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Syncope, or fainting, can be a frightening event, especially in the pediatric population. The causes are often benign and can include dehydration and postural hypotension. However, there are multiple etiologies of arrhythmogenic syncope, many of which can be life threatening. Knowledge of the potential causes, work-up, and treatment of arrhythmogenic syncope may be the difference between life and death in affected patients.
Can you identify and manage the following two adolescent cases of arrhythmogenic syncope?
Image of the transmission of a cardiac action potential through the normal cardiac conduction system courtesy of Wikipedia/Kalumet. The red lines represent the depolarization wave, not blood flow.
An 18-year-old previously healthy female presents to the emergency department (ED) via ambulance following a syncopal event. She reported that she was walking down the stairs at home when she began to feel her heart racing. When she neared the bottom of the stairs, she felt dizzy and was found unconscious by her parents. After approximately 2 minutes, she woke up and was alert and oriented. There was no evidence of injuries, including head trauma. Emergency medical services (EMS) arrived several minutes later.
Image of the interior view down the spiral staircase of the Weizmann house tower, Rehovot, Israel, courtesy of Wikimedia Commons/MartinVMtl.
The patient's vital signs during transport to the local ED were as follows:
In the ambulance, she was alert and answered questions appropriately. She reported continuing to feel her heart race as well as having mild dizziness while lying down.
The paramedics placed her on a cardiac monitor and obtained the electrocardiographic (ECG) rhythm strip shown.
What do you note about the rhythm?
Adapted ECG courtesy of CardioNetworks/WG de Voogt, MD, PhD, SLAZ, The Netherlands, via Wikimedia Commons.
Answer: The rhythm strip demonstrates a wide-complex tachycardia.
The rhythm is not regular (as denoted by the different RR intervals), and it could be described as irregularly irregular. Additionally, note the absence of obvious P waves.
On arrival to the ED, the patient's level of alertness has not changed, and her vital signs remain stable. Her cardiac examination reveals an irregular rhythm, no evidence of murmur, and 2+ pulses in her distal extremities.
What are the next steps in the evaluation and work-up of this patient?
Adapted ECG courtesy of CardioNetworks/WG de Voogt, MD, PhD, SLAZ, The Netherlands, via Wikimedia Commons.
Answer: Obtain large-bore intravenous (IV) access, baseline electrolyte levels, and a 12-lead ECG. In addition, place external defibrillator pads on the patient's bare chest.
The patient's 12-lead ECG is shown. Which of the following arrhythmias does the ECG reveal?
Adapted ECG courtesy of CardioNetworks/WG de Voogt, MD, PhD, SLAZ, The Netherlands, via Wikimedia Commons.
Answer: B. Atrial fibrillation (AF) with rapid ventricular response
In the ED, the patient continues to be alert with stable vital signs. Therefore, you decide to treat with IV diltiazem for AF. After receiving the IV treatment, she loses consciousness, and her cardiac rhythm changes on the monitor.
What is the rhythm shown, and what is the next step in this patient's management?
Image courtesy of Jason E Roediger, CCT, CRAT, via Wikimedia Commons/Jer5150.
Answer: The rhythm is ventricular fibrillation. Administer chest compressions and rapid defibrillation.
Chest compressions are initiated, and external defibrillation with 50J is performed. Chest compressions are continued after the electric shock is delivered. After 2 minutes, a rhythm check reveals conversion to normal sinus rhythm.
The patient's vital signs normalize and, again, she is awake and alert. After her stabilization, you obtain a repeat ECG while she is in sinus rhythm (shown).
What are the abnormal findings on the ECG, and what is the diagnosis?
Image courtesy of Bradley C Clark, MD.
Answer: The ECG shows the classic findings of Wolff-Parkinson-White (WPW) syndrome.
The hallmark findings of WPW syndrome include a short PR interval and a delta wave.[1] The delta wave occurs due to the presence of an accessory electrical connection between the atrium and ventricle (which can occur on both the left and right side of the heart) that bypasses the normal conduction system.
WPW syndrome was first described by Wolff, Parkinson, and White in 1930.[2] Patients with this syndrome are often asymptomatic unless they develop reentrant supraventricular tachycardia (SVT) or AF with rapid ventricular response.
Reentrant SVT in WPW syndrome occurs due to the presence of two different limbs of a circuit with different electrical properties. In order for the circuit to cause tachycardia, one limb of the pathway must be refractory to electrical input during antegrade depolarization, and the other limb must have an area of slow retrograde conduction that allows the initial limb to recover and accept the return stimulus.[3]
Image courtesy of Bradley C Clark, MD.
The work-up in patients with WPW syndrome should include exercise stress testing to determine the heart rate at which the preexcitation disappears.[1]
Image of an ergospirometry laboratory for the measurement of metabolic changes during a graded exercise test on a treadmill courtesy of Wikipedia/Cosmed.
WPW syndrome is associated with a low risk of sudden cardiac death. Accessory pathways that can conduct at high heart rates (>250 bpm) have an increased vulnerability of rapid ventricular conduction during AF, with the potential for degeneration to VF.[4] Thus, the presence of an accessory pathway in WPW syndrome creates an additional risk of developing AF and, potentially, VF and sudden death.[1]
For this reason, which of the following medications are contraindicated in WPW syndrome? (More than one choice may be possible.)
Image courtesy of Wikipedia/Tom Lück.
Answers: B. Calcium channel blockers and C: digoxin
Both calcium channel blockers (eg, diltiazem, verapamil) and digoxin decrease the refractory period of the accessory pathway, thereby increasing the risk of conduction down that pathway.[1,5-9] Specifically, in the setting of AF, this higher risk of conduction along the accessory pathway elevates the likelihood of the development of a rapid ventricular response and VF.
Image courtesy of Olivia Wong, DO.
The treatment of WPW syndrome depends on the presence of symptoms.[1] In the absence of the development of tachycardia (SVT or AF), no treatment is typically required.
In cases of documented arrhythmia, first-line therapy includes a beta-blocking agent (eg, metoprolol, atenolol) to prevent further episodes of arrhythmia. In adolescents and adults with WPW syndrome and documented tachycardia, the definitive treatment is ablation of the accessory pathway.[10]
Image courtesy of Wikimedia Commons/Calleamanecer.
Arrhythmia ablation is performed using catheter access to the heart. The procedure can be performed utilizing either cryoablation (freezing) or radiofrequency (heating).[1,11]
Catheter access is gained through the femoral veins and inserted into the heart. Using specialized three-dimensional (3D) mapping technology and electrical testing, the electrophysiologist is able to localize the area of the accessory pathway.
The patient underwent successful radiofrequency ablation of the WPW accessory pathway. A postablation ECG was performed and showed a normal PR interval and no evidence of a delta wave. She was discharged home on no cardiac medications with routine cardiology follow-up.
The image is a 3D representation of the right atrium. The blue-outlined "holes" delineate the area of the tricuspid valve. The color changes represent the earliest electrical activation that assists in localizing the area of the accessory pathway. The red dots indicate the ablation sites. AV = atrioventricular.
Image of a CARTO mapping system courtesy of Bradley C Clark, MD.
A 15-year-old male presents to the outpatient cardiology clinic with complaints of palpitations and syncope in association with exercise. He was playing soccer and passed out while chasing the ball. After being unconscious for a few minutes, he awoke with a full recollection of the event. He reported experiencing palpitations prior to passing out. He denies any symptoms at rest.
His physical examination in the clinic is normal, and his ECG is shown.
What are the ECG findings, and what is the next step in this patient's work-up?
Image courtesy of Bradley C Clark, MD.
Answer: The ECG, including QTc interval, is normal.
The next step in the work-up is obtaining an echocardiogram to evaluate for the coronary artery origins in the setting of exercise-induced syncope.
The patient's echocardiogram (shown) reveals a structurally normal heart with normal coronary artery origins and course. AV = aortic valve, LA = left atrium, LV = left ventricle, RA = right atrium, RV = right ventricle.
What is the next step in this patient's management?
Images courtesy of Bradley C Clark, MD.
Answer: The patient should undergo stress testing.
In those with exercise-induced syncope, an exercise cardiopulmonary stress test can help to recreate their symptoms as well as monitor for signs of arrhythmia and ischemic changes.[12]
The patient's rhythm during exercise stress testing is shown; he reported feelings of dizziness during the stress test.
What does the stress test show?
Image courtesy of Bradley C Clark, MD.
Answer: The stress test shows ventricular ectopy with degeneration into VT with a rate of approximately 250 bpm.
In a patient with a structurally normal heart and exercise-induced nonsustained VT, which of the following is the leading diagnosis?
Image courtesy of Bradley C Clark, MD. PVCs = premature ventricular contractions.
Answer: B. Catecholaminergic polymorphic VT (CPVT)
CPVT is an inherited arrhythmia disorder that is associated with life-threatening ventricular arrhythmias (VF and/or VT) in the setting of a structurally normal heart.[13,14] The arrhythmia is usually triggered by stress or exercise/activity.
There are two main gene mutations associated with CPVT, both found on chromosome 1, as follows[14,15]:
Adapted image of a human male karyotype on chromosome 1 courtesy of the National Human Genome Research Institute via Wikimedia Commons.
Defects in either the ryanodine receptor or calsequestrin gene lead to an increase in intracellular calcium during diastole.[16] In CPVT, there is increased activity of the sodium-calcium exchanger—which increases the resting membrane potential during diastole, potentially leading to delayed after-depolarizations.[17]
Image of a myocardiocyte courtesy of OCAL (OpenClipart) via Wikimedia Commons.
In the course of a normal cardiac action potential, a decrease in resting membrane potential occurs during diastole. Delayed after-depolarizations during the repolarization phase of the cardiac cycle can lead to ventricular arrhythmias; this is similar to the "R on T" phenomenon, in which there is ventricular depolarization (the R wave) of a ventricular ectopic beat on a preceding T wave (ie, an R wave is superimposed on a T wave).
Image of a cardiomyocyte action potential courtesy of Wikimedia Commons/Quasar. rect. = rectifier current/channel.
The treatment for CPVT includes medical, surgical, and device therapy.[13,14,18-21]
The 2013 expert consensus statement from the Heart Rhythm Society (HRS), the European Heart Rhythm Association (EHRA), and the Asia Pacific Heart Rhythm Society (APHRS) on the diagnosis and management of patients with inherited primary arrhythmia syndromes included the following treatment recommendations for those diagnosed with CPVT[21]:
Chest radiograph following ICD placement courtesy of Wikimedia Commons/Gregory Marcus, MD, MAS, FACC. The ICD generator is in the upper left chest, and the ICD lead is in the right ventricle. Note the two opaque coils along the ICD lead.
Only limited data exist, but it appears that there may be a benefit to catheter ablation in patients with CPVT. Specifically, it has been theorized that the ablation of bidirectional PVCs may prevent the triggering of ventricular arrhythmias.[22]
The image is a 3D reconstruction of the left ventricle. Ablation was performed in the apex of the left ventricle near the area of the anterolateral papillary muscle.
Image courtesy of Bradley C Clark, MD.
It is extremely important that all immediate family members of patients diagnosed with CPVT undergo testing for CPVT, especially if a mutation is discovered.
Beta blockers can be useful for asymptomatic carriers of a CPVT mutation, even if stress testing results have been negative (HRS/EHRA/APHRS class IIa recommendation).[21]
The American Heart Association (AHA) and American College of Cardiology (ACC) recommend that an athlete with CPVT and a history of symptoms or ventricular arrhythmias on exercise testing should be restricted from all competitive sports, except for class IA sports (eg, billiards, bowling, cricket, curling, golf, riflery[23]).[24]
Image of an autosomal dominant pedigree chart courtesy of Wikimedia Commons/Jerome Walker.
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