Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal or abnormal.
A 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 contraction of cardiac muscle in all animals is initiated by electrical impulses known as action potentials that in the heart are known as cardiac action potentials. The rate at which these impulses fire controls the rate of cardiac contraction, that is, the heart rate. The cells that create these rhythmic impulses, setting the pace for blood pumping, are called pacemaker cells, and they directly control the heart rate. They make up the cardiac pacemaker, that is, the natural pacemaker of the heart. In most humans, the highest concentration of pacemaker cells is in the sinoatrial (SA) node the natural and primary pacemaker, and the resultant rhythm is a sinus rhythm.
Fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibers. An important occurrence is with regard to the heart.
Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart.
The cardiac conduction system(CCS) transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through the body's circulatory system. The pacemaking signal travels through the right atrium to the atrioventricular node, along the bundle of His, and through the bundle branches to Purkinje fibers in the walls of the ventricles. The Purkinje fibers transmit the signals more rapidly to stimulate contraction of the ventricles.
Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower chambers of the heart. There are four main types of SVT: atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia (PSVT), and Wolff–Parkinson–White syndrome. The symptoms of SVT include palpitations, feeling of faintness, sweating, shortness of breath, and/or chest pain.
A junctional escape beat is a delayed heartbeat originating not from the atrium but from an ectopic focus somewhere in the atrioventricular junction. It occurs when the rate of depolarization of the sinoatrial node falls below the rate of the atrioventricular node. This dysrhythmia also may occur when the electrical impulses from the SA node fail to reach the AV node because of SA or AV block. It is a protective mechanism for the heart, to compensate for the SA node no longer handling the pacemaking activity, and is one of a series of backup sites that can take over pacemaker function when the SA node fails to do so. It can also occur following a premature ventricular contraction or blocked premature atrial contraction.
Premature atrial contraction (PAC), also known as atrial premature complexes (APC) or atrial premature beats (APB), are a common cardiac dysrhythmia characterized by premature heartbeats originating in the atria. While the sinoatrial node typically regulates the heartbeat during normal sinus rhythm, PACs occur when another region of the atria depolarizes before the sinoatrial node and thus triggers a premature heartbeat, in contrast to escape beats, in which the normal sinoatrial node fails, leaving a non-nodal pacemaker to initiate a late beat. The exact cause of PACs is unclear; while several predisposing conditions exist, single isolated PACs commonly occur in healthy young and elderly people. Elderly people that get PACs usually don't need any further attention besides follow ups due to unclear evidence. PACs are often completely asymptomatic and may be noted only with Holter monitoring, but occasionally they can be perceived as a skipped beat or a jolt in the chest. In most cases, no treatment other than reassurance is needed for PACs, although medications such as beta blockers can reduce the frequency of symptomatic PACs.
In cardiology, a ventricular escape beat is a self-generated electrical discharge initiated by, and causing contraction of the ventricles of the heart; normally the heart rhythm is begun in the atria of the heart and is subsequently transmitted to the ventricles. The ventricular escape beat follows a long pause in ventricular rhythm and acts to prevent cardiac arrest. It indicates a failure of the electrical conduction system of the heart to stimulate the ventricles.
Lorcainide is a Class 1c antiarrhythmic agent that is used to help restore normal heart rhythm and conduction in patients with premature ventricular contractions, ventricular tachycardiac and Wolff–Parkinson–White syndrome. Lorcainide was developed by Janssen Pharmaceutica (Belgium) in 1968 under the commercial name Remivox and is designated by code numbers R-15889 or Ro 13-1042/001. It has a half-life of 8.9 +- 2.3 hrs which may be prolonged to 66 hrs in people with cardiac disease.
Multifocal atrial tachycardia (MAT) is an abnormal heart rhythm, specifically a type of supraventricular tachycardia, that is particularly common in older people and is associated with exacerbations of chronic obstructive pulmonary disease (COPD). Normally, the heart rate is controlled by a cluster of cells called the sinoatrial node. When a number of different clusters of cells outside the SA node take over control of the heart rate, and the rate exceeds 100 beats per minute, this is called multifocal atrial tachycardia.
An ectopic pacemaker, also known as ectopic focus or ectopic foci, is an excitable group of cells that causes a premature heart beat outside the normally functioning SA node of the heart. It is thus a cardiac pacemaker that is ectopic, producing an ectopic beat. Acute occurrence is usually non-life-threatening, but chronic occurrence can progress into tachycardia, bradycardia or ventricular fibrillation. In a normal heart beat rhythm, the SA node usually suppresses the ectopic pacemaker activity due to the higher impulse rate of the SA node. However, in the instance of either a malfunctioning SA node or an ectopic focus bearing an intrinsic rate superior to SA node rate, ectopic pacemaker activity may take over the natural heart rhythm. This phenomenon is called an escape rhythm, the lower rhythm having escaped from the dominance of the upper rhythm. As a rule, premature ectopic beats indicate increased myocyte or conducting tissue excitability, whereas late ectopic beats indicate proximal pacemaker or conduction failure with an escape 'ectopic' beat.
Junctional ectopic tachycardia (JET) is a rare syndrome of the heart that manifests in patients recovering from heart surgery. It is characterized by cardiac arrhythmia, or irregular beating of the heart, caused by abnormal conduction from or through the atrioventricular node. In newborns and infants up to 6 weeks old, the disease may also be referred to as His bundle tachycardia or congenital JET.
Arrhythmias, 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. In more serious cases, there may be lightheadedness, passing out, shortness of breath or chest pain. While most cases of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure. Others may result in sudden death.
Bigeminy is a cardiac arrhythmia in which there is a single ectopic beat, or irregular heartbeat, following each regular heartbeat. Most often this is due to ectopic beats occurring so frequently that there is one after each sinus beat, or normal heartbeat. The two beats are figuratively similar to two twins. For example, in ventricular bigeminy, a sinus beat is shortly followed by a premature ventricular contraction (PVC), a pause, another normal beat, and then another PVC. In atrial bigeminy, the other "twin" is a premature atrial contraction (PAC).
Rotigaptide (ZP-123) is a drug under clinical investigation for the treatment of cardiac arrhythmias – specifically atrial fibrillation. It is a peptide analog that has been shown to increase gap junction intercellular conductance in cardiac muscle cells. Gap junctions are protein channels that are responsible for conducting electrical impulses between cells in the heart to maintain normal rhythm. Gap junction modulation is a promising and novel mechanism of action for the treatment of cardiovascular disorders. Its peptide sequence is Ac-D-Tyr-D-Pro-D-Hyp-Gly-D-Ala-Gly-NH2.
Premature junctional contractions (PJCs), also called atrioventricular junctional premature complexes or junctional extrasystole, are premature cardiac electrical impulses originating from the atrioventricular node of the heart or "junction". This area is not the normal but only a secondary source of cardiac electrical impulse formation. These premature beats can be found occasionally in healthy people and more commonly in some pathologic conditions, typically in the case of drug cardiotoxicity, electrolyte imbalance, mitral valve surgery, and cold water immersion. If more than two such beats are seen, then the condition is termed junctional rhythm. On the surface ECG, premature junctional contractions will appear as a normally shaped ventricular complex or QRS complex, not preceded by any atrial complex or P wave or preceded by an abnormal P wave with a shorter PR interval. Rarely, the abnormal P wave can follow the QRS.
A premature heart beat or extrasystole is a heart rhythm disorder corresponding to a premature contraction of one of the chambers of the heart. Premature heart beats come in two different types: premature atrial contractions and premature ventricular contractions. Often they cause no symptoms but may present with fluttering in the chest or a skipped beat. They typically have no long term complications.
An automatic tachycardia is a cardiac arrhythmia which involves an area of the heart generating an abnormally fast rhythm, sometimes also called enhanced automaticity. These tachycardias, or fast heart rhythms, differ from reentrant tachycardias in which there is an abnormal electrical pathway which gives rise to the pathology. Most automatic tachycardias are supraventricular tachycardias (SVT). It is important to recognise an automatic tachycardia because the treatment will be different to that for a reentrant tachycardia. The most useful clue will be the presence of 'warm up' and 'cool down'. This means that whereas a reentrant tachycardia will both begin and end abruptly as cardiac conduction utilises then ceases to utilise the accessory pathway, an automatic tachycardia will rise and fall gradually in rate as the automatic focus increases and decreases its automatic rate of electrical discharge.
