Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is a disorder in the heart rhythm pattern, which involves abnormally high heart rate, lasting few seconds in some cases to days together in other cases. These episodes of irregular heart beat can occur regularly or infrequently.
The heart rate may rise up to 300 pulses a minute, but usually stays between 140 and 180. It is caused by fast, abnormal, electrical impulses that originate in the atria and supersede the pacemaker function. Attacks come up without any apparent reason but can be triggered due to physical exertion, emotional stress, and caffeine or alcohol intake.
In majority of cases, heart function is normal; it is just the symptoms which cause discomfort.

Symptoms

The most common symptom associated with SVT is palpitations or a feeling of heart throbbing in the chest. Other symptoms include

• Pain in chest
• Giddiness and light-headedness
• Shortness of breath
• Exhaustion
• In rare cases, decline in blood pressure can cause fainting.

Causes

The normal heart rate is harmonized by an assortment of muscle fibres in the right side upper chamber of heart. This is called sinoatrial node and it behaves like heart’s natural pacemaker.
In SVT, high-speed impulses begin at a point above the ventricles and supersede the natural pacemaker. SVT has numerous different types of arrhythmias. The commonest type is paroxysmal supraventricular tachycardia (PSVT) which is in fact temporary bouts of abnormal heart rhythm. PSVT occurs due to a short circuit in the electrical mechanism of the heart which causes electrical stimuli to go round in circles, making the heart work at a faster pace.
Another type of SVT is Wolff-Parkinson-White syndrome in which there is an abnormal electrical link between the atria and ventricles of the heart. The added tissue leads to a short circuit between the two chambers, causing the heart to beat faster.
In SVT, the heart rate is high enough to tire the heart muscles as they do not get relaxation time between contractions. This decreases the blood supply to the rest of the body.
Another cause for SVT may be side effects of medicines like digitalis, herbal supplements, asthma drugs and cold treatments.
High caffeine intake and high stress levels can also increase risk of arrhythmias.
There are still some cases of SVT in which causes are unclear.

Diagnosis

A confirmed diagnosis can be obtained through an ECG or electrocardiogram during a period of SVT. An ECG is done to trace heart’s rhythm and electrical system. They also monitor and record the abnormal activity in the heart’s electrical signals. During the test, electrodes are positioned on the patient’s chest, arms and legs and findings are recorded on a printed graph paper. In some cases, ECG might be done for 24 hours to monitor alteration in heart’s rhythm over the day.
One may need further examination after confirmation of SVT diagnosis, to determine the specific site in the heart which is responsible for producing SVT episodes.

Treatment

In several cases, symptoms of the condition get resolved fast, without any treatment.
In order to stop SVT episodes through different treatment options, one needs to have results from an ECG done in the hospital.
Non-drug methods of treatment – Valsalva manoeuvre is a non-drug treatment technique which involves holding the nose, closing the mouth and breathing out strongly. Another non-drug method is to have somebody massage the carotid sinus in the neck.
Medications – in severe cases, with symptoms lasting too long, intravenous medications can help in blocking the electrical stimuli in the heart. These include intravenous adenosine or verapamil as a substitute for people with asthma. Medicines like digoxin, verapamil and beta blockers can be prescribed to avert further SVT episodes.
Electric shock treatment – the cardio version of this treatment is given under anaesthesia to halt an SVT episode. This is not a common treatment.
Radio frequency ablation – in this procedure, catheters are positioned inside the patient’s heart and a chart of its electrical system is drawn. This helps get to the root cause of abnormality for which high-energy radio waves are given to get rid of the tissue. Ablation has proved to be highly successful in treating SVT.