Ventricular Tachycardia Workup

Updated: Dec 31, 2015
  • Author: Steven J Compton, MD, FACC, FACP, FHRS; Chief Editor: Jeffrey N Rottman, MD  more...
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Workup

Approach Considerations

Electrocardiography (ECG) is the criterion standard for the diagnosis of ventricular tachycardia (VT). In a patient who is hemodynamically unstable or unconscious, however, the diagnosis of VT is made from the physical findings and ECG rhythm strip only.

Advanced cardiac life support (ACLS) protocols should be quickly followed. Laboratory tests should be deferred until electrical cardioversion has restored sinus rhythm and the patient is stabilized.

A guideline from the American College of Cardiology (ACC), the American Heart Association (AHA), and the European Society of Cardiology (ESC) recommends direct current (DC) cardioversion with sedation at any time during treatment in patients thought to have sustained monomorphic VT with hemodynamic compromise. [25] If the patient is hemodynamically stable at presentation, a 12-lead ECG and electrolyte levels may be obtained before attempted conversion with medications or DC cardioversion.

The ECG should be repeated once sinus rhythm has been restored, or when prior VT is suspected, as in a patient who experienced syncope. The ECG may also provide clues for differentiating among potential arrhythmia mechanisms or causes of VT, such as the following:

  • Acute or chronic infarction
  • Ischemia
  • Myocardial scar
  • Ventricular preexcitation
  • Hypertrophy
  • Conduction disease
  • QT prolongation
  • Other precordial repolarization abnormalities (eg, Brugada syndrome and arrhythmogenic right ventricular dysplasia [ARVD])

Appropriate laboratory studies are indicated. In addition, a full evaluation should usually include echocardiography and coronary angiography to assess for structural and ischemic heart disease. These considerations are paramount in defining further treatment in any patient with VT. These patients often require aggressive management of underlying ischemic heart disease and heart failure.

Screening of first-degree relatives should be contemplated when a patient is identified as having any of the following:

  • Long QT syndrome
  • Short QT syndrome
  • Hypertrophic or dilated cardiomyopathy
  • Right ventricular dysplasia

Family screening typically involves the following:

  • History and physical examination
  • ECG
  • Echocardiography
  • Treadmill testing

In some patients with spontaneous polymorphic VT, genetic studies may be helpful for family screening or for clarifying a diagnosis. Spontaneous polymorphic VT may be related to genetic mutations affecting ion channels, such as occur in long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic VT. Finally, some patients are predisposed to drug-induced ventricular arrhythmias by otherwise subclinical genetic ion channel defects.

Chest radiography is indicated if symptoms suggest the possibility of heart failure or other cardiopulmonary pathology as a contributing factor. Cardiac computed tomography (CT) and cardiac magnetic resonance imaging (MRI) are evolving quickly but have not yet supplanted echocardiography and nuclear imaging for quantification of ventricular function. Cardiac MRI can be especially helpful in the evaluation of uncommon myocardial infiltrative diseases, such as sarcoidosis.

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Laboratory Studies

Assess electrolyte levels of all patients with VT, including serum potassium, magnesium, calcium, and phosphate levels. Ionized calcium levels are preferred to total serum calcium levels. Hypokalemia is a common VT trigger and is commonly seen in patients taking diuretics. Hypokalemia, hypomagnesemia, and hypocalcemia may predispose patients to either monomorphic VT or torsades de pointes.

In accordance with the clinical history, measure serum levels of therapeutic drugs (eg, digoxin and tricyclic antidepressants). Toxicology screens (eg, for methamphetamine or cocaine) may be helpful in cases related to recreational drug use.

Evaluate for myocardial ischemia or infarction with serum cardiac troponin I or T levels or other cardiac markers if symptoms or clinical signs of ischemia are present. Persistently elevated cardiac enzyme levels may also be an indication of ongoing myocarditis.

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Electrocardiography

Polymorphic ventricular tachycardia

When the QRS complex varies from beat to beat, the rhythm is described as polymorphic VT and suggests a variable electrical activation sequence. The most notorious, and probably the most common, form of polymorphic VT is torsades de pointes. The disorder’s name is a French term meaning “twisting of the points” and refers to the unusual shifting-axis QRS complexes that appear as if the heart is rotating upon an axis.

Torsades de pointes typically occurs during sinus rhythm and in the presence of drugs or conditions that prolong the QT interval (eg, class IA antiarrhythmics, hypomagnesemia, and droperidol). The dysrhythmia may occur either in the presence or in the absence of myocardial ischemia or infarction. The term torsades de pointes is reserved for polymorphic VT observed in the setting of a prolonged QT interval (see the images below). Other polymorphic VTs are occasionally observed during ischemia or myocarditis.

 Torsades de pointes. 

Image A: This is polymor Torsades de pointes. Image A: This is polymorphic ventricular tachycardia associated with resting QT-interval prolongation. In this case, it was caused by class III antiarrhythmic agent sotalol. This rhythm is also observed in families with mutations affecting certain cardiac ion channels. Image B: Torsades de pointes, a form of ventricular tachycardia. Courtesy of Science Source/BSIP.
Torsades de pointes. Torsades de pointes.

Monomorphic ventricular tachycardia

When the ventricular activation sequence is constant, the ECG pattern remains the same, and the rhythm is called monomorphic VT (see the image below). Monomorphic VT is most commonly seen in patients with underlying structural heart disease. There is typically a zone of slow conduction, most commonly the result of scarring or fibrillar disarray. Causes include prior infarct, any primary cardiomyopathy, surgical scar, hypertrophy, and muscle degeneration.

Monomorphic ventricular tachycardia. Monomorphic ventricular tachycardia.

Reentrant tachycardias occur when an electrical wavefront travels slowly through the zone of slow conduction (usually damaged muscle protected by scar tissue), allowing the rest of the circuit time to repolarize. The wavefront breaks out of the scar, activates the ventricle, and reenters the slow conduction zone.

Monomorphic VT is occasionally observed in patients with structurally normal hearts (idiopathic VT). These VTs are often exercise-dependent, and their clinical behavior may be more consistent with triggered activity or abnormal automaticity.

Monomorphic VTs are typically named for their site of origin. The following are the most commonly involved sites [29] :

  • Right ventricular outflow tract
  • Left ventricular outflow tract
  • Left ventricular septum
  • Aortic root

The QRS morphology during VT can be used to predict the exit site from the zone of slow conduction [30] or the site of origin, regardless of the underlying substrate. Earliest activation is closest to the leads with QS complexes during tachycardia. [31]

Monomorphic VTs have classically been considered benign. Rarely, however, they may result in sudden death, despite the presence of a structurally normal heart. [32]

Differentiating monomorphic ventricular tachycardia from supraventricular tachycardia

Polymorphic VT is easily diagnosed after exclusion of lead motion artifact. Monomorphic VT can be more difficult to sort out. The ECG will demonstrate a wide-complex tachycardia, representing either VT or supraventricular tachycardia (SVT) with aberrant conduction. If the patient is unstable, or if differentiation between VT and SVT is uncertain, treat the rhythm as VT; the majority of patients with wide-complex regular tachycardias will have VT. If the patient is stable, the ECG can be examined for clues to the mechanism underlying the arrhythmia.

Atrioventricular dissociation

AV dissociation (see the images below), is apparent in approximately half of VT episodes. When present, it is a hallmark of VT. [33] It occurs because the sinus node is depolarizing the atria at a rate that is slower than the pathologic, faster ventricular rate. P waves can be seen at times in between or embedded in the QRS complexes, but the P waves and QRS complexes have their own independent rates.

ECG shows form of idiopathic ventricular tachycard ECG shows form of idiopathic ventricular tachycardia (VT) seen in absence of structural heart disease. This rhythm arises from left ventricular septum and often responds to verapamil. Upon superficial examination, it appears to be supraventricular tachycardia with bifascicular conduction block. Closer examination of lead V1 shows narrowing of fourth QRS complex, consistent with fusion between wide QRS complex and conducted atrial beat, confirming atrioventricular dissociation and VT mechanism.
Atrioventricular dissociation. Atrioventricular dissociation.

Retrograde conduction can also exist from the ventricles to the atria via the AV node. This is not AV dissociation and reveals itself on ECG as a 1:1 correlation between the wide QRS complex and an inverted P wave, which follows the QRS complex.

Fusion and capture beats

Fusion beats and capture beats can occur in the presence of VT, depending on the refractory period of the AV node and on the timing of ventricular and atrial depolarizations, respectively (see the image below). If present, they help distinguish VT from SVT with aberrant conduction.

Fusion beats, capture beats, and atrioventricular Fusion beats, capture beats, and atrioventricular dissociation.

A fusion beat has a mixed morphology because of normal AV node/His-Purkinje conduction occurring simultaneously with abnormal ventricular depolarization. A normally conducted impulse travels from the AV node through the normal conduction pathway (producing a narrow QRS complex), and the competing impulse originates from the abnormal ectopic ventricular focus outside of the normal conduction pathway (producing a wide QRS complex). The 2 impulses converge, leading to a mixed (fused) QRS.

A capture beat occurs when an atrial impulse arrives at the AV node when the node has just recovered from its refractory period. The timing must be just right, because the AV node is frequently in its refractory state as a result of depolarization caused by retrograde conduction from the rapid ventricular rhythm. When this occurs, conduction proceeds normally through the AV node/His-Purkinje system, “capturing” the ventricle and leading to a normal, narrow QRS complex.

Unfortunately, most VT tracings do not show obvious clues of AV dissociation, fusion, or capture. In such cases, the QRS morphology usually provides enough information to permit an accurate diagnosis. The 2 best sets of ECG criteria are described below.

Brugada et al [4] proposed ECG discrimination criteria for VT that focused primarily on the QRS morphologies in the precordial leads (V1-V6). They reported a sensitivity of 98.7% and a specificity of 96.5% with the following criteria:

  • Absence of RS complexes in the precordial leads
  • RS duration exceeding 100 ms in any precordial lead
  • Ventriculoatrial dissociation in any of 12 leads
  • Certain QRS morphologies, such as QR or QS in V6

Vereckei et al [5] refined a different ECG algorithm based on a single lead, aVR, and reported better accuracy than was achieved with the Brugada criteria. They noted the presence of a negative QRS complex in aVR during right or left bundle-branch conduction of SVTs. VT was predicted by the following:

  • Presence of an initial R wave in aVR
  • Width of an initial r or q wave exceeding 40 ms in aVR
  • Notching on the initial downstroke of a predominantly negative QRS complex in aVR
  • Ventricular activation-velocity ratio (V i/V t) less than or equal to 1

Differentiating ventricular tachycardia from sinus tachycardia

The image below demonstrates a tachycardia with a 1:1 atrial-to-ventricular ratio. It is not immediately clear whether the atria are driving the ventricles (sinus tachycardia) or the ventricles are driving the atria (VT).

ECG from 32-year-old woman with recent-onset heart ECG from 32-year-old woman with recent-onset heart failure and syncope.

In this case, a diagnosis of sinus tachycardia would require the presence of severe conduction disease manifesting as marked first-degree AV block with left bundle-branch block. Close inspection shows, however, that the actual diagnosis is VT, as indicated by absence of RS complexes in the precordial leads, a QS pattern in V6, and an R wave in aVR. The patient proved to have an incessant VT associated with dilated cardiomyopathy.

Signal-averaged ECG

Signal-averaged ECG (SAECG) is a noninvasive test that often demonstrates abnormal results in patients with VT related to prior infarct or right ventricular dysplasia. ACC/AHA/ESC guidelines suggest that SAECG—along with heart rate variability (HRV), baroflex sensitivity, and heart rate turbulence—may be useful for refining the diagnosis and risk stratification of patients with ventricular arrhythmias or those who are at increased risk of developing life-threatening ventricular arrhythmias. [25]

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Echocardiography

ACC/AHA/ESC guidelines recommend the use of echocardiography for patients at high risk for serious ventricular arrhythmias or sudden cardiac death. This group consists of patients with any of the following [25] :

  • Dilated, hypertrophic, or right ventricular cardiomyopathy
  • A history of acute myocardial infarction
  • Inherited disorders associated with sudden cardiac death
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Cardiac Imaging Studies

Cardiac CT and cardiac MRI are evolving quickly but have not yet supplanted echo and nuclear imaging for quantification of ventricular function. Cardiac MRI can be especially helpful in the evaluation of uncommon myocardial infiltrative diseases, such as sarcoidosis.

Although cardiac MRI is often used for the evaluation of ARVD, the diagnostic yield of this test has yet to be clearly defined. Right ventricular angiography may still be the criterion standard imaging study for this disorder.

The ACC/AHA/ESC guidelines state that MRI, cardiac CT, or radionuclide angiography can be useful in patients with ventricular arrhythmias when echocardiography fails to provide accurate evaluation of left or right ventricular function. [25] These studies may also be useful for assessment of structural changes in the heart. [25]

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Assessment of Recurrent Syncope or Palpitations

Occasionally, patients present with recurrent syncope or palpitations. In this setting, an arrhythmic cause of syncope may be sought. Options include Holter monitoring, which has a low yield, and event recording. The goal is to document the patient’s rhythm during symptoms. Patients with infrequent symptoms are best served by implantation of a loop recorder, which may have a battery life of 2-4 years.

If those techniques are not practical, a provocative electrophysiologic study (EPS) can be performed. The 2006 ACC/AHA/ESC guidelines recommend electrophysiologic evaluation in patients with syncope of unknown etiology with impaired left ventricular function or structural heart disease. [25]

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Genetic Testing

Genetic testing is now feasible for a variety of inherited disorders that may cause long QT syndrome, ARVD, or dilated or hypertrophic cardiomyopathy. However, the absence of a defined genomic mutation does not exclude these abnormalities; the current approach is not exhaustive and is focused on established monogenic germline abnormalities.

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Myocardial Biopsy

The advent of cardiac MRI has facilitated the diagnosis of infiltrative cardiomyopathies, but occasionally, myocardial biopsy with special histologic processing may be useful in the diagnosis of ARVD or a hypertrophic or infiltrative myopathy. Most reentrant VTs are related to myocardial scarring from ischemic or dilated cardiomyopathy. Fibrotic replacement of myocytes and interweaving of scar tissue with functional myocytes is common along slow conduction zones of VT circuits.

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Pacemaker and Other Cardiac Devices

The presence of a dual-chamber pacemaker or implantable cardioverter-defibrillator (ICD) can occasionally simplify diagnosis. Most contemporary devices are capable of recording and logging tachyarrhythmias for subsequent analysis during interrogation of the implanted device.

Analysis may reveal the disease process underlying the VT. On the other hand, the episode may prove to have been triggered by the device itself. Possibilities include the following:

  • Tracking of an atrial tachyarrhythmia in a dual-mode, dual-pacing, dual-sensing (DDD) device or an atrial-triggered, ventricular-inhibited (VDD) device
  • Endless loop tachycardia
  • Inappropriate rate-responsive pacing due to sensor problems or incorrect sensor programming
  • Overt pacemaker failure (runaway pacer)

The most common problem involves the patient whose device is tracking atrial fibrillation (AF) or flutter. In the absence of a mode-switching algorithm, a VDD or DDD pacer responds by pacing the ventricle at the programmed upper rate limit of the device. Application of a magnet to the pacer generator may terminate endless loop tachycardia or drop the paced rate enough to allow diagnosis of the underlying atrial tachyarrhythmia.

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Electrophysiologic Study

Diagnostic EPS requires placement of electrode catheters in the ventricle, followed by programmed ventricular stimulation using progressive pacing protocols. Premature ventricular beats [34] are induced after conditioning pacing drives in an attempt to induce reentrant arrhythmia.

In patients with symptoms suggestive of VT, this kind of provocative testing can be used to assess whether the ventricles can sustain a reentrant tachyarrhythmia. The diagnostic yield of EPS is highest in patients with reentrant VT circuits.

EPS is particularly relevant in patients considered to be at high risk for sudden death due to significant underlying structural heart disease. EPS may be useful in demonstrating whether the substrate for sustained VT is present in a patient presenting with syncope or ischemic, nonsustained VT. In patients with recurrent symptoms related to VT, programmed electrical stimulation can generally reproduce clinically relevant VT circuits.

If the diagnosis of right ventricular dysplasia is being considered, many laboratories perform right ventricular angiography at the time of the EPS. Diagnostic abnormalities include right ventricular dilation, dyskinesis, and aneurysms.

In accordance with the ACC/AHA/ESC guidelines, EPS is recommended for diagnostic assessment of patients with a remote history of myocardial infarction and symptoms related to ventricular tachyarrhythmias, including palpitations, presyncope, and syncope, and in patients with coronary heart disease to guide and measure the efficacy of VT ablation. The ACC/AHA/ESC guidelines state that EPS is reasonable for diagnostic evaluation in patients with palpitations or suspected outflow tract VT. [25]

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