Ventricular tachycardia
Ventricular tachycardia | |
---|---|
Other names | V-tach, calcium channel blockers, amiodarone[2] |
Treatment | Procainamide, cardioversion, cardiopulmonary resuscitation[2][5] |
Frequency | ~7% of people in cardiac arrest[2] |
Ventricular tachycardia (V-tach or VT) is a
Ventricular tachycardia can occur due to
In those who have normal
Signs and symptoms
While a few seconds may not result in problems, longer periods are dangerous.[3] Short periods may occur without symptoms or present with lightheadedness, palpitations, shortness of breath, chest pain, or unconsciousness.[2] Ventricular tachycardia may turn into ventricular fibrillation and can result in cardiac arrest.[2][3]
Cause
Ventricular tachycardia can occur due to
Pathophysiology
The morphology of the tachycardia depends on its cause and the origin of the re-entry electrical circuit in the heart.[citation needed]
In monomorphic ventricular tachycardia, the shape of each heart beat on the ECG looks the same because the impulse is either being generated from increased
Polymorphic ventricular tachycardia, on the other hand, is most commonly caused by abnormalities of ventricular muscle repolarization. The predisposition to this problem usually manifests on the ECG as a prolongation of the QT interval. QT prolongation may be congenital or acquired. Congenital problems include long QT syndrome and catecholaminergic polymorphic ventricular tachycardia. Acquired problems are usually related to drug toxicity or electrolyte abnormalities, but can occur as a result of myocardial ischemia. Class III anti-arrhythmic drugs such as sotalol and amiodarone prolong the QT interval and may in some circumstances be pro-arrhythmic. Other relatively common drugs including some antibiotics and antihistamines may also be a danger, in particular in combination with one another. Problems with blood levels of potassium, magnesium and calcium may also contribute. High-dose magnesium is often used as an antidote in cardiac arrest protocols.[citation needed]
Diagnosis
The
Various diagnostic criteria have been developed to determine whether a wide complex tachycardia is ventricular tachycardia or a more benign rhythm.
The proper diagnosis is important, as the misdiagnosis of supraventricular tachycardia when ventricular tachycardia is present is associated with worse prognosis. This is particularly true if calcium channel blockers, such as verapamil, are used to attempt to terminate a presumed supraventricular tachycardia.[11] Therefore, it is wisest to assume that all wide complex tachycardia is VT until proven otherwise.[citation needed]
ECG features of Ventricular Tachycardia in addition to the increased Heart rate are:
- A wide QRS Complex (because the ectopics for the generation of the cardiac impulse originates in the Ventricular Myocyte and propagated via the intermyocyte conduction, which is a delayed conduction)
- A Josephson's sign where there is the notch in the downsloping of the S wave near its nadir (considered very specific for the VT).
- Capture beats (normal QRS complex in between when the Heart pick up the sinus rhythm from the impulses generated by the SA node), fusion beats (due to the fusion of the Abnormal and the Normal QRS complexes) which has a unique morphology.
- Positive or negative concordance.
- Extreme Axis deviationor NORTH WEST axis (axis between -90 and +180 degrees)
Classification
Ventricular tachycardia can be classified based on its morphology:[citation needed]
- Monomorphic ventricular tachycardia means that the appearance of all the beats match each other in each lead of a surface electrocardiogram(ECG).
- Scar-related monomorphic ventricular tachycardia is the most common type and a frequent cause of death in patients having survived a heart attack, especially if they have weak heart muscle.[12]
- right ventricular outflow tract. RVOT morphology refers to the characteristic pattern of this type of tachycardia on an ECG.[citation needed]
- The source of the re-entry circuit can be identified by evaluating the morphology of the QRS complex in the V1 lead of a surface ECG. If the R wave is dominant (consistent with a right bundle branch block morphology), this indicates the origin of the VT is the left ventricle. Conversely, if the S wave is dominant (consistent with a left bundle branch block morphology, this is consistent with VT originating from the right ventricle or interventricular septum.[12]
- Polymorphic ventricular tachycardia, on the other hand, has beat-to-beat variations in morphology. This may appear as a cyclical progressive change in cardiac axis, previously referred to by its French name torsades de pointes ("twisting of the spikes"). However, at the current time, the term torsades de pointes is reserved for polymorphic VT occurring in the context of a prolonged resting QT interval.[citation needed]
Another way to classify ventricular tachycardias is the duration of the episodes: Three or more beats in a row on an ECG that originate from the ventricle at a rate of more than 120 beats per minute constitute a ventricular tachycardia.[citation needed]
- If the fast rhythm self-terminates within 30 seconds, it is considered a non-sustained ventricular tachycardia.
- If the rhythm lasts more than 30 seconds, it is known as a sustained ventricular tachycardia (even if it terminates on its own after 30 seconds).
A third way to classify ventricular tachycardia is on the basis of its symptoms: Pulseless VT is associated with no effective cardiac output, hence, no effective pulse, and is a cause of cardiac arrest (see also:
Occasionally in ventricular tachycardia, supraventricular impulses are conducted to the ventricles, generating QRS complexes with normal or aberrant supraventricular morphology (ventricular capture). Or, those impulses can be merged with complexes that are originated in the ventricle and produce a summation pattern (fusion complexes).[13]
Less common is ventricular tachycardia that occurs in individuals with structurally normal hearts. This is known as idiopathic ventricular tachycardia and in the monomorphic form coincides with little or no increased risk of sudden cardiac death. In general, idiopathic ventricular tachycardia occurs in younger individuals diagnosed with VT. While the causes of idiopathic VT are not known, in general it is presumed to be congenital, and can be brought on by any number of diverse factors.[citation needed]
Treatment
Therapy may be directed either at terminating an episode of the abnormal heart rhythm or at reducing the risk of another VT episode. The treatment for stable VT is tailored to the specific person, with regard to how well the individual tolerates episodes of ventricular tachycardia, how frequently episodes occur, their comorbidities, and their wishes. Individuals with pulseless VT or unstable VT are hemodynamically compromised and require immediate electric cardioversion to shock them out of the VT rhythm.[14]
Cardioversion
If a person still has a pulse, it is usually possible to terminate the episode using electric cardioversion.[15] This should be synchronized to the heartbeat if the waveform is monomorphic if possible, in order to avoid degeneration of the rhythm to ventricular fibrillation.[15] An initial energy of 100J is recommended.[15] If the waveform is polymorphic, then higher energies and an unsynchronized shock should be provided (also known as defibrillation).[15]
Defibrillation
A person with pulseless VT is treated the same as ventricular fibrillation with high-energy (360J with a monophasic defibrillator, or 200J with a biphasic defibrillator) unsynchronised cardioversion (defibrillation).[15] They will be unconscious.
The shock may be delivered to the outside of the chest using the two pads of an external defibrillator, or internally to the heart by an implantable cardioverter-defibrillator (ICD) if one has previously been inserted.[citation needed]
An ICD may also be set to attempt to overdrive pace the ventricle. Pacing the ventricle at a rate faster than the underlying tachycardia can sometimes be effective in terminating the rhythm. If this fails after a short trial, the ICD will usually stop pacing, charge up and deliver a defibrillation grade shock.[citation needed]
Medication
For those who are stable with a
As a
Long-term anti-arrhythmic therapy may be indicated to prevent recurrence of VT. Beta-blockers and a number of class III anti-arrhythmics are commonly used, such as the beta-blockers carvedilol, metoprolol, and bisoprolol, and the Potassium-Channel-Blockers amiodarone, dronedarone, bretylium, sotalol, ibutilide, and dofetilide. Angiotensin-converting-enzyme (ACE) inhibitors and aldosterone antagonists are also sometimes used in this setting.[17]
Invasive treatment
An ICD (implantable cardioverter defibrillator ) is more effective than drug therapy for prevention of sudden cardiac death due to VT and VF, but does not prevent these rhythm from happening.
In the past, ablation was often not considered until pharmacological options had been exhausted, often after the patient had developed substantial morbidity from recurrent episodes of VT and ICD shocks. Antiarrhythmic medications can reduce the frequency of ICD therapies, but have efficacy varies and side effects can be significant. Advances in technology and understanding of VT substrates now allow ablation of multiple and unstable VTs with acceptable safety and efficacy, even in patients with advanced heart disease.[20]
References
- ^ "Ventricular tachycardia: MedlinePlus Medical Encyclopedia". medlineplus.gov. Retrieved 29 May 2019.
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- ^ a b c d e f g h i "Types of Arrhythmia". NHLBI. July 1, 2011. Archived from the original on 7 June 2015. Retrieved 7 September 2016.
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- ^ PMID 26472989.
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