unit 6.2 antidysrhyt chapter 26 antidysrhythmic drugs

Term Definition
Action potential electrical activity that consists of polarization and depolarization and that travels across the cell membrane of a nerve fibre during transmission
action potential duration (APD) the interval beginning with the baseline membrane potential, followed by depolarization, and ending with depolarization to baseline membrane poten
arrhythmia "without rhythm" absence of a heart rhythm. more commonly used in clinical practice to refer to any variation from normal rhythm
asystole state of no cardiac electrical activity in the heart
atrial fibrillation rapid atrial contraction shot incompletely pump blood into the ventricles
cardiac arrhythmia suppression trial (CAST) major research study conducted to investigate possibility of eliminating sudden cardiac death in patients with asymptomatic ectopy after MI
cardioversion procedure by which an abnormally fast heart rate or cardiac dyrthythmia is converted to normal rhythm using electricity or drugs
depolarization the movement of positive and negative ions on either side of a cell membrane across the membrane in a direction that brings the net charge to zero
dysrhythmia any disturbance or abnormality in the rhythm of the heartbeat
effective refractory period (ERP) the period after the firing of an impulse during which a cell may respond to a stimulus but the response will not be passed along or continued as impulse
internal pathways (Bachmann's bundle) special pathways in the atria that carry electrical impulses spontaneously generated by the SA node. they cause the heart to beat
relative refractory period (RRP) the time after generation of an action potential during which a nerve fibre will show response only to strong stimulations
resting membrane potential (RMP) the voltage that exists when the cell membranes of heart muscle are at rest
sodium-potassium adenosine triphosphate (ATPase) pump mechanism or transporting sodium and potassium ions across the cell membrane against an opposing concentration gradient
sudden cardiac death unexpected fatal cardiac arrest
threshold potential the critical state of electrical tension require for spontaneous depolarization of a cell membrane
torsades de pointes rare ventricular dysrhythmia that is associate with long QT interval and can degenerate into ventricular fibrillation and sudden death
vaughan williams classification the system most commonly used to classify antidysrhythmic drugs
ventricular tachycardia a rapid heartbeat from impulses originating in there ventricles
technically the term arrhythmia implies asystole (no heartbeat)
disturbances in arrhythmias are the result of abnormally functioning cardiac cells
polarized distribution of extracellular sodium and calcium ions and intracellular potassium CL and Bicarb maintained by sodium potassium adenosine triphosphate (ATPase) pump
action potential has ____ phases 5
Phase 0 also called the upstroke – resting cardiac cell membrane suddenly becomes highly permeable to sodium ions which go from OUTSIDE TO INSIDE
depolarization can be thought of as temporary equalization of positive and negative charges across the cell membrane
Phase 1 a rapid period of depolarization – sodium changes close and the concentrations of each ion begin to move back toward their ion RMP level
phase 4 RMP (resting membrane potential)
Phase 2 calcium channels called slow channels because the calcium influx occurs more slowly than sodium influx
the level of RMP for a given type of cell is an important determinant of the rate of its impulse conduction to other cells – less negative the slower is the upstroke velocity of phase 0
the slope of phase 0 is directly related to the impulse velocity
steeper slow indicates faster conduction velocity
Pirkinje cells electrical conduction is relatively fast and therefore impulses are conducted quickly
Purkinje cells are referred to as fast responce cells or fast-channel cells
many antidysrhythmics affect the RMP and sodium channels which in turn influence the rate of impulse conduction
the cells of the SA node have a slower upstroke velocity or a slower phase 0
AV node cells conduction velocity is comparable to SA nodal cells velocity
the slower upstroke in the SA and AV nodes is primarily dependent on the entry of calcium ions through the slow changes or calcium channes
effective refractory period is the period from Phase 0 – midway phase 3
action potential duration is the phase between phase 0 and phase 4
the SA node is the natural pacemaker of the heart because it sponatanously depolarizes the most frequently
the SA had an intrinsic rate of 60-100 depolarizations per minute
the AV node has an intrinsic rate of 40-60 depolarizations per minute
the ventricular Purkinje fibres has an intrinsic rate of 40 or fewer beats per minute
supra ventricular dysrhythmias origninate above the ventricles in the SA or AB node or atrial myocardium
ventricular dysrhythmias originate below the AG node in the HIs-Purkinje system or ventricular myocardium
Dysrhythmias that originate outside the conduction system are considered ectopic and their specific point of origin are called ectopic foci
conduction block are dysrhythmias that involve disruption of impulse induction between the atria and ventricles through the AV node directly affecting ventricular function
atrial fibrillation is notable in that it
paroxysmal superaventricular tachycardia AV nodal re-entrant tachycardia – a conduction disorder that gives rise to this tachycardi
class III drugs amiodaron, dronedarone, stall, ibutilide – the most widely used antidysrhythmics
class IV drugs (calcium chanel blockers) have limited usefulness in tachydysrhythmias
Class I drugs are membrane stabilizing drugs that expert their action on sodium (fast) channels
class II drugs are B-adrenergi blockers and commonly used as hypertensives
class III drugs (amiodoraon, dronedarone, stall, and ibutilide) action increase the APD (action potential depolarization ) by prolonging depolarization in phase 3 – also considered CALCIUM CHANNEL BLOCKERS
class IV drugs are considered calcium channel blockers similar to B-blockers – used as antianginal drugs and antihypertensives

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