What Is Tachycardia? What Causes Tachycardia?
Tachycardia refers to a faster than normal resting heart rate - the heart rate of a resting or sleeping individual is faster than it should be. In humans, the threshold of a normal heart rate (pulse) is generally based on the person's age. Tachycardia can be dangerous; depending on how hard the heart has to work.
In general, the adult resting heart beats between 60 and 100 times per minute (some doctors place the healthy limit at 90). When an individual has tachycardia the upper or lower chambers of the heart beat significantly faster - sometimes this happens to both chambers.
When the heart beats too rapidly, it pumps less efficiently and blood flow to the rest of the body, including the heart itself is reduced. The higher-than-normal heartbeat means there is an increase in demand for oxygen by the myocardium (heart muscle) - if this persists it can lead to myocardial infarction (heart attack), caused by the dying off of oxygen-starved myocardial cells.
Some patients with tachycardia may have no symptoms or complications. Tachycardia significantly increases the risk of stroke, sudden cardiac arrest or death.
Our heart rates are controlled by electrical signals which are sent across heart tissues. When the heart produces rapid electrical signals tachycardia occurs.
According to Medilexicon's medical dictionary:
- Tachycardia means "Rapid beating of the heart, conventionally applied to rates over 90 beats per minute."
What are the signs and symptoms of tachycardia?A symptom is something the patient feels and reports, while a sign is something other people, such as the doctor detect. For example, pain may be a symptom while a rash may be a sign.
When the heart beats too rapidly blood may not be pumped to the rest of the body effectively; this may affect organs and tissues which are deprived of oxygen. The following signs and symptoms of tachycardia are possible:
- Accelerated heart rate (fast pulse)
- Chest pain (angina) - chest pain or discomfort that occurs when the heart muscle does not get enough blood. Angina is more likely if the heartbeat is very fast and the heart is being put under a lot of strain.
- Hypotension (low blood pressure)
- Palpitations - an uncomfortable racing feeling in the chest, sensation of irregular and/or forceful beating of the heart.
- Panting (shortness of breath)
- Sudden weakness
- Syncope (fainting)
What are the risk factors for tachycardia?A risk factor is something which increases the likelihood of developing a condition or disease. For example, obesity significantly raises the risk of developing diabetes type 2. Therefore, obesity is a risk factor for diabetes type 2. As you will see below, there is some overlap between risk factors and causes.
Tachycardia risk is increased if the patient has a condition which either damages heart tissue and/or puts a strain on the heart. The following conditions are linked to a higher risk of tachycardia:
- Age - people over the age of 60 have a significantly higher risk of experiencing tachycardia, compared to younger individuals.
- Consuming large quantities of alcohol regularly
- Consuming large quantities of caffeine
- Genetics - people who have close relatives (e.g. parents) with tachycardia or other heart rhythm disorders have a higher risk of developing the condition themselves, compared to other individuals.
- Heart disease
- Hypertension (high blood pressure)
- Mental stress
- Using recreational drugs
What are the causes of tachycardia?Tachycardia is generally caused by a disruption in the normal electrical impulses that control our heart's pumping action rhythm - the rate at which our heart pumps. The following situations, conditions and illnesses are possible causes:
- A reaction to certain medications
- Congenital (present at birth) electrical pathway abnormalities in the heart
- Congenital abnormalities of the heart
- Consuming too much alcohol
- Consumption of cocaine and some other recreational drugs
- Electrolyte imbalance
- Heart disease which has resulted in poor blood supply and damage to heart tissues, including coronary artery disease (atherosclerosis), heart valve disease, heart failure, heart muscle disease (cardiomyopathy), tumors, or infections.
- Hyperthyroidism (overactive thyroid gland)
- Certain lung diseases
Atria, ventricles and the electrical circuitry of the heart
The human heart consists of four chambers:
- Atria - the two upper chambers; a left atrium and a right atrium.
Ventricles - the two lower chambers; a left ventricle and a right ventricle.
The electrical impulses leave the sinus mode and go across the atria, making the atria muscles contract. This atria muscle contraction pushes blood into the ventricles.
The electrical impulses continue to the atrioventricular node (AV node), a cluster of cells. The AV node slows down the electrical signals, and then sends them on to the ventricles. By delaying the electrical signals the AV node is able to give the ventricles time to fill with blood first. When the ventricle muscles receive the electrical signals they contract, pumping blood either to the lungs or the rest of the body.
When there is a problem with the electrical signals resulting in a faster-than-normal heartbeat, the patient has tachycardia. The most common types of tachycardia include:
- Atrial fibrillation - When the two upper chambers - the atria - contract at an excessively high rate, and in an irregular way, the patient has atrial fibrillation. During atrial fibrillation the contractions of the two upper chambers of the heart are not synchronized with the contractions of the two lower chambers, causing rapid and irregular heartbeats. Atrial fibrillation is caused by chaotic electrical impulses in the atria; the AV node is bombarded with chaotic signals. An atrial fibrillation episode may last from a few hours to several days. Sometimes the episode does not go away without treatment. Most atrial fibrillation patients have some heart abnormality related to the condition.
- Atrial flutter - the atria beats rapidly, but regularly. It is caused by a circuit problem within the atria. The contractions of the atria are weak because of the rapid heartbeat. There is a rapid and sometimes irregular ventricular rate, caused by rapid signals entering the AV node. An atrial flutter episode may last a few hours or some days. Sometimes it may not go away until treated. Atrial flutter is sometimes a complication of surgery, but it also can be caused by various forms of heart disease. Patients with atrial flutter commonly experience atrial fibrillation too.
- Supraventricular tachycardias (SVTs) - any tachycardic (accelerated) heart rhythm originating above the ventricular tissue. The abnormal circuitry in the heart if usually congenital (present at birth) and creates a loop of overlapping signals. An SVT episode may last from a few seconds to several hours. In one SVT form the AV node splits the electrical signal in two, with one signal going to the ventricles while the other goes back to the atria. There may also be an extra electrical pathway from the atria to the ventricles, effectively bypassing the AV node and resulting in a signal going down one pathway and up the other.
- Ventricular tachycardia - abnormal electrical signals in the ventricles result in a rapid heart rate. The speed of the heart beat does not allow the ventricles to fill and contract properly, resulting in poor blood supply to the body. This type of tachycardia is frequently a life threatening condition and is treated as a medical emergency. Ventricular tachycardia is linked to heart muscle damage from a previous heart attack or cardiomyopathy (disease of the heart muscle).
- Ventricular fibrillation - the ventricles quiver in an ineffective way, resulting in poor blood supply to the body. If normal heart rhythm is not restored rapidly, blood circulation will cease and the patient will die. Patients with an underlying heart condition, or those who have been struck by lightning causing serious trauma may experience ventricular fibrillation.
How is tachycardia diagnosed?A good doctor can usually diagnose has tachycardia and what type it is by asking the patient some questions regarding symptoms, carrying out a physical exam, and ordering some tests. These may include:
- Blood tests - these help determine whether thyroid problems or other substances may be factors contributing to the patient's tachycardia. Blood tests can also reveal whether the individual has anemia, or problems with kidney function, which could complicate some tachycardias. Serum electrolytes may also be tested to determine sodium and potassium levels.
- Electrocardiogram (ECG) - electrodes are attached to the patient's skin to measure electrical impulses given off by the heart. The impulses are recorded as waves and displayed on a screen (or printed). This test will also show any previous heart disease that may have contributed to the tachycardia. The abnormality of the heart action is generally obvious right away. The doctor will look for patterns to determine what type of tachycardia the patient has.
- Holter monitor - the patient wears a portable device which records all their heartbeats. It is worn under the clothing and records information about the electrical activity of the heart while the person goes about his/her normal activities for one or two days. It has a button which can be pressed if symptoms are felt - then the doctor can see what heart rhythms were present at that moment.
- Event recorder - This device is similar to a Holter monitor, but it does not record all the heartbeats. There are two types:
- One uses a phone to transmit signals from the recorder while the patient is experiencing symptoms.
- The other is worn all the time for a long time; sometimes as long as a month (it must be taken off when showering or having a bath).
- Electrophysiological testing (EP studies)- This is an invasive, relatively painless, non-surgical test and can help determine the type of arrhythmia, its origin, and potential response to treatment.
The test is carried out in an EP lab by an electrophysiologist, and makes it possible to reproduce troubling arrhythmias in a controlled setting. During an EP study:
- The patient is given a local anesthetic.
- After an initial puncture an introducer sheath is inserted into a blood vessel.
- A catheter is inserted through the introducer sheath and is threaded up the blood vessel, through the body and into the right chambers of the heart.
- The electrophysiologist can see the catheter moving up the body on a monitor.
- When it is inside the heart the catheter stimulates the heart and records where abnormal impulses start, their speed, and which normal conduction pathways they bypass.
- Treatments can be given to find out whether they stop the arrhythmia.
- The catheter and introducer sheaths are then removed, and the insertion site is closed up either by applying pressure to the site or with stitches.
- Tilt-table test - if the patient experiences fainting spells, dizziness or lightheadedness, and neither the ECG nor the Holter revealed any arrhythmias, a tilt-table test may be performed. This monitors the patient's blood pressure, heart rhythm and heart rate while he/she is moved from a lying down to an upright position.
A healthy patient's reflexes cause the heart rate and blood pressure to change when moved to an upright position - this is to make sure the brain gets an adequate supply of blood.
If the reflexes are inadequate they could explain the fainting spells, etc.
- Chest X-ray - the X-ray images help the doctor check the state of the individual's heart and lungs. A chest X-ray may also help a doctor determine whether any congenital heart defects are present. Other conditions that may explain the signs and symptoms might also be detected.
What are the treatment options for tachycardia?Treatment options vary, depending on what caused the condition, the patient's age and general health, and some other factors. The aim is to slow down an accelerated heartbeat when it occurs, prevent subsequent episodes of tachycardia and reduce risk complications. In some cases all that is required is to treat the cause, as may be the case with hyperthyroidism (an overactive thyroid gland). In some cases no underlying cause is found and the doctor may have to try out different therapies.
Ways to slow down a fast heartbeat:
- Vagal maneuvers - this is a maneuver which affects the vagal nerve. The vagal nerve helps regulate our heartbeat. Maneuvers may include coughing, heaving (as if you were having a bowel movement), and placing an icepack on the patient's face. If this does not stop the rapid heartbeat the patient may need an anti-arrhythmic medication.
- Medication - an anti-arrhythmic injection is administered to restore a normal heartbeat. This is done in a hospital. The doctor might prescribe an oral anti-arrhythmic drug, such as flecainide (Tambocor) or propafenone (Rythmol).
Controlling tachycardia can be approached in two ways:
- The normal heart rhythm can be restored.
- The rate at which the heart beats can be controlled.
- Restore normal heart rhythm.
- Control the heart rate.
- Both restore normal heart rhythm and control the heart rate.
- The type of tachycardia.
- Other medical conditions the patient might have.
- Side effects of the chosen drug.
- How well the patient's condition responds to treatment.
- Cardioversion - paddles or patches are used to deliver an electric shock to the heart. This affects the electrical impulses in the heart and restores normal rhythm. This is carried out in a hospital. Doctors say that cardioversion has a success rate of over 90% in early-diagnosed patients. Cardioversion may be used when emergency care is needed, or when other therapies have not worked.
- Radiofrequency catheter ablation - this treatment is generally used when the tachycardia is caused by an extra electrical pathway. Catheters enter the heart via blood vessels. Electrodes at the ends of the catheter are heated to ablate (damage) the extra pathway, stopping it from sending electrical signals. Radiofrequency catheter ablation is especially effective for patients with supraventricular tachycardia. This procedure may also be used for atrial fibrillation and atrial flutter.
- Medications - when taken regularly anti-arrhythmic medications may prevent tachycardia. Patients may be prescribed other medications which may be taken in combination with anti-arrhythmics, for example, channel blockers, such as diltiazem (Cardizem) and verapamil (Calan), or beta blockers, such as propranolol (Inderal) and esmolol (Brevibloc).
- ICD (implantable cardioverter defibrillator) - the device, which continuously monitors the patient's hearbeat, is surgically implanted into the chest. The ICD detects any heartbeat abnormality and delivers electric shocks to restore normal heart rhythm.
- Surgery - sometimes surgery is needed to destroy an extra electrical pathway. The surgeon may create a pattern or maze of scar tissue. Scar tissue is a bad conductor of electricity. This procedure is generally only used when other therapies have not been effective, or if the patient has another heart disorder.
It is crucial that the patient takes the Warfarin as directed by the doctor. As Warfarin can interact harmfully with many medications, it is vital that the patient and doctor check for this every time a new medication is prescribed or bought over the counter. A trained pharmacist will know which medications interact with Warfarin. Even alcohol and cranberry juice can affect Warfarin.
What are the possible complications of tachycardia?The risk of complications depends on several factors, including:
- The severity
- The type
- The rate of tachycardia
- The duration of tachycardia
- Whether or not other heart conditions are present
- Blood clots - these significantly increase the risk of heart attack or stroke.
- Heart failure - if the condition is not controlled the heart is likely to get weaker. This may lead to heart failure. Heart failure is when the heart does not pump blood around the body efficiently or properly. The patient's left side, right side, or even both sides of the body can be affected.
- Fainting spells
- Sudden death - generally only linked to ventricular tachycardia or ventricular fibrillation