A systematic search of the medical literature was performed on
January 9, 2008. The search, limited to human subjects and English
language journals, included the National Guideline Clearinghouse,
the Cochrane database, PubMed, UpToDate®, and
PIER. The current American College of Cardiology (ACC)/American
Heart Association (AHA)/European Society of Cardiology
2006 Guidelines for Management of Patients with Ventricular Arrhythmias
and the Prevention of Sudden Cardiac Death, and the Management of Patients
with Supraventricular Arrhythmias can be found at www.acc.org
Cardiac arrhythmia is an abnormality of impulse generation, impulse
propagation, or a combination of both. Although arrhythmias can
occur in all age groups, significant rhythm disturbances are relatively
uncommon in young, healthy individuals. The primary purposes of
the history in evaluating a cardiac arrhythmia are to determine
the underlying etiology, anatomic abnormalities, physiologic disturbances,
cardiac status, and prognosis.
The symptoms associated with cardiac arrhythmias vary widely.
They may be very minor such as an awareness of the heartbeat (palpitations).
More serious symptoms usually reflect a decrease in cardiac output
resulting from reduced ventricular filling during the tachycardia.
Patients may describe a rapid, sustained heartbeat that may be regular
or irregular, or may describe intermittent accelerations or decelerations
of the heartbeat. Some patients are able to detect even slight variations
in the heart rate or rhythm while others may have no awareness of
any arrhythmia—even ventricular tachycardia (VT). Patients
will commonly seek medical attention because of palpitations, presyncope,
syncope, or symptoms of angina or heart failure.
Wide QRS complexes result from impulses that have at least some
conduction outside the normal conduction system. By definition,
wide-complex tachycardias have a rate greater than 100 beats per
minute and have a QRS duration greater than or equal to 120 ms.
VT is one form of a wide-QRS-complex tachycardia, but a wide QRS
complex may also occur in supraventricular tachycardia (SVT) when
there is a conduction delay in the His–Purkinje system
or there is conduction over a parallel route from the atria to the
ventricle, that is, an accessory pathway. In general, the wider
the QRS complex, the more likely the rhythm is to be ventricular
in origin, especially when the complexes are greater than 160 ms
in duration.1 The patient’s age and risk factors
play a significant role in general as to the potential etiology
of a wide complex rhythm. Other evidences to support the diagnosis
of VT include the independent P-wave activity, fusion beats, AV
dissociation, and concordance throughout the precordial leads. The
absence of an RS complex in all precordial leads, or an RS interval
of more than 100 ms, is indicative of VT.2 If the origin
of the wide-complex tachycardia cannot be determined, the safest
option is to treat it as VT.
Narrow-complex tachyarrhythmias almost always have a supraventricular