The normal heart between the rate of 60 to 100 beats per minute in a regular fashion. In certain conditions, the heart can beat quite fast – fast enough to cause the patients symptoms and sometimes be life-threatening. One such condition where the heart beats very fast is ventricular tachycardia. Here we take a look at this condition in a little more detail.
The term ‘ventricular tachycardia’ seems to be a long and complex one. To simplify it, let us split the term into its constituents and see what each word actually means. The word ‘ventricular’ refers to ventricles, which is the bottom chamber of the heart (the heart has four chambers through which blood flows – two ventricles and two atria). The ventricles carry out the important function of pumping blood to all parts of the body. The term ‘tachycardia’ refers to a fast heartbeat.
Numerically this ranges from 100-120 beats per minute though it can rise up to over 250 beats per minute.
Now, you might think that even during an exercise the heartbeat tends to pump at about 120 – 150 beats per minute, so does that mean that you having ventricular tachycardia?
Fortunately, it does not.
In a VT, the increased contraction occurs in a fashion where 3 or more consecutive beats are irregular. This is not seen when exercising. Furthermore, in a VT, the electrical activity originates from the bottom chambers itself, rather than from the top chamber (which happens normally).
How does ventricular tachycardia occur?
To understand VT better it is important to understand the normal conducting system of the heart.
The electrical impulse arises from a specialised tissue located in the right atrium called the Sino-Atrial Node. The impulse then travels near the junction of the four chambers to reach another specialised tissue called the Atrio-Ventricular Node. After which the impulse travels through a collection of specialised heart muscles called the Bundle of His finally to end in the ventricles causing them to contract.
The ability of the heart muscle to generate electrical impulses without the need for any stimulus is called ‘automaticity’.
VT can occur in two scenarios – in a normal heart or in a diseased heart.
1. If VT occurs in a normal heart, it is due to an increase in automaticity, which means that electrical impulse is generated at a faster rate than expected.
2. If VT occurs in a diseased heart (from a previous myocardial infarction or structural problems), it is due to the scars present over the heart. Scars over the heart reduce the speed of electrical impulses and eventually leads to development of abnormal electrical circuits. These circuits are responsible for the VT, and are called ‘re-entry circuits’.
So what happens next? As the heart is beating so fast, it does not have sufficient time to fill up and pump blood to the vital organs and the rest of the body. This is what leads to symptoms.
What are the causes of a ventricular tachycardia?
There may be a number of reasons why a patient could develop a VT. Some of the common reasons are listed below.
1. Ischemic Heart Disease – This is the most common cause. Here there is narrowing of the heart arteries leading to insufficient blood reaching the heart muscle. This can stimulate VT which may be life threatening.
2. Congenital Heart Diseases – These are certain birth defects.
3. Structural heart diseases that disrupt normal electrical impulse conduction like cardiomyopathies.
4. Electrolyte imbalances: Conditions such as low calcium (hypo-calcemia), low magnesium (hypo-magnesemia) and low potassium (hypo-kalemia).
5. Toxicity due to overdose of the drug Digoxin (rare)
6. Inflammatory diseases like rheumatoid arthritis and sarcoidosis
7. Use of illicit drugs like cocaine and methamphetamine
8. Drugs like halothane (an anaesthetic agent) and anti-arrhythmics (drugs used in the treatment of heart rhythm problems)
9. Syndromes affecting ion channels. These are rare and include conditions such as Brugada syndrome.
What are the risk factors to develop VT?
Any patients having a previous history of coronary artery disease or heart attack are more prone to suffer from VT. However, those who take regular medication may be at a lower risk.
A point to be mentioned here is that patients with VT can have a strong family history. So one needs to find out if there were any unexplained premature deaths in the family (premature being age less than 40 years).
VT is very rare in young patients unless they are already suffering from a congenital heart disease (birth defect). It tends to affect the middle aged population. VT is more prevalent among men than women.
What are the symptoms of ventricular tachycardia?
Patients who suffer from a VT may experience –
Loss of consciousness
Diagnosis of ventricular tachycardia
Patients who are suffering from a VT often require the following investigations –
ECG – This will confirm the diagnosis. The findings on the ECG are quite unique.
Echocardiogram – This can help detect the presence of any abnormalities of the heart structure.
Coronary angiogram – This can detect coronary artery disease that may lead to VT.
Holter monitor – If patients are experiencing short bursts of VT, then a holter monitor can help determine the severity of the condition.
Electrophysiological studies – This study involves finding the location of the extra electrical generators so that they may be individually treated. It is often conducted in high risk patients.
These are some of the common tests. Rarely, additional tests will be performed.
Treatment of ventricular tachycardia
Patients must adopt a healthy lifestyle – one that is low in salt and low in fat. Stimulants such as caffeine (in coffee) and alcohol must be avoided. Smoking must be avoided.
The main aim of treatment here is to restore the normal electrical activity of the heart. This can be done in the following ways:
1. Drug therapy
Anti-arrhythmic drugs like Amiodarone, Procainamide and Lidocaine along with beta blockers like Metaprolol can be given. This helps in slowing down the heart rate as well as reducing the frequency of irregular beats.
This modality of this treatment implements the use of a bi-phasic shock at 100-150 J. In other words, a small shock is administered to the heart in order to ‘reset’ it to a normal rhythm.
3. Catheter Ablation
This method sends out radio-frequency waves which help in destroying areas that are producing extra impulses or areas where there is a re-entry circuit. This helps in abolishing the irregular waves and bring the heart back to its normal rhythm.
4. Implantable Cardioverter Defibrillator (ICD)
This specialised device keeps a check on any extra and irregular impulses. It detects these impulses and sends out an electrical discharge to counter them to negate their effect.
You can read more about ICD here.
5) Correction of Electrolyte Imbalance
Any abnormalities in the levels of salt can be corrected through tablets or through a drip.
Complications of ventricular tachycardia
If VT is not corrected as soon as possible, the patient can experience rather troublesome symptoms. Some cases can be life-threatening. All patients with documented VT require aggressive therapy and are often admitted to the coronary care unit.