The 12-Lead Electrocardiogram
in Supraventricular Tachycardia
Uday N. Kumar, MD, Rajni K. Rao, MD,
Melvin M. Scheinman, MD*
Division of Cardiology, Department of Medicine, 500 Parnassus Avenue, Box 1354, University of California,
San Francisco, San Francisco, California 94143, USA
The term supraventricular tachycardia (SVT)
encompasses a range of common arrhythmias in
which the atrial or atrioventricular (AV) node is
essential for the perpetuation of the tachyarrhyth-
mia . Because of misdiagnosis and inconsistent
classification, the exact prevalence of SVT is not
clear but may be as high as six to eight per 1000
people in the United States . SVT affects pa-
tients of varied ages, often can lead to symptoms,
and may occur in patients with or without struc-
tural heart disease.
The diagnosis of SVT is made primarily by
using the 12-lead electrocardiogram (ECG). Cor-
rect ECG diagnosis of SVT is important for
several reasons. First, because symptomatic pa-
tients who may have SVT often require rapid and
accurate treatment, misidentification of the type
of SVT can lead to inappropriate acute manage-
ment. Second, making the correct ECG diagnosis
of the type of SVT is important for long-term
prognosis and treatment strategies, including the
selection of effective medications or the decision to
refer a patient for catheter ablation. Finally, for
patients who do go on to catheter ablation,
a correct ECG diagnosis of the type of SVT
facilitates the appropriate choice of ablation strat-
egy.The correct choiceis essentialbecause the risk,
duration, complexity, and success rate of catheter
ablation varies based on the type of SVT .
Despite its importance, making the correct
ECG diagnosis of SVT type may be difficult for
numerous reasons. First, during the acute care of
highly symptomatic or unstable patients who have
possible SVT, the health care provider may be
pressed for time. Second, the correct diagnosis
may also be elusive when only a rhythm strip (as
opposed to a 12-lead ECG) is available. Similarly,
SVT may be suspected in hospitalized patients
who are monitored on telemetry, but such mon-
itoring equipment may not be able to generate
a true 12-lead ECG. Third, the ECG morphology
may be more unusual in patients taking antiar-
rhythmic medications or in patients who have had
prior ablation or surgical procedures. For in-
stance, patients who have congenital heart disease
develop SVT as a late complication [4,5]. Fourth,
variability in the placement of ECG electrodes
may affect the ECG tracing. Finally, the ECG
computer diagnosis of arrhythmias is unreliable.
These potential difficulties represent just a few of
the challenges to accurate ECG diagnosis of SVT.
This article provides a stepwise approach to
the 12-lead ECG diagnosis of SVT. It first
presents an initial approach to categorization
and diagnosis. Then, the common ECG manifes-
tations of each type of SVT are discussed in-
algorithm for diagnosing suspected SVT based
on the ECG.
The various forms of SVT include sinus tachy-
cardia (ST), focal atrial tachycardia (AT), multifo-
cal atrial tachycardia (MAT), atrial fibrillation
(AF), atrial flutter (AFl), AV node reentrant
* Corresponding author.
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Cardiol Clin 24 (2006) 427–437
tachycardia (AVNRT), AV reentrant tachycardia
(AVRT), junctional tachycardia (JT), and perma-
nent junctional reciprocating tachycardia (PJRT).
The first step in diagnosing SVT is to catego-
rize the rhythm as narrow complex (QRS ! 120
milliseconds) or wide complex (QRS R 120
milliseconds) and as regular (fixed R-R cycle
lengths) or irregular (variable R-R cycle lengths)
(Table 1). Some tachycardias are represented in
more than one category. The next step is to look
for evidence of atrial activity. If a discrete P
wave is visible, the relationship of the P wave to
the QRS complex should be evaluated. This rela-
tionship is characterized as either a ‘‘short-RP
tachycardia’’ or a ‘‘long-RP tachycardia.’’ In
short-RP tachycardia, the time from the P wave
to the preceding R wave is less than the time
from the P wave to the following R wave (RP !
PR). In long-RP tachycardia, the opposite is true
(RP O PR) (see Table 1).
In addition to cycle regularity and QRS width,
the following ECG criteria may help differentiate
the various types of SVT: heart rate during
tachycardia; mechanism of initiation/termination;
P wave/QRS/ST morphology; changes in cycle
length with the appearance of bundle-branch
block; and ECG changes in response to maneu-
vers such as carotid sinus massage or adenosine
administration. One study reports that viewing
the ECG at both normal (25 mm/s) and faster
(50 mm/s) paper speeds may improve diagnostic
accuracy . The findings and criteria helpful in
the diagnosis of each particular SVT are discussed
in greater detail later.
ST is a long-RP tachycardia that presents with
a heart rate over 100 beats/min (bpm). The
P wave morphology is identical to that of normal
sinus rhythm. There usually is a gradual onset and
termination that often can be appreciated on
Holter or telemetry monitoring. A variant of ST,
sinus node reentrant tachycardia, comprises a re-
entrant loop originating in the sinus node, behaves
clinically like an SVT, and has a sudden onset and
abrupt termination. In sinus node reentry tachy-
cardia, the PR interval during tachycardia may
differ from normal sinus rhythm, although the
P wave morphology is identical. True sinus node
reentrant tachycardia seems to be uncommon,
with most of the reported cases originating from
high in the crista terminalis . Patients who have
another variant of ST, termed ‘‘inappropriate si-
nus tachycardia,’’ show persistent tachycardia
during the day with marked increases in heart
rate in response to exercise. This diagnosis is
made from the 24-hour Holter recording, and
beta-blockers are the drugs of choice.
Initial categorization of tachycardic rhythms using the 12-lead electrocardiogram
Typical (slow-fast) AVNRT
Atypical (slow-slow) AVNRT (usually)
AT (less commonly)
Atypical (fast-slow) AVNRT
Orthodromic AVRT (slowly conducting
AT (more commonly)
AFl (fixed AV block)
AFl (variable AV block)
ST, JT, AT, AVNRT, orthodromic AVRT,
or AFl with aberrancy
Monomorphic ventricular tachycardia
Irregular AF, AFl, or MAT with aberrancy
AF, AFl with pre-excitation
Polymorphic ventricular tachycardia
Abbreviations: AF, atrial fibrillation; AFl, atrial flutter; AT, atrial tachycardia; AVNRT, atrioventricular node reen-
trant tachycardia; AVRT, atrioventricular reentrant tachycardia; JT, junctional tachycardia; MAT, multifocal atrial
tachycardia; PJRT, permanent junctional reciprocating tachycardia; ST, sinus tachycardia.
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THE 12-LEAD ECG IN SUPRAVENTRICULAR TACHYCARDIA