A 30-year-old man presented to the emergency department with palpitations and a heart rate over 200 beats per minute. He had a history of similar symptoms previously diagnosed as supraventricular tachycardia. Initial treatments including adenosine, cardioversion, metoprolol, and diltiazem slowed the heart rate but did not terminate the arrhythmia. The patient was diagnosed with idiopathic fascicular left ventricular tachycardia based on changes in QRS morphology and axis compared to sinus rhythm as well as evidence of AV dissociation. Verapamil was recommended as the next treatment as it specifically targets the calcium channels involved in this type of arrhythmia, unlike other treatments tried.

1. A Man With Incessant Narrow Complex Tachycardia
Esseim Sharma, MD; Michael Wu, MD
A 30-year-old man presented to the emergency department with palpitations and tachy-
cardia. He had been experiencing sore throat, fevers, and myalgias for the past day. He be-
came alarmed when he awoke from sleep with strong palpitations and a heart rate greater
than200/mindocumentedonhissmartwatch.Hehadsimilarsymptoms1yearagoandwas
diagnosed with and treated for supraventricular tachycardia (SVT). A subsequent outpa-
tient echocardiogram revealed a structurally normal heart; results of a follow-up electro-
cardiogram (ECG) were also normal (Figure 1, top).
On presentation to the emergency department, the patient’s temperature was 38.2°C;
blood pressure, 125/67 mm Hg; and pulse, 241/min. Physical examination was notable for an
erythematousoropharynx,tonsillarexudates,atachycardic,regularheartrhythm,andclear
lungs. An ECG was obtained (Figure 1, bottom). A modified Valsalva maneuver1
failed to con-
verttherhythm.Hewassubsequentlygivenaseriesofdosesofintravenousadenosine(6mg,
12mg,12mg),followedbydirectcurrentcardioversionat200J,whichconvertedtherhythm
to sinus for approximately 3 minutes. Intravenous metoprolol and intravenous diltiazem bo-
lus and drip were then administered, which slowed the heart rate but did not terminate the
arrhythmia. A rapid strep test result was positive, and he was given ampicillin.
Diagnosis
Idiopathic fascicular left ventricular tachycardia (IFLVT)
arising from the left anterior fascicle
What to Do Next
D. Stop diltiazem drip and administer intravenous verapamil
The differential diagnosis for this patient’s narrow-complex
tachycardia includes SVT, SVT with aberrancy, and IFLVT. The key
to the correct diagnosis is to differentiate IFLVT from SVT with or
withoutaberrancybyrecognizing3factors—changeinaxisfromsinus
rhythm; QRS morphology typical of IFLVT arising from the left an-
terior fascicle; and atrioventricular (AV) dissociation.
Figure1(top)showsthepatient’sbaselineECG,whichhasanor-
malQRSaxisanddurationof82ms.ThischangesinthenextECG,which
showsawiderQRSwithanincompleterightbundle-branchblock–like
morphology and a right inferior axis. This QRS morphology and axis
Figure 1. Patient’s baseline 12-lead electrocardiogram (top) and on presentation (bottom).
WHAT WOULD YOU DO NEXT?
A. Stop diltiazem drip and administer
intravenous amiodarone
B. Repeat synchronized direct
current cardioversion at 200 J
C. Switch to intravenous esmolol drip
D. Stop diltiazem drip and administer
intravenous verapamil
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2. istypicalofanIFLVTarisingfromtheleftanteriorfascicle.Unlikemost
ventriculartachycardias,theQRSdurationinIFLVTsisoftenonlyslightly
prolonged(around120ms),andthosearisingfromtheleftanteriorand
upperseptalfasciclescanevenbenarrow-complexwithQRSdurations
less than 110 ms, which adds to the diagnostic difficulty.
InSVTwithoutaberrancy,QRSmorphologyisnotchangedfrom
that during sinus rhythm. In contrast, both SVT with aberrancy and
IFLVTwillhaveabruptchangesinQRSmorphology.Onecanalsodif-
ferentiate IFLVT from SVT with aberrancy by looking for AV disso-
ciation,whichsuggestsaventricularoriginofarrhythmia.InAVdis-
sociation,atrialandventricularactivationareindependentfromeach
other,andtheventricularrateisfasterthantheatrialrate.Thisismore
notable when the ventricular rate has slowed and the noncon-
ducted P waves can be clearly seen (Figure 2).
IFLVTs are typically verapamil sensitive; therefore, administra-
tionofintravenousverapamilwouldbethenextbeststepinthispa-
tient with a structurally normal heart. Both amiodarone and intra-
venousesmololmayslowtheheartratebutaregenerallyineffective
atterminatingthearrhythmia.Repeatcardioversionwouldworkonly
temporarily, as the infection driving the IFLVT is still ongoing.
Discussion
Idiopathicventriculartachycardia(IVT)isaclassificationgiventoven-
tricular tachycardias that occur in the absence of structural heart dis-
ease and account for 10% of all ventricular tachycardias.2,3
IFLVT ac-
countsfor10%to15%ofIVTcases.4
IFLVTscanoriginatefromtheleft
posterior (≈90%), left anterior (5%-10%), or upper septal (rare) fas-
ciclesandbehaveasreentranttachycardias.5
IFLVTstypicallyoccurin
adults aged 15 to 40 years (usually male [60%-80%]) and are often
triggeredbyexternalstressors.6,7
Inthispatient,anupperrespiratory
tract infection was likely the stressor. IFLVT is often misdiagnosed as
SVT with or without aberrancy because of the young age of presen-
tation and frequent lack of hemodynamic compromise.8
IFLVTs,unlikethemajorityofIVTs,areclassicallysensitivetover-
apamil because of its effect on the slow inward calcium channel,
whichisthoughttobecriticaltothepropagationofthearrhythmia.5,9
Intravenousadenosine,electricalcardioversion,andβ-blockersare
largely ineffective at terminating IFLVT because of lack of effect on
the slow inward calcium channel. Diltiazem can sometimes be ef-
fective in suppressing IFLVT, as it also effects this calcium channel,
althoughithasdifferentbindingsitesthanverapamil.10
Therehave
been no studies examining the 2 drugs head-to-head. Anecdotally,
verapamil seems to be more effective in terminating IFLVT acutely
andisconsideredfirst-linetreatment.4
Importantly,intravenousnon-
dihydropyridines should only be used in patients with structurally
normal hearts, as they can lead to hemodynamic instability due to
negative inotropy. Over the long term, oral verapamil (usually
240-480 mg once daily) may fail to adequately suppress the ar-
rhythmia; catheter ablation is then recommended. Because syn-
cope and sudden death are rare in these patients, routine place-
ment of an implantable cardiac defibrillator is not necessary.5
Patient Outcome
Thepatientreceivedintravenousverapamilwithresolutionofhisar-
rhythmia. He has received maintenance oral verapamil, with no re-
currences over 6 months.
ARTICLE INFORMATION
Author Affiliations: Brown University, Providence,
Rhode Island.
Corresponding Author: Michael Wu, MD, Rhode
Island Hospital, 593 Eddy St, APC 814, Providence,
RI 02903 (michael.wu@lifespan.org).
Published Online: October 25, 2019.
doi:10.1001/jama.2019.16560
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient for
providing permission to share his information.
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Figure 2. Patient’s 12-lead electrocardiogram after
receipt of adenosine, metoprolol, and diltiazem.
The ventricular rate has slowed from initial
presentation (Figure 1, bottom). Arrowheads
indicate nonconducted P waves.
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