What is Tachycardia?
Tachycardia is the medical term for a heart rate that exceeds 100 beats per minutes (100 bpm). This is a higher than normal rate and may occur under temporarily during periods of stress, pain or strenuous activity. However, tachycardia may also be due to certain medical conditions and needs to be attended to as it will disrupt the normal blood pressure and strain the heart, possibly leading to cardiac arrest.
In adults, a heart rate of 60 to 100 beats per minute (bpm) is considered as normal. Most adults will have a heart rate of 65 to 85bpm. The heart rate can be assessed by measuring the pulse at the wrist (radial), elbow (brachial), neck (carotid), thigh (femoral), knee (popliteal), ankle (posterior tibial) or foot (dorsalis pedis).
How does tachycardia occur?
Impulses generated within the sinoatrial node (sinus node) of the heart is responsible for heart muscle contraction. These impulses travel via the internodal pathways to the atrioventricular node (AV node). A delay between the impulses to the atria and ventricles of the heart ensures that blood is pushed in cyclical manner between the chambers or out 0f the heart. It is the contraction of the ventricles that are felt as the pulse in the different areas of the body.
In tachycardia, one of the following disturbances may arise :
- Tachycardia may occur when there is an increased impulse generation emanating from the sinus node. This is referred to as increased automacity (sinus tachycardia).
- An increased heart rate may also occur when there is two pathways for an impulse to travel through but at different conducting rates. In this instance, the impulse from the slower conduit may travel backwards and into the other pathway. This is known as re-entry.
- Diseased heart tissue may hamper the proper depolarization and repolarization phases that are necessary for contraction and trigger a secondary contraction. This is known as triggered activity.
Types of Tachycardia
Tachycardia may be a supraventricular tachycardia or ventricular tachycardia.
In a supraventricular tachycardia (SVT), the rapid heartbeat stems from the atria and the flow of the blood into the ventricles are affected. Most types of tachycardia are SVT’s.
With ventricular tachycardia, the rapid heartbeat originates from the ventricles. This is serious and is often seen with life-threatening medical conditions like myocardial infarction (heart attack). Ventricular tachycardia can lead to cardiac arrest.
Symptoms of a Rapid Heart Rate
The following symptoms may arise due to tachycardia.
- Dizziness or fainting (extreme tachycardia)
- Chest pain or discomfort
- Shortness of breath (dyspnea)
In extreme cases, tachycardia can result in cardiac arrest may occur which can be fatal.
Causes of a Fast Pulse
- Heart disease
- Myocardial infarction (heart attack)
- Cardiac failure
- Chronic ischemic heart disease.
- Drugs – usually high doses of the following :
- Beta blockers
- Anti-arrhythmic drugs
- Antibiotics like erythromycin
- Anti-psychotic drugs
- Antimalarial drugs
- Lung diseases that affect perfusion, including infections like pneumonia and chronic obstructive pulmonary disorders (COPD)