Pulseless ventricular tachycardia overview

# Overview
Pulseless ventricular tachycardia is an often fatal cardiac dysrhythmia where the regular rhythmic contraction of the heart is replaced by non-rhythmic, faster, yet inadequate contractions. In 1906 Gallavardin discovered the reasons behind the cardiac instability which leads to ventricular tachycardia, and put forth the idea that VT could convert into ventricular fibrillation, pulselessness and sudden death. In 1909,Thomas Lewis gave the first electrocardiographic description of ventricular tachycardia. It was also first implied in 1921 that coronary occlusion could be the main incriminating factor of any ventricular tachycardia. The ineffective contractions in pulseless ventricular tachycardia do not appropriately perfuse the organ, leading to ischemia as well as heart failure. This condition requires immediate medical attention as it is an emergency and can lead to ventricular fibrillation and sudden death.
As a result of markedly rapid ventricular contractions, diastole is shortened and there is a significant decrease in the ventricular filling. This results in a significant reduction in cardiac output, and an absent pulse. Pulseless ventricular tachycardia refers to a rhythm with a heart rate above 120 beats per minute, wide QRS complexes above 120 milliseconds, the dissociation between the atria and ventricles, presence of fusion beats, and an electrical axis between -90 to -180. Because the majority of wide complex tachycardia cases will be ventricular tachycardia, any wide complex tachycardia should always be assumed to be due to ventricular tachycardia until proven otherwise.

# Historical Perspective
There is limited information about the historical perspective of Pulseless ventricular tachycardia.

# Classification
Pulseless ventricular tachycardia as a ventricular tachycardia may be classified based on the morphology of the QRS complexes into two subtypes/groups: monomorphic ventricular tachycardia, and polymorphic ventricular tachycardia.

# Pathophysiology
Rapid abnormal automaticity and triggered activity are thought to be the main electrophysiological mechanisms of pulseless ventricular tachycardia.

# Causes
Structural heart disease is the most common cause of pulseless ventricular tachycardia. Other causes include but are not limited to,  drugs/medications, congenital heart diseases, not to mention congenital and inherited channelopathies. It is important to note that QT interval lengthening medications, as well as electrolyte disturbances, can also result in pulseless ventricular tachycardia.

# Differentiating pulseless ventricular tachycardia from Other Diseases
Pulseless ventricular tachycardia must be differentiated from other diseases that cause wide complex tachycardia, such as supraventricular tachycardia with aberrant conduction, SVT with pre-excitation and antidromic atrioventricular reentrant tachycardia

# Epidemiology and Demographics
Ventricular tachycardia and ventricular fibrillation are the causes of most sudden cardiac deaths and account for about 300,000 deaths per year in the united states alone. This figure is most likely underestimated as it doesn't account for deaths due to unwitnessed dysrhythmias. The majority of deaths due to ventricular arrhythmias occur In adults over 35 years of age.

# Risk Factors
Risk factors for pulseless ventricular tachycardia as a cause of wide complex tachycardia includes any disease or condition that stresses or damages myocardial tissue. A family history of ventricular tachycardia or other rhythm disturbances may increase risk, while some lifestyle changes or medications may decrease risk.

# Screening
According to the 2017 American Heart Association guidelines screening of first-degree relatives is recommended when a patient presents with any of the symptoms or has a positive family history of conditions like QT syndrome, hypertrophic, dilated cardiomyopathy and right ventricular dysplasia.

# Natural History, Complications, and Prognosis
On initial presentation, patients with impending pulseless ventricular tachycardia may show signs of inadequate cardiac perfusion such as chest pain, shortness of breath, diaphoresis, palpitations, and syncope. Physical examination may be positive for hypotension, tachycardia, tachypnea, increased JVD, and an S1. Eventually, Pulseless ventricular tachycardia ensues and patients become unconscious and unresponsive with no detectable pulse. If defibrillation is not begun as soon as possible patients may progress to cardiac arrest and death.

# Diagnosis

## Diagnostic Study of Choice
The diagnosis of pulseless ventricular tachycardia is based on ECG and physical examination findings. An ECG should be the initial study, and other investigations may be carried out afterward to determine the underlying etiology.

## History and Symptoms
Pulseless ventricular tachycardia may be symptomatic or asymptomatic. In a young patient with a family history of sudden death, immediate evaluation for an inherited ventricular syndrome is recommended. If symptomatic, the ventricular rate, duration of tachycardia, and the presence of underlying disease determine the kind of symptoms that present.

## Physical Examination
Physical examination should consist of a thorough cardiac exam, lung exam, and close monitoring of vital signs. Physical examination may be positive for hypotension, tachycardia, tachypnea, increased JVD, and an S1.

## Laboratory Findings
There aren't any specific findings associated with pulseless ventricular tachycardia. However, investigations such as serial cardiac enzymes, serum electrolytes, and toxicology screen should be conducted to find the underlying etiology of the arrhythmia.

## Electrocardiogram
An ECG is very helpful in the diagnosis of Pulseless ventricular tachycardia. Findings on an ECG suggestive or diagnostic of Pulseless ventricular tachycardia include regular R-R intervals, rapid ventricular rate with an indistinguishable atrial rate (absence of p-waves), Av dissociation, and a wide QRS complex (more 0.12 sec).

## X-ray
There are no x-ray findings associated with Pulseless ventricular tachycardia.

## Echocardiography
There are no specific echocardiography/ultrasound findings associated with pulseless ventricular tachycardia. However, echocardiography/ultrasound may be helpful in the evaluation of underlying etiologies in patients as well as complications due to the arrhythmia.

## Cardiac MRI
There are no specific MRI findings associated with pulseless ventricular tachycardia. However, a cardiac MRI may be helpful when structural heart disease is implicated as an etiology and the assessment provided by echocardiography is not satisfactory. A cardiac MRI is particularly helpful in the evaluation of structural heart disease i.e arrhythmogenic right ventricular cardiomyopathy as well it's infiltrative diseases such as sarcoidosis.

## Other Diagnostic Studies
2017 guidelines from the AHA/ACC/HRS state that MRI, cardiac computed tomography (CT), or radionuclide angiography can be useful in detecting and characterizing underlying heart disease when echocardiography fails to provide an accurate evaluation of LV or RV function and/or assessment of structural changes. Electrophysiologic (EP) testing can be useful when an uncertain diagnosis of sustained monomorphic ventricular tachycardia. An electrophysiological study is especially useful for assessing the risk of ventricular tachycardia in patients with ischemic cardiomyopathy, non-ischemic cardiomyopathy, or adult congenital heart disease who have syncope or other ventricular arrhythmia symptoms and who do not meet indications for a primary prevention implantable cardioverter-defibrillator.

# Treatment

## Medical Therapy
Medical therapy with IV vasopressors and antiarrhythmic medications i.e amiodarone, is usually simultaneous with defibrillation. 1mg 1V of epinephrine administered every 3-5 minutes or, a single dose of 40 units IV of vasopressin can be used as vasopressors.

## Interventions
Immediate defibrillation is the main intervention for pulseless ventricular tachycardia.

## Surgery
Surgery is not a mainstay or a preferred method of treatment for pulseless ventricular tachycardia.

## Primary Prevention
Implantable cardiac defibrillators are recommended in high-risk patients i.e, patients with dilated cardiomyopathy for the primary prevention of pulseless ventricular tachycardia.

## Secondary Prevention