Paroxysmal ventricular tachycardia is a rhythm abnormality characterized by a series of ventricular contractions originating from one or more ventricular loci, at a rate greater than 100-120 beats/minute. The tachycardia is considered to be nonsustained if it lasts for less than 30 seconds, or sustained if the duration is longer.
The typical presentation of ventricular tachycardia (VT) is represented by palpitations. If there is cardiovascular compromise then symptoms are much more severe and consist of vertigo, syncope, chest pain, dyspnea due to decreased cerebral and myocardial irrigation or venous pulmonary hypertension. The term "paroxysmal" entails that the beginning and the end of the episode occur abruptly.
Patients with personal or familial history of sudden death should be evaluated for long and short QT syndromes, Brugada syndrome, arrhythmogenic right ventricular dysplasia and catecholaminergic polymorphic VT  , as family history of these diseases may indicate that the condition is present in the examined patient  .
If there is a loss of consciousness in the supine position or the patient has no aura, then the patient should be evaluated for VT, as vasovagal syncope usually appears in other contexts . It is also important to determine what medication the patient is taking since certain drugs are known to have proarrhythmic effects.
Physical examination findings depend on whether the evaluation is performed during the crisis or between episodes. During the interval between episodes, patients may show signs of structural heart conditions such as murmurs or other pathological features of decompensated heart disease. During the VT episode, patients are tachycardic, possibly tachypneic and may either be anxious, lethargic or comatose, depending on the cerebral perfusion and blood pressure. Diminished peripheral perfusion manifests as pallor and diaphoresis.
The main tool that establishes the diagnosis of ventricular tachycardia is electrocardiography. The arrhythmia may be monomorphic or polymorphic, depending on the number of hyperexcitable loci, commonly located in the ventricular outflow tracts, aortic root or left ventricular septum . When VT occurs in a patient with long QT syndrome, this entity is called "torsade de pointes" and has a particular morphology. Reentrant tachycardia has a structural substrate, most commonly consisting of scar tissue and in this case, an electrophysiological study offers relevant information. QRS complex aspect depends on the origin site of the tachycardia  .
The distinction between monomorphic VT and supraventricular tachycardia with aberrant conduction is made using Brugada  and Verekei  criteria, like atrioventricular dissociation, captures and fusion beats or a negative QRS complex in aVR during abnormal conduction of SVT. Signal-averaged ECG is also useful in differentiating between the two entities .
Blood workup in VT patients should include potassium, magnesium, calcium levels, toxicology screening, digoxin, troponin I or T levels. Echocardiography should be performed, as it may find the structural etiology of the arrhythmia like right ventricular or global cardiomyopathies or post-ischemic scars. Genetic testing for Brugada and long QT syndromes and catecholaminergic polymorphic VT is also useful.