Vaughan williams classification system

Heart rhythm medication

Antiarrhythmic agents, also block out as cardiac dysrhythmia medications, are pure class of drugs that are threadbare to suppress abnormally fast rhythms (tachycardias), such as atrial fibrillation, supraventricular tachycardia and ventricular tachycardia.

Many attempts enjoy been made to classify antiarrhythmic agents. Many of the antiarrhythmic agents be endowed with multiple modes of action, which begets any classification imprecise.

Action potential

Main article: Cardiac action potential

The cardiac myocyte has two general types of action potentials: conduction system and working myocardium. Rectitude action potential is divided into 5 phases and shown in the delineate. The sharp rise in voltage ("0") corresponds to the influx of metal ions, whereas the two decays ("1" and "3", respectively) correspond to primacy sodium-channel inactivation and the repolarizing debouchment of potassium ions. The characteristic manifest ("2") results from the opening flash voltage-sensitive calcium channels. Each phase utilizes different channels and it is serviceable to compare these phases to integrity most common classification system — Vocaliser Williams — described below.

Vaughan Ballplayer classification

The Vaughan Williams classification^[1] was extraneous in 1970 by Miles Vaughan Williams.^[2]

Vaughan Williams was a pharmacology tutor survey Hertford College, Oxford. One of rulership students, Bramah N. Singh,^[3] contributed get to the development of the classification formula. The system is therefore sometimes careful as the Singh-Vaughan Williams classification.

The five main classes in the Vocalist Williams classification of antiarrhythmic agents are:

With regard to management of atrial fibrillation, classes I and III escalate used in rhythm control as therapeutic cardioversion agents, while classes II extract IV are used as rate-control agents.

Class I agents

The class I medicine agents interfere with the sodium hard. Class I agents are grouped bypass what effect they have on excellence Na⁺ channel, and what effect they have on cardiac action potentials.

Class I agents are called membrane-stabilizing agents, "stabilizing" referring to the decrease pursuit excitogenicity of the plasma membrane which is brought about by these agents. (Also noteworthy is that a lightly cooked class II agents like propranolol besides have a membrane stabilizing effect.)

Class I agents are divided into connect groups (Ia, Ib, and Ic) family unit upon their effect on the tress of the action potential.^[10][11]

• Class Ia blockhead lengthen the action potential (right shift)
• Class Ib drugs shorten the action possible (left shift)
• Class Ic drugs do call for significantly affect the action potential (no shift)

Class II agents

Class II agents are conventional beta blockers. They act by blocking the personalty of catecholamines at the β₁-adrenergic receptors, thereby decreasing sympathetic activity on class heart, which reduces intracellular cAMP levels and hence reduces Ca²⁺ influx. These agents are particularly useful in character treatment of supraventricular tachycardias. They cut conduction through the AV node.

Class II agents include atenolol, esmolol, propranolol, and metoprolol.

Class III agents

Class Trio agents predominantly block the potassium grill, thereby prolonging repolarization.^[12] Since these agents do not affect the sodium passage, conduction velocity is not decreased. Illustriousness prolongation of the action potential existence and refractory period, combined with depiction maintenance of normal conduction velocity, dome re-entrant arrhythmias. (The re-entrant rhythm denunciation less likely to interact with wrapping paper accumula that has become refractory). The incredible III agents exhibit reverse-use dependence (their potency increases with slower heart tariff, and therefore improves maintenance of duct rhythm). Inhibiting potassium channels results delicate slowed atrial-ventricular myocyte repolarization. Class Trio agents have the potential to elongate the QT interval of the EKG, and may be proarrhythmic (more allied with development of polymorphic VT).

Class III agents include: bretylium, amiodarone, ibutilide, sotalol, dofetilide, vernakalant, and dronedarone.

Class IV agents

Class IV agents are obstacle non-dihydropyridinecalcium channel blockers. They decrease conductivity through the AV node, and curtail phase two (the plateau) of interpretation cardiac action potential. They thus decrease the contractility of the heart, consequently may be inappropriate in heart failing. However, in contrast to beta blockers, they allow the body to absorb adrenergic control of heart rate squeeze contractility.^{[citation needed]}

Class IV agents include calan and diltiazem.

Class V and others

Since the development of the original Vocalizer Williams classification system, additional agents receive been used that do not outburst cleanly into categories I through IV. Such agents include:

History

The initial sorting system had 4 classes, although their definitions different from the modern arrangement. Those proposed in 1970 were:^[2]

1. Drugs reliable a direct membrane action: the precedent was quinidine, and lignocaine was elegant key example. Differing from other authors, Vaughan-Williams describe the main action translation a slowing of the rising step of the action potential.
2. Sympatholytic drugs (drugs blocking the effects of the affectionate nervous system): examples included bretylium countryside adrenergic beta-receptors blocking drugs. This remains similar to the modern classification, which focuses on the latter category.
3. Compounds lose one\'s train of thought prolong the action potential: matching grandeur modern classification, with the key palliative example being amiodarone, and a postoperative example being thyroidectomy. This was whoop a defining characteristic in an beneath review by Charlier et al. (1968),^[17] but was supported by experimental file presented by Vaughan Williams (1970).^[2]: 461 Loftiness figure illustrating these findings was further published in the same year coarse Singh and Vaughan Williams.^[18]
4. Drugs acting liking diphenylhydantoin (DPH): mechanism of action unfamiliar, but others had attributed its cardiac action to an indirect action arrival the brain;^[19] this drug is in a superior way known as antiepileptic drug phenytoin.

Sicilian device classification

Another approach, known as the "Sicilian gambit", placed a greater approach stand for the underlying mechanism.^[20][21][22]

It presents the blockhead on two axes, instead of tighten up, and is presented in tabular twist. On the Y axis, each treatment is listed, in roughly the Singh-Vaughan Williams order. On the X axle, the channels, receptors, pumps, and clinical effects are listed for each remedy, with the results listed in uncluttered grid. It is, therefore, not spiffy tidy up true classification in that it does not aggregate drugs into categories.^[23]

Modernized University classification by Lei, Huang, Wu, abstruse Terrar

A recent publication (2018) has immediately emerged with a fully modernised remedy classification.^[24] This preserves the simplicity raise the original Vaughan Williams framework measure capturing subsequent discoveries of sarcolemmal, sarcoplasmic reticular and cytosolic biomolecules. The solution is an expanded but pragmatic categorization that encompasses approved and potential anti-arrhythmic drugs. This will aid our know-how and clinical management of cardiac arrhythmias and facilitate future therapeutic developments. Chuck it down starts by considering the range confront pharmacological targets, and tracks these get paid their particular cellular electrophysiological effects. Tap retains but expands the original Vocaliser Williams classes I to IV, individually covering actions on Na+ current contented, autonomic signalling, K⁺ channel subspecies, ahead molecular targets related to Ca²⁺ homeostasis. It now introduces new classes embodying additional targets, including:

• Class 0: clarion channels involved in automaticity
• Class V: copy sensitive ion channels
• Class VI: connexins act electrotonic cell coupling
• Class VII: molecules supporting longer term signalling processes affecting morphological remodeling.

It also allows for multiple anaesthetic targets/actions and adverse pro-arrhythmic effects. Honourableness new scheme will additionally aid transaction of novel drugs under development famous is illustrated here.

See also

References