What is Supraventricular Tachycardia?
Supraventricular tachycardia (SVT) is an irregular heartbeat that starts at or above a part of your heart called the atrioventricular (AV) node. It’s identified by a fast, narrow heartbeat (less than 120 milliseconds) that exceeds 100 beats per minute.
A condition known as atrioventricular nodal reentrant tachycardia (AVNRT), sometimes referred to as paroxysmal SVT, is an intermittent bout of SVT that does not have any trigger factors. It usually leads to a specific heart pattern of 160 beats per minute.
What Causes Supraventricular Tachycardia?
When doctors try to figure out what might be causing your symptoms, they consider all the possible conditions that could be at fault. This is called a ‘differential diagnosis’. In the case of supraventricular tachycardia (SVT), where your heart beats faster than normal, other possible conditions could be sinus tachycardia, atrial tachycardia, junctional tachycardia, atrial fibrillation, atrial flutter or multi atrial tachycardia. These names all refer to different types of abnormal heart rhythms.
If you are likely to have SVT, there are several things that could set it off or ‘trigger’ it. These include certain medications, caffeine, alcohol, physical or emotional stress, and smoking cigarettes.
Risk Factors and Frequency for Supraventricular Tachycardia
Atrioventricular nodal reentrant tachycardia, a type of abnormal heart rhythm, happens in about 35 out of every 10,000 people per year or 2.29 per 1000 people. It’s the most common non-normal heart rhythm in young adults. Women are twice as likely to get it as men are, and older people are five times more likely than younger ones.
This sort of abnormal heart rhythm is the most common symptomatic one in infants and children. Children with congenital heart disease, which is when the heart or blood vessels near the heart don’t develop normally before birth, have a higher risk. Also, in children under the age of 12, it’s usually caused by an extra pathway in the heart that causes faster heartbeats.
showing the Sinoatrial node, Atrioventricular node, Bundle of His, Purkinje
fibers, and Bachmann’s bundle
Signs and Symptoms of Supraventricular Tachycardia
People with this condition often have feelings of anxiousness, heart palpitations, discomfort in the chest, dizziness, fainting, and difficulty breathing. In certain cases, individuals might have low blood pressure, signs of heart failure, lightheadedness, or trouble tolerating physical activity. Some people might not have any symptoms at all. In these cases, a rapid heart rate is often discovered during regular health screenings, like those at drugstores or with fitness trackers. The symptoms usually come on suddenly and can be brought on by physical or emotional stress.
During a physical exam, the only usual sign besides a rapid heart rate is a normal patient who has a good heart health reserve. For people who are starting to decompensate, there might be signs of congestive heart failure, such as bibasilar crackles (a crackling sound in the base of the lungs), a third heart sound (S3), or jugular venous distention (swelling of the jugular vein).
- Feelings of anxiousness
- Heart palpitations
- Discomfort in the chest
- Dizziness
- Fainting
- Difficulty breathing.
- Low blood pressure or signs of heart failure (in some cases)
- Trouble tolerating physical activity
- Condition could be discovered during regular health screenings with no prior symptoms
Testing for Supraventricular Tachycardia
The initial check for Supraventricular Tachycardia (SVT), a condition where your heart suddenly beats much faster than usual, is done by getting an Electrocardiogram (ECG), a test that monitors your heart’s electrical activity. Distinct features on this ECG might show a consistently high heart rate between 180 and 220 beats per minute, without visible P waves, which are usually seen in a normal heart rhythm. If they spot P waves, your doctor might think about other possible conditions like Sinus Tachycardia, Atrial Fibrillation, or Atrial Flutter.
After the initial ECG, they’ll continue testing to find out what might be causing your SVT. They might test you for things like imbalances in your body’s salts and minerals (electrolyte abnormalities), not enough red blood cells (anemia), or an overactive thyroid gland (hyperthyroidism). If you’re taking the medication Digoxin, your doctor might check your levels since too much can cause SVT.
Treatment Options for Supraventricular Tachycardia
When someone is identified as having what’s called a Supraventricular Tachycardia (SVT), or a fast heart rate originating from above the heart’s lower chambers, doctors look for signs of instability. These signs could include low blood pressure, low oxygen levels, shortness of breath, chest pain, shock, evidence of reduced blood flow to organs (poor end-organ perfusion), or changes in mental status.
If the patient is not stable, doctors may opt for immediate synchronized cardioversion. This means using a machine, called a defibrillator, to send electrical shocks to the heart to restore a normal heart rhythm. It’s crucial that the shocks are timed or “synced” with a specific part of the heart rhythm to prevent the shock from interfering while the heart is repolarizing (resetting for the next heartbeat). This is to prevent a type of chaotic heart rhythm, called polymorphic ventricular tachycardia, which can occur if the shock is incorrectly timed.
If the patient is stable, the medical team might try what is known as vagal maneuvers while preparing to chemically control the heart rate. Vagal maneuvers – such as the Valsalva maneuver and carotid massage – are simple actions that stimulate the body’s natural control system (the parasympathetic system) to slow the heart rate.
The Valsalva maneuver involves breathing out forcefully against a closed airway, similar to bearing down like you’re going to have a bowel movement. This is held for about 10 to 15 seconds. Carotid massage involves applying pressure to one side of the neck for about 10 seconds, and is not recommended for individuals with certain types of previous neurological symptoms or known neck (carotid artery) disease.
If these maneuvers aren’t enough, doctors may administer a medication called adenosine. This medicine must be administered rapidly through a large intravenous line for it to be effective. If adenosine doesn’t work, other medications may be used, such as diltiazem, esmolol, or metoprolol.
If the drugs aren’t enough, doctors might consider overdrive pacing, a method that aims to control the heart rhythm by pacing it at a rate faster than its own. However, this is used with caution as it can increase the risk of uncoordinated heart rhythms. This is why they’ll always have the equipment handy to convert the heart back to normal rhythm (cardioversion).
Indiviudals with recurring SVT without another syndrome called pre-excitation may need long-term treatment with oral medications known as beta-blockers or calcium channel blockers to maintain a normal heart rhythm. There’s also a procedure called radio-frequency ablation, which can be performed if an extra pathway in the heart’s electrical system can be found. This procedure can help prevent further episodes of SVT. People with recurring SVT can also learn how to perform vagal maneuvers themselves to manage their condition.
What else can Supraventricular Tachycardia be?
Here are some heart conditions that need to be considered:
- Atrial flutter
- Atrial tachycardia
- Atrial fibrillation
- Ventricular tachycardia
Possible Complications When Diagnosed with Supraventricular Tachycardia
The complications from treatment can be tied to either the medication or the procedure of radiofrequency ablation. This procedure is invasive and may lead to the following complications:
- A large bruise, also known as a Hematoma
- An abnormal blood-filled bulge of an artery wall, termed as Pseudoaneurysm of the artery
- Bleeding
- A heart attack, also referred to as Myocardial infarction
- Heart block and possible need for a pacemaker
- Stroke
- Death
