ArrhythmiaArrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults – is called tachycardia, and a resting heart rate that is too slow – below 60 beats per minute – is called bradycardia. Some types of arrhythmias have no symptoms. Symptoms, when present, may include palpitations or feeling a pause between heartbeats.
Electrophysiology studyA cardiac electrophysiology study (EP test or EP study) is a minimally invasive procedure using catheters introduced through a vein or artery to record electrical activity from within the heart. This electrical activity is recorded when the heart is in a normal rhythm (sinus rhythm) to assess the conduction system of the heart and to look for additional electrical connections (accessory pathways), and during any abnormal heart rhythms that can be induced.
Syncope (medicine)Syncope, commonly known as fainting, or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from low blood pressure. There are sometimes symptoms before the loss of consciousness such as lightheadedness, sweating, pale skin, blurred vision, nausea, vomiting, or feeling warm. Syncope may also be associated with a short episode of muscle twitching.
Ryanodine receptorRyanodine receptors (RyR for short) form a class of intracellular calcium channels in various forms of excitable animal tissue like muscles and neurons. There are three major isoforms of the ryanodine receptor, which are found in different tissues and participate in different signaling pathways involving calcium release from intracellular organelles. The RYR2 ryanodine receptor isoform is the major cellular mediator of calcium-induced calcium release (CICR) in animal cells.
Brugada syndromeBrugada syndrome (BrS) is a genetic disorder in which the electrical activity of the heart is abnormal due to channelopathy. It increases the risk of abnormal heart rhythms and sudden cardiac death. Those affected may have episodes of syncope. The abnormal heart rhythms seen in those with Brugada syndrome often occur at rest. They may be triggered by a fever. About a quarter of those with Brugada syndrome have a family member who also has the condition. Some cases may be due to a new genetic mutation or certain medications.
AdrenalineAdrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and by a small number of neurons in the medulla oblongata. It plays an essential role in the fight-or-flight response by increasing blood flow to muscles, heart output by acting on the SA node, pupil dilation response, and blood sugar level. It does this by binding to alpha and beta receptors.
Premature ventricular contractionA premature ventricular contraction (PVC) is a common event where the heartbeat is initiated by Purkinje fibers in the ventricles rather than by the sinoatrial node. PVCs may cause no symptoms or may be perceived as a "skipped beat" or felt as palpitations in the chest. PVCs do not usually pose any danger. The electrical events of the heart detected by the electrocardiogram (ECG) allow a PVC to be easily distinguished from a normal heart beat.
Cardiac stress testA cardiac stress test (also referred to as a cardiac diagnostic test, cardiopulmonary exercise test, or abbreviated CPX test) is a cardiological test that measures the heart's ability to respond to external stress in a controlled clinical environment. The stress response is induced by exercise or by intravenous pharmacological stimulation. Cardiac stress tests compare the coronary circulation while the patient is at rest with the same patient's circulation during maximum cardiac exertion, showing any abnormal blood flow to the myocardium (heart muscle tissue).
Atrial fibrillationAtrial fibrillation (AF or A-fib) is an abnormal heart rhythm (arrhythmia) characterized by rapid and irregular beating of the atrial chambers of the heart. It often begins as short periods of abnormal beating, which become longer or continuous over time. It may also start as other forms of arrhythmia such as atrial flutter that then transform into AF. Episodes can be asymptomatic. Symptomatic episodes may involve heart palpitations, fainting, lightheadedness, shortness of breath, or chest pain.
Cardiac arrestCardiac arrest occurs when the heart stops beating. It is defined as cessation of normal circulation of blood due to failure of the heart to pump effectively. It is a medical emergency that, without immediate medical intervention, will result in cardiac death within minutes. When it happens suddenly, it is called sudden cardiac arrest. Cardiopulmonary resuscitation (CPR) and possibly defibrillation are needed until further treatment can be provided. Cardiac arrest results in a rapid loss of consciousness, and breathing may be abnormal or absent.
