Monomorphic Ventricular Tachycardia - An Overview

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What is Monomorphic Ventricular Tachycardia

Ventricular tachycardia (VT) is a rapid heart beat which arises in the lower chambers (ventricles) of the heart. In VT, the heartbeat is more than 100-120 beats per minute. It is a potentially life threatening condition as it can lead to stoppage of heart and sudden death. In monomorphic ventricular tachycardia, all the beats look the same in each lead of an electrocardiogram.

Pathophysiology

In monomorphic ventricular tachycardia, all the beats match each other in appearance because they arise from increased automaticity of a single point either in the left or right ventricle.

The most common causes of this condition are:

1. Scarring of the heart muscle from a previous heart attack - This scar cannot conduct electrical activity so there is a potential circuit around the scar which generates the electrical activity.

2. Primary cardiomyopathy

3. Surgical scar

4. Muscle degeneration

Monomorphic VTs can occur rarely in the absence of any heart disease. These are usually classified according to their site of origin. These are:

1. Right ventricle outflow tract

2. Left ventricle outflow tract

3. Left ventricle septum

4. Root of aorta

In monomorphic VT, the risk of mortality correlates with the degree of structural heart disease. The more severe the heart disease, the more is the risk of mortality.

Symptoms

The main symptoms of Monomorphic VT are:

1. Palpitations

2. Lightheadedness

3. Unconsciousness

4. Chest pain

5. Breathlessness

6. Hypotension

7. Anxiety

Laboratory Workup

The laboratory workup to be done in case of ventricular tachycardia is:

1. Electrocardiography (ECG) - This is the most important investigation for diagnosis.

2. Serum electrolytes

3. Echocardiography

4. Coronary angiography

5. Chest radiograph - This is done to evaluate pulmonary congestion.

6. Cardiac CT scan and MRI

Management

Acute monomorphic VT is a medical emergency and the immediate step is to achieve conversion of tachycardia to normal rhythm.

The different modalities of treatment used are:

1. Intravenous drugs like lidocaine, amiodarone and procainamide are used.

2. If these drugs fail, then synchronized cardioversion shock following sedation is appropriate.

3. Implantable cardioverter defibrillator (ICD) - This device can be implanted in the heart in a brief low risk procedure. It can detect ventricular tachycardias and terminate them.

Preventive Measures

The long term management of ventricular tachycardia is prevention of further attacks. The various measures undertaken for this purpose are as follows:

1. Diet - Low cholesterol and low salt diets are beneficial. Stimulants like caffeine should be avoided.

2. Patient can resume normal active lifestyle under cover of medications.

3. Amiodarone and sotalol are the two medications commonly used for long term suppression of ventricular tachycardia. The other drugs used are metoprolol, propafenone, mexiletine and quinidine.

Long term close follow up of patients with monomorphic ventricular tachycardia forms an integral part of long term management of these patients.

References

  1. Manual of Cardiovascular Medicine by Brian P. Griffin
  2. Comprehensive Coronary Care by Nigel I. Jowett, David R. Thompson, Roger Boyle
  3. Cardiac arrhythmia: mechanisms, diagnosis, and management by Philip J. Podrid, Peter R. Kowey