Tachycardia refers to a fast resting heart rate - usually at least 100 beats per minute. Tachycardia can be dangerous, depending on its underlying cause and on how hard the heart has to work.
In general, the adult resting heart beats between 60 and 100 times per minute. When an individual has tachycardia, the upper and/or lower chambers of the heart beat significantly faster.
Our heart rates are controlled by electrical signals that are sent across the tissues of the heart. When the heart produces rapid electrical signals, tachycardia occurs.
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.
Because the heart is beating quicker, the muscles of the heart (myocardium) need more oxygen - if this persists, oxygen-starved myocardial cells can die off, leading to a heart attack (myocardial infarction).
Some patients with tachycardia may have no symptoms or complications. However, tachycardia significantly increases the risk of stroke, sudden cardiac arrest, and death.
Symptoms of tachycardia
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
- 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)
It is not unusual for some patients with tachycardia to experience no symptoms at all. In such cases, the condition is typically discovered when the individual has a physical examination.
Treatments for tachycardia
Treatment options vary, depending on what caused the condition, the patient's age and general health, and other factors. The aim of treatment is to address the cause of the tachycardia. When clinically applicable, the doctor may try to slow the rate, prevent subsequent episodes of tachycardia, and reduce risk complications.
In some cases, all that is required is to treat the cause. In other cases, no underlying cause is found, and the doctor may have to try out different therapies.
Ways to slow down a fast heartbeat
There are a variety of ways to treat tachycardia.
The vagal nerve helps regulate our heartbeat. Maneuvers that affect this nerve include coughing, heaving (as if you were having a bowel movement), and placing an ice pack on the patient's face.
Antiarrhythmic drugs can be administered orally (by mouth) or by injection; they restore a normal heartbeat. This is done in a hospital.
Available drugs restore normal heart rhythm, control the heart rate, or both. Sometimes a patient will need to take more than one antiarrhythmic drug.
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.
Prevention of episodes of tachycardia
Radiofrequency catheter ablation
Catheters enter the heart via blood vessels. Electrodes at the ends of the catheter are heated to ablate (damage) the small sections of the heart responsible for the abnormal heart beat.
When taken regularly, antiarrhythmic medications can prevent tachycardia. Patients may be prescribed other medications to be taken in combination with antiarrhythmics, for example, channel blockers, such as diltiazem (Cardizem) and verapamil (Calan), or beta-blockers, such as propranolol (Inderal), and esmolol (Brevibloc).
Implantable cardioverter defibrillator (ICD)
The device, which continuously monitors the patient's heartbeat, is surgically implanted into the chest. The ICD detects any heartbeat abnormality and delivers electric shocks to restore normal heart rhythm.
Sometimes, surgery is needed to remove a section of tissue. The surgeon may create a pattern 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.
Warfarin makes it harder for the blood to clot and is given to patients with a high or moderate risk of developing stroke or heart attack. Although Warfarin increases the risk of bleeding, it is prescribed for patients whose risk of stroke or heart attack is greater than their risk of bleeding.
Causes of tachycardia
Tachycardia is generally caused by a disruption in the normal electrical impulses that control our heart's pumping action - 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
Sometimes, the medical team may not identify the exact cause of the tachycardia.
Atria, ventricles, and the electrical circuitry of the heart
The heart consists of two ventricles and two atria.
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 heart has a natural pacemaker called the sinus node; it is located in the right atrium. The sinus node produces electrical impulses; each one triggers an individual heartbeat.
The electrical impulses leave the sinus node 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.
Types of tachycardia
The most common types of tachycardia include:
Sometimes, electrical activity can arise from the left atrium rather than the sinus node. This causes the chambers to contract at an excessively high and irregular rate; this is atrial fibrillation.
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.
The atria beat rapidly, but regularly. This is caused by a circuit problem within the right atrium. The contractions of the atria are weak because of the rapid heartbeat.
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 can also be caused by various forms of heart disease. Patients with atrial flutter commonly experience atrial fibrillation too.
Supraventricular tachycardias (SVTs)
This refers to any tachycardic (accelerated) heart rhythm originating above the ventricular tissue. The abnormal circuitry in the heart is usually congenital (present at birth) and creates a loop of overlapping signals. An SVT episode may last from a few seconds to several hours.
Abnormal electrical signals in the ventricles result in a rapid heart rate. The speed of the heartbeat 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.
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.
Risk factors for tachycardia
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 with 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
- Heart disease
- Hypertension (high blood pressure)
- Mental stress
- Using recreational drugs
Diagnosis of tachycardia
A doctor can usually diagnose tachycardia by asking the patient some questions regarding symptoms, carrying out a physical exam, and ordering some tests. These may include:
An electrocardiogram shows the electrical activity of the heart
Electrodes are attached to the patient's skin to measure electrical impulses given off by the heart.
This test will also show any previous heart disease that may have contributed to the tachycardia.
An echocardiogram is a type of ultrasound investigation. By bouncing sounds of the structures in the body and registering the echoes, a moving image of the heart can be produced. This can help look for structural or congenital abnormalities that might be playing a role in tachycardia.
These help determine whether thyroid problems or other substances may be factors contributing to the patient's tachycardia.
The patient wears a portable device that 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 their normal activities for 1 or 2 days.
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
This event recorder is good for diagnosing rhythm disturbances that happen at random moments.
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.
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 they are moved from a lying 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, this could explain the fainting spells, etc.
The X-ray images help the doctor check the state of the individual's heart and lungs. Other conditions that explain the tachycardia might also be detected.
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
The most common complications include:
- 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.