The heart has a simple electrical system that consists of an electrical generator and a series of cables that transmits electricity through the heart. The electrical signals that are generated by the sinoatrial node is responsible for the contraction of the heart.
We have detailed how electricity is conducted through the heart in this post here. Rhythmic electrical activity is responsible for effective contraction and relaxation of the heart muscle.
sometimes however, the heart can be rather fast and can cause palpitations. Patients can experience a rapid beating of the heart in their chest. While there can be number of causes for this, paroxysmal supraventricular tachycardia is one recognised cause. Here we take a closer look at this condition.
What is paroxysmal supraventricular tachycardia?
Paroxysmal supraventricular tachycardia, sometimes called PSVT, is a condition where there is abnormal conduction of electrical impulses through the heart. This causes both the atrium and ventricles to contract at a rapid rate.
The duration for which the heart contracts at this rapid rate is often short lived. For this reason, this condition is called paroxysmal (paroxysmal = short lived). Patients may experience short bursts of a fast heart rate when they are at home or at work which often resolves fairly quickly by itself. Sometimes however, the condition can last for a few hours.
Why does PSVT occur?
If we look at the electrical conduction system in the heart, there exists an electrical generator called the sinoatrial node. From there, the electricity is passed through a series of cables to the middle of the heart (called the atrioventricular node). From the middle of the heart, the electricity is further conducted through two bundles that supply the left and the right side of the heart muscle.
In paroxysmal supraventricular tachycardia, there is a problem with the atrioventricular node. Instead of the electricity passing in one direction through the atrioventricular node down to the ventricles, there exists another part of it i.e. another series of cables that they connects the atrioventricular node back to the sinus atrial node.
This means that when electricity travels from the sinoatrial node to the atrioventricular node, a part of it moves down to the ventricle while a part of it most backup to the atrium. This phenomenon where the electricity is conducted back to the top portion of the heart is called ‘re-entry’.
Re-entry phenomenon is what is responsible for an increase in the heart rate. Treatments that are offered to the patient are targeted towards this extra cable.
What are the causes of PSVT?
Some of the common factors that trigger a PSVT include –
- High alcohol and caffeine intake
- Abnormal levels of electrolytes in the blood
- Thyroid problems
- Certain medications used for colds and coughs
Sometimes, there may be no cause identified.
What are the symptoms of PSVT?
The symptoms that the patient experiences with paroxysmal supraventricular tachycardia can be variable. Some patients may only experience mild symptoms while those who have underlying heart disease may experience more severe symptoms. The common symptoms that are associated include –
1. Palpitations i.e. an experience that the heart is beating fast
2. Dizziness
3. Breathlessness
4. Collapsing episodes
5. Chest pain
6. Tiredness
7. Sweating, nausea and vomiting
These symptoms occur in varying frequencies but the top three are the most common symptoms. When patients experience PSVT, they can become rather anxious which can further increase the heart rate.
On examination of the patient, the heart rate will be between 150 and 180 beats per minute. The blood pressure may even be normal or low. Patients who have high blood pressure may have a higher recording of BP.
Patients who are breathless may have a small amount of fluid on the lungs which can be audible on clinical examination.
How is PSVT diagnosed?
Paroxysmal supraventricular tachycardia is best diagnosed by performing an electrocardiogram. Most patients who experience symptoms at home may find that the symptoms completely resolve by the time they reached their doctor’s clinic.
In patients in whom the ECG has not captured the abnormal rhythm and in those who have been experiencing regular symptoms, additional tests may be required. These include –
1. Holter recording – This test helps to record the heart rate over a period of 24 to 48 hours.
2. Echocardiogram – This helps identify any abnormalities in the structure of the heart muscle or the valves.
These are the common tests that are performed. However, some patients may need to undergo more specialised tests. These tests are called electrophysiological tests. The purpose of these tests is to find out where this extra cable that is transmitting electricity is present so that treatments can be given to the patient to stop conduction through this.
Treatment of paroxysmal supraventricular tachycardia
If the patient arrives to the doctor’s clinic with PSVT, an initial assessment of the patient is made. A clinical history will be obtained and the patient will be examined. The heart rate and blood pressure will be recorded. An ECG will be conducted to confirm the diagnosis.
Once a diagnosis of PSVT has been made, the doctor may try certain special manoeuvres that can sometimes flip the heart back into a normal rhythm. These include –
1. Valsalva manoeuvre – You may be aware of what this is. If you have a cold, cough and find that your ears are blocked, you may close both your nose and mouth and blow out forcefully in an attempt to open the ear canal. This manoeuvre is called Valsalva manoeuvre. A Valsalva manoeuvre may be performed by asking the patient to blow through the tip of a syringe or into a Mercury sphygmomanometers in an attempt to raise the level of Mercury.
2. Carotid sinus massage – There exists a small bundle of nerve fibers on the carotid artery in the neck. When stimulated, these can slow down the heartbeat. In patients with supraventricular tachycardia, massaging this sinus can sometimes stop the fast heart beating and change it back to normal heartbeat. Please note that this should not be attempted by patients and must be done by trained healthcare professionals only.
In some patients, the above methods may not be effective. In such patients, medical treatment with drugs may need to be commenced.
Medical therapy
1. Adenosine
This is a medicine that is injected into the veins. It is usually given to patients in hospital and not in a doctor’s clinic. This is because it can slow down the heart rate rather dramatically, and this is best done at a place where the heart rate can be monitored.
A small cannula is inserted into the patient’s vein (in the arm or the hand). The patient is attached to an ECG machine or a cardiac monitor. Adenosine is then injected through the vein at a rapid rate, following by a small injection of salt water. The drug acts on the AV node of the heart, and slows down the heart rate.
Most patients with PSVT respond well to adenosine. However, in those that do not, additional treatment options will need to be pursued.
Note: Adenosine is not administered in patients who have asthma or breathing problems. This is because it can cause a little difficulty breathing when it is injected.
2. Other medicines
If adenosine fails, other medication such as beta blockers, digoxin, calcium channel blockers and amiodarone may be administered.
Shock therapy
If PSVT does not change back to a normal rhythm with the above treatments, then patients may require special treatments. This kind of therapy is called cardioversion, sometimes called shock treatment.
Shock treatment is also reserved for patients who have PSVT with a low blood pressure and other associated symptoms.
Electrophysiological methods
In those in whom none of the methods work, special studies called electrophysiological studies (EPS) may be conducted.
EPS is a method of finding out where the extra pathway that is conducting electricity is present. Once these are found, they are destroyed using high frequency radio waves.
Preventing PSVT
It is not always possible to prevent PSVT from occurring.
Avoiding high amounts of alcohol and caffeine can help. If you are taking treatment for thyroid problems, make sure you get your thyroid function checked as recommended by your doctor.
In patients with recurring PSVT, EPS may be needed. This can be very effective.