issues with it. I’m wondering if I should try a different medication or have her come see you?
What am I thinking?
Whenever I hear a story like this, I am often left wondering why I haven’t seen this child sooner ? The rate of 220 and the ability to break with vagal maneuvers are very consistent with a reentrant tachycardia that is AV nodal dependent. Atrioventricular reentrant tachycardia is the most likely secondary to an accessory pathway given her age. Having breakthrough tachycardia daily is unacceptable, especially at this age. My inclination is to have a visit with the family and seriously discuss the option of catheter ablation, or a trial of a different medication.
| Differential diagnosis |
|---|
| Likely |
| Atrioventricular reentrant tachycardia (AVRT), accessory pathway mediated Atrioventricular nodal reentrant tachycardia (AVNRT) |
| Possible |
| Ventricular tachycardia, outflow tract |
| Rare |
| Ectopic atrial tachycardia |
History and physical
In the child or adolescent who is having recurrent arrhythmias, an arrhythmia history can be very helpful in guiding treatment and understanding potential mechanisms. For the child with SVT, the sensation can be difficult to explain and is often expressed in their imaginative way. Children may state that their heart is “running” or “beeping” very fast. Some may simply complain that their “heart hurts” given limited ability to express tachycardia and not reflecting true angina. Children are usually quite perceptive of the sudden onset of tachycardia though the sudden offset is less recognized. They are often quite clear when they are in tachycardia and when they are not. Common complaints associated with tachycardia is the feeling of lightheadedness or dizziness, shortness of breath, and all accompanied by the feeling that the heart is “beating out” of the chest. Some express the feeling of nausea and on occasion chest discomfort, though not often found to have true cardiac chest pain. Rarely do children present with syncope and this may warrant further workup for other arrhythmias or inherited arrhythmia syndromes. Family members will often say that the child does not look right during the episode, usually appearing slightly pale and “out of it.” Smaller children often choose to stop involvement in activities and wish to rest. Older children are quite clear that something feels off and left to their own devices, will look to rest.
Attention is often turned to triggers the start of the tachycardia. Most commonly physical activity is a trigger for reentrant tachycardias. This may be a result of alterations in the AV nodal conduction and refractory zones or an increase in ectopic beats. Often, older children will complain that when they are participating in physical education or playing sports, they note the SVT. In such instances, we often advise that they should discontinue actively playing and attempt to break the tachycardia on the sidelines. Once the tachycardia has ceased, return to activity is allowed after approximately 10 min of rest.
For some, a trigger may be dietary and related to caffeine intake such as in sodas, coffees, or energy drinks. Caffeine can increase the frequency of ectopic beats such as premature atrial and premature ventricular beats. This increase in ectopy can lead to frequent tachycardias. Understanding potential triggers can help in planning for electrophysiology study and needs for induction of tachycardia (e.g., use of beta-agonist such as isoproterenol). Physical examination is primarily focused on the determination of an associated structural heart problem; however, this is uncommon.
For patients who are considered candidates for electrophysiology study and ablation, there are aspects of the history and physical that should be ascertained. It is wise to ask about the family history regarding any bleeding disorders or bleeding tendencies (i.e., von Willebrand, heparin-induced thrombocytopenia), likewise clotting disorders or clotting tendencies (i.e., Factor V Leiden). Most studies in the young are performed under general anesthesia, asking for family or personal history of anesthesia reactions including malignant hyperthermia. Asking family about other members who have undergone a cardiac ablation or catheterization can help to gauge their understanding of the procedure. Determining other past medical histories such as diabetes or asthma can also help with planning. Patients will need to fast before the procedure and special care has to be taken in diabetics to manage their blood sugar appropriately. Adenosine, which is often used in the procedure, can induce significant bronchospasm in some patients with asthma and the anesthesiologist should be alerted before administration. As intubation is required for general anesthesia, knowing about loose teeth or any neck deformities is best known ahead of time. From a physical examination standpoint, the focus should be on clearly understanding vascular access points and if there are any obstructions such as the previous history of femoral catheterization or central line placement. Additionally, those patients who suffer from physical disabilities may have significant issues with lying on a table supine for several hours or may have contractures that prevent proper positioning.
Diagnostic testing
For patients preparing for an electrophysiology study and ablation, several tests can provide critical information. The first is the electrocardiogram at baseline to determine if ventricular preexcitation is present (see Figs. 13.1 and 13.2 ). An electrocardiogram of the tachycardia will also be helpful as certain appearances can indicate mechanism and pathway location. If the onset and offset were able to have been caught on an electrocardiogram or monitor strip, this can also be very helpful.
An echocardiogram is necessary to determine the cardiac anatomy and assessment of cardiac function. Special attention should also be focused on vascular abnormalities such as an interrupted inferior vena cava or left superior vena cava to the coronary sinus. The finding of an atrial communication may also influence decisions regarding the transseptal approach and timing of heparinization during the procedure.
If there are any questions regarding vascular patency due to prior history of cannulation, a vascular study should be performed before the procedure to verify. For female patients who have the potential for pregnancy, a pregnancy test must be ordered given the radiation exposure with fluoroscopy.
Action plan
The decision to proceed with an electrophysiology study and catheter ablation can be a difficult one for families. The Pediatric and Congenital Electrophysiology Society along with the Heart Rhythm Society has published comprehensive and thorough guidelines regarding indications for ablation in children. Generally, patients who are at least 15 kg and ages 7–8 years who are experiencing recurrent tachycardia that is either refractory to medical therapies, results in ventricular dysfunction, or requires frequent emergency room visits are considered good candidates for ablation with safe and effective outcomes.
When discussing the treatment of the standard narrow complex SVT child, there are several options presented to the parents. The first is to continue to monitor without intervention. This is usually reserved for the child who has a rare occurrence of SVT (say once per year) that is short in duration or can be easily broken without the need for medical services. The second option is to initiate and modify medications for those patients that have recurrent SVT. First line agents can include digoxin, β-blockers, or calcium channel blockers and various combinations of the three. Sodium channel blockers and class III agents are generally felt to be the second line. The risks of medications include potential side effects as well as the need for compliance with at least daily and often multiple doses per day. The benefit is that the patient can avoid a procedure, and in some cases, can avoid any further SVT with a medication taken once daily.
Finally, the option of catheter ablation for children who have multiple recurrences of SVT who may be refractory to medications or wish to have a more permanent solution to their tachycardia. Patients are brought to the cardiac catheterization lab where fluoroscopy equipment can be used to guide catheters to the heart. With three-dimensional mapping systems, the modern era of ablation has entered a low to zero-fluoroscopy model, minimizing the amount of radiation to the patient. As was mentioned previously, most electrophysiology studies and ablations are performed under general anesthesia or deep sedation in children. The patient is prepped and draped in a sterile fashion.
Access is obtained in various vascular structures, usually the femoral veins bilaterally. Right internal jugular and femoral arterial access may be obtained. Using a modified Seldinger technique, sheaths of various sizes are placed in the access locations to be able to place and exchange catheters that are long, coated wires that contain electrodes at the distal tip capable of recording the local electrical activity at the adjacent cardiac tissue. Electrical potentials can also be sent through the catheter to activate the adjacent cardiac tissue or “pace” the heart leading to a cardiac contraction. These catheters are placed into various positions of the heart to obtain signals from structures such as the sinus node (high right atrial catheter), atrioventricular node (His catheter), ventricle (right ventricle catheter), and the mitral valve annulus (coronary sinus catheter) (see Fig. 9.1 ). With catheters in place, an electrophysiology study is performed using various diagnostic techniques involving pacing to understand the baseline electrical system and induction of arrhythmia. Based on the pattern of activation and other diagnostic maneuvers, the mechanism of arrhythmia can be deduced (see Figs. 9.2 and 9.3 ).
