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Drugs That Affect the Cardiovascular System

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Drugs That Affect the Cardiovascular System PharmacologyPharmacologyPharmacology DrugsDrugs thatthat AffectAffect thethe CardiovascularCardiovascular SystemSystem TopicsTopicsTopics •• Electrophysiology Electrophysiology •• Vaughn-Williams Vaughn-Williams classificationclassification •• Antihypertensives Antihypertensives •• Hemostatic Hemostatic agentsagents CardiacCardiacCardiac FunctionFunctionFunction •• Dependent Dependent uponupon –– Adequate Adequate amountsamounts ofof ATPATP –– Adequate Adequate amountsamounts ofof CaCa++++ –– Coordinated Coordinated electricalelectrical stimulusstimulus AdequateAdequateAdequate AmountsAmountsAmounts ofofof ATPATPATP •• Needed Needed to:to: –– Maintain Maintain electrochemicalelectrochemical gradientsgradients –– Propagate Propagate actionaction potentialspotentials –– Power Power musclemuscle contractioncontraction AdequateAdequateAdequate AmountsAmountsAmounts ofofof CalciumCalciumCalcium •• Calcium Calcium isis ‘glue’‘glue’ that that linkslinks electricalelectrical andand mechanicalmechanical events.events. CoordinatedCoordinatedCoordinated ElectricalElectricalElectrical StimulationStimulationStimulation •• Heart Heart capablecapable ofof automaticityautomaticity •• Two Two typestypes ofof myocardialmyocardial tissuetissue –– Contractile Contractile –– Conductive Conductive •• Impulses Impulses traveltravel throughthrough ‘action‘action potentialpotential superhighway’.superhighway’. A.P.A.P.A.P. SuperHighwaySuperHighwaySuperHighway •• Sinoatrial Sinoatrial node node •• Atrioventricular Atrioventricular nodenode •• Bundle Bundle ofof HisHis •• Bundle Bundle BranchesBranches –– Fascicles Fascicles •• Purkinje Purkinje NetworkNetwork ElectrophysiologyElectrophysiologyElectrophysiology •• Two Two typestypes ofof actionaction potentialspotentials –– Fast Fast potentialspotentials •• Found Found in in contractile contractile tissue tissue –– Slow Slow potentialspotentials •• Found Found inin SA,SA, AVAV nodenode tissuestissues FastFastFast PotentialPotentialPotential Phase 1 +20 Phase 2 0 -20 Phase 3 -40 -60 Phase 4 -80 controlled by Na+ RMP channels = “fast channels” -80 to 90 mV FastFastFast PotentialPotentialPotential •• Phase Phase 0:0: NaNa++influxinflux “fast“fast sodiumsodium channels”channels” •• Phase Phase 1:1: KK ++effluxefflux •• Phase Phase 2:2: (Plateau)(Plateau) KK ++effluxefflux –– AND AND CaCa ++ + +influxinflux •• Phase Phase 3:3: KK++effluxefflux •• Phase Phase 4:4: RestingResting MembraneMembrane PotentialPotential CardiacCardiacCardiac ConductionConductionConduction CycleCycleCycle SlowSlowSlow PotentialPotentialPotential dependent upon Ca++ channels = “slow channels” 0 -20 Phase 4 Phase 3 -40 -60 -80 SlowSlowSlow PotentialPotentialPotential •• Self-depolarizing Self-depolarizing –– Responsible Responsible forfor automaticityautomaticity •• Phase Phase 44 depolarizationdepolarization –– ‘slow ‘slow sodium-calciumsodium-calcium channels’channels’ –– ‘leaky’ ‘leaky’ to to sodiumsodium •• Phase Phase 33 repolarizationrepolarization –K–K++effluxefflux CardiacCardiacCardiac PacemakerPacemakerPacemaker DominanceDominanceDominance •• Intrinsic Intrinsic firingfiring rates:rates: –SA–SA == 6060 –100–100 –– AV AV == 4545 –– 60 60 –– Purkinje Purkinje == 1515 -- 45 45 CardiacCardiacCardiac PacemakersPacemakersPacemakers •• SA SA isis primaryprimary –– Faster Faster depolarizationdepolarization raterate •Faster•Faster CaCa++++‘leak’‘leak’ •• Others Others areare ‘backups’‘backups’ –– Graduated Graduated depolarizationdepolarization raterate •• Graduated Graduated Ca Ca++++leakleak raterate PotentialPotentialPotential TermsTermsTerms RRP relative refractory period ERP effective refractory period APD action potential duration DysrhythmiaDysrhythmiaDysrhythmia GenerationGenerationGeneration •• Abnormal Abnormal genesisgenesis –– Imbalance Imbalance ofof ANSANS stimulistimuli –– Pathologic Pathologic phasephase 44 depolarizationdepolarization •• Ectopic Ectopic focifoci DysrhythmiaDysrhythmiaDysrhythmia GenerationGenerationGeneration •• Abnormal Abnormal conductionconduction •Analogies:•Analogies: –– One One wayway valvevalve –– Buggies Buggies stuckstuck inin muddymuddy roadsroads ReentrantReentrantReentrant CircuitsCircuitsCircuits Warning!Warning!Warning! •• All All antidysrhythmicsantidysrhythmics havehave arrythmogenicarrythmogenic propertiesproperties •• In In otherother words,words, theythey allall cancan CAUSECAUSE dysrhythmiasdysrhythmias too!too! AHAAHAAHA RecommendationRecommendationRecommendation ClassificationsClassificationsClassifications •• Describes Describes weightweight ofof •• ViewView AHAAHA definitionsdefinitions supportingsupporting evidenceevidence NOTNOT mechanismmechanism •• Class Class II •• Class Class IIaIIa •• Class Class IIbIIb •• Indeterminant Indeterminant •• Class Class IIIIII VaughnVaughnVaughn-Williams--WilliamsWilliams ClassificationClassificationClassification •• Class Class 11 •• Description Description ofof –Ia–Ia mechanismmechanism NOTNOT –Ib–Ib evidenceevidence –Ic–Ic •• Class Class IIII •• Class Class IIIIII •• Class Class IVIV •• Misc Misc ClassClassClass I:I:I: SodiumSodiumSodium ChannelChannelChannel BlockersBlockersBlockers •• Decrease Decrease NaNa++movementmovement inin phasesphases 00 andand 44 •• Decreases Decreases raterate ofof propagationpropagation (conduction)(conduction) viavia tissuetissue withwith fastfast potentialpotential (Purkinje)(Purkinje) –– Ignores Ignores thosethose withwith slowslow potentialpotential (SA/AV)(SA/AV) •• Indications: Indications: ventricularventricular dysrhythmiasdysrhythmias ClassClassClass IaIaIaAgentsAgents Agents •• Slow Slow conductionconduction •PDQ•PDQ:: throughthrough ventriclesventricles –– procainamide procainamide (Pronestyl®®) •• Decrease Decrease (Pronestyl ) repolarizationrepolarization raterate –– disopyramide disopyramide (Norpace(Norpace®®)) –– Widen Widen QRSQRS andand QTQT – qunidine intervalsintervals – qunidine – (Quinidex®®) •• MayMay promote promote Torsades Torsades – (Quinidex ) desdes Pointes! Pointes! ClassClassClass IbIbIbAgentsAgents Agents •• Slow Slow conductionconduction •• LTMD LTMD:: throughthrough ventriclesventricles –l–lidocaineidocaine (Xylocaine(Xylocaine®®)) •• Increase Increase raterate ofof –t–tocainideocainide (Tonocard (Tonocard®®)) repolarizationrepolarization –m–mexiletineexiletine (Mexitil (Mexitil®®)) – phenytoin (Dilantin®®) •• Reduce Reduce automaticityautomaticity – phenytoin (Dilantin ) –– Effective Effective forfor ectopicectopic focifoci •• May May havehave otherother usesuses ClassClassClass IcIcIcAgentsAgents Agents •• Slow Slow conductionconduction •• flecainide flecainide throughthrough ventricles,ventricles, (Tambocor(Tambocor®®)) atriaatria && conductionconduction •• propafenone propafenone systemsystem (Rythmol(Rythmol®®)) •• Decrease Decrease repolarizationrepolarization raterate •• Decrease Decrease contractilitycontractility •• Rare Rare lastlast chancechance drugdrug ClassClassClass II:II:II: BetaBetaBeta BlockersBlockersBlockers •Betareceptors in heart attached to Ca++++ •Beta11 receptors in heart attached to Ca channelschannels –Gradual–Gradual CaCa++++influxinflux responsibleresponsible forfor automaticityautomaticity •Betablockade decreases Ca++++influx •Beta11 blockade decreases Ca influx –– Effects Effects similarsimilar toto ClassClass IVIV (Ca(Ca++++channelchannel blockers)blockers) •• Limited Limited ## approvedapproved forfor tachycardiastachycardias ClassClassClass II:II:II: BetaBetaBeta BlockersBlockersBlockers •• propranolol propranolol (Inderal (Inderal®®)) •• acebutolol acebutolol (Sectral (Sectral®®)) •• esmolol esmolol (Brevibloc (Brevibloc®®)) ClassClassClass III:III:III: PotassiumPotassiumPotassium ChannelChannelChannel BlockersBlockersBlockers •• Decreases Decreases KK++effluxefflux duringduring repolarizationrepolarization •• Prolongs Prolongs repolarizationrepolarization •• Extends Extends effectiveeffective refractoryrefractory periodperiod •• Prototype: Prototype: bretylliumbretyllium tosylatetosylate (Bretylol(Bretylol®®)) –– Initial Initial norepinorepi dischargedischarge maymay causecause temporarytemporary hypertension/tachycardiahypertension/tachycardia –– Subsequent Subsequent norepinorepi depletiondepletion maymay causecause hypotensionhypotension ClassClassClass IV:IV:IV: CalciumCalciumCalcium ChannelChannelChannel BlockersBlockersBlockers •• Similar Similar effect effect as as ß ß •• verapamil verapamil (Calan (Calan®®)) blockersblockers •• diltiazem diltiazem (Cardizem (Cardizem®®)) •• Decrease Decrease SA/AVSA/AV automaticityautomaticity •• Decrease Decrease AVAV conductivityconductivity •• Note: Note: nifedipinenifedipine •• Useful Useful inin breakingbreaking doesn’tdoesn’t workwork onon heartheart reentrantreentrant circuit circuit •• Prime Prime side side effect: effect: hypotensionhypotension && bradycardiabradycardia Misc.Misc.Misc. AgentsAgentsAgents •• adenosine adenosine (Adenocard(Adenocard®®)) –– Decreases Decreases CaCa++++influxinflux && increasesincreases KK++effluxefflux viavia 22ndndmessengermessenger pathwaypathway •• Hyperpolarization Hyperpolarization of of membranemembrane •• Decreased Decreased conduction conduction velocity velocity via via slow slow potentials potentials •• No No effect effect on on fast fast potentials potentials •• Profound Profound sideside effectseffects possiblepossible (but(but short-short- lived)lived) Misc.Misc.Misc. AgentsAgentsAgents •• Cardiac Cardiac GlycocidesGlycocides •• digoxin digoxin (Lanoxin(Lanoxin®®)) –– Inhibits Inhibits NaKATPNaKATP pump pump –– Increases Increases intracellularintracellular
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