Antiarrhythmic Drugs
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Transcript of Antiarrhythmic Drugs
ANTIARRHYTHMIC DRUGS
Moderator: Prof G.P. SinghPresented by: Dr Rajesh Raman
& Dr Ravi Prakash
Mechanism of arrhythmias
reduced (morepositive) resting membrane potential bringing it closer to the threshold potential
Ischemia and electrolyte imbalances
2 0 depolarization originate duringphase 2 or 3 of the action potential
originating from phase 4
circulation of an activation wave around an inexcitable obstacle
Abnormal generation of impulses
Types of Cardiac Arrhythmias
Sinus arrhythmia (cyclic changes in heart rate during breathing)
Sinus tachycardia (the SA node emits impulses faster than normal)
Sick sinus syndrome (the SA node fires improperly)
Premature supraventricular contractions (a premature impulse initiation in the atria causes the heart to beat prior to the time of the next normal heartbeat)
Supraventricular tachycardia (early impulse generation in the atria speed up the heart rate)
Atrial flutter (rapid firing of signals in the atria cause atrial myocardial cells to contract quickly, leading to a fast and steady heartbeat)
Atrial fibrillation (electrical impulses in the atria are fired in a fast and uncontrolled manner, and arrive in the ventricles in an irregular fashion)
Wolff-parkinson-white syndrome (abnormal conduction paths between the atria and ventricles cause electrical signals to arrive in the ventricles too early, and subsequently reenter the atria)
Supraventricular arrhythmias
…Types of Cardiac Arrhythmias
Premature ventricular complexes (electrical signals from the ventricles cause an early heartbeat, after which the heart seems to pause before the next normal contraction of the ventricles occurs);
Ventricular tachycardia (increased heart rate due to ectopic signals from the ventricles);
Ventricular fibrillation (electrical impulses in the ventricles are fired in a fast and uncontrolled manner, causing the heart to quiver).
Ventricular arrhythmias
Vaughan Williams'
Class Electrophysiology Examples I. Na-Channel Blockers Ia. phase 0
conduction v repolarisation APD
quinidine disopyramide procainamide
Ib. phase 0 conduction v repolarisation APD
lignocaine phenytoin tocainide, mexiletine
Ic. phase 0 conduction v repolarisation APD
flecanide ecainide, lorcainide
II. blockers propranolol atenolol, esmolol
III. Prolong Repolarisation (usually by K+ channel block)
repolarisation amiodarone bretylium, sotalol
IV. Calcium Entry Blockers
verapamil diltiazem
fast inflow ofNa+ ions
Outflow of k+ ions
Slow inflow of Ca++ outflow of K+
Fast outflow of K+
fully repolarised state
Na+ channel blockerβ-blockers
K+ channel blockers
Ca++ channel blockers
Antiarrhythmic Drug Actions
Most of anti arrhythmic drugs have actions which can be attributed to more than one class
Drugs unclassified in the Vaughan Williams system
SODIUM CHANNEL BLOCKERSCLASS I
Bind to sodium channels and inhibit or block sodium conductance
Decrease in the rate of rise of phase 0 of the cardiac membrane action potential and a slowing of the conduction velocity
Suppress both normal purkinje fiber and his bundle automaticity in addition to abnormal automaticity resulting from myocardial damage
Bind more rapidly to open or inactivated sodium channels than to channels that are fully repolarized
Greater degree of blockade in tissues that are frequently depolarizing
ERP of fast-response fibers is prolonged These can depress myocardium at high doses
Reduce rate of phase 4 depolarization in automatic cells
Classification
These have been divided into 3 classes on basis of quantitative rates of drug binding to, and dissociation from, sodium ion channels
• IB : interact rapidly with Na channel
• IC: interact slowly• IA: intermediate
Class IA agents
Include Quinidine, procainamide and disopyramide Intermediate kinetics of binding and dissociation Combined sodium and potassium channel blockade Moderate phase 0 depression and conduction
slowing, prolonging of action potential duration by blocking outward K+ current
Blockade is greater in cells with greater frequency of depolrization
Block Na channel conduction QRS duration Block K channel action potential duration QT interval effective refractory period
IA
Quinidine
Prototype class IA drug. Slows the rapid upstroke during phase 0
and decreases the slope of phase 4 spontaneous depolarization.
In circuit loops in purkinje fibres, quinidine frequently converts one-way conduction block into two-way block, thus abolishing the reentry circuit
Electrocardiographic Changes
Quinidine prolongs the PR, the QRS, and the QT intervals
Hemodynamic Effects
In patients with compromised myocardial function, quinidine may depress cardiac contractility sufficiently to result in a decrease in cardiac output, a significant rise in left ventricular end-diastolic pressure, and overt heart failure. Can relax vascular smooth muscle directly as well as indirectlyQuinidine produces adrenergic receptor blockade and vagal inhibition. Thus the intravenous use of quinidine is associated with marked hypotension and sinus tachycardia
Clinical Uses
(1)Abolition of premature complexes that have an atrial,
A-V junctional, or ventricular origin;(2)Restoration of normal sinus rhythm in atrial flutter
and atrial fibrillation after controlling the ventricular rate with digitalis;
(3)Maintenance of normal sinus rhythm after electrical conversion of atrial arrhythmias;
(4)Prophylaxis against arrhythmias associated with electrical countershock;
(5) Termination of ventricular tachycardia; and (6) Suppression of repetitive tachycardia associated
with wolff- parkinson-white (WPW) syndrome.
Because of the high incidence of ventricular proarrhythmia associated with its use and numerous other equally efficacious agents, quinidine is now used sparingly
Procainamide
Derivative of the local anaesthetic procaine Longer half-life, does not cause CNS toxicity
at therapeutic plasma concentrations, and is effective orally
Slows phase 0 & impulse conduction Increased ERP, APD, QRS and QT interval Procainamide is a particularly useful
antiarrhythmic drug, effective in the treatment of supraventricular, ventricular, and digitalis-induced arrhythmias
Adverse effects
With chronic use, it causes a reversible lupus erythematosus-like syndrome
CNS side effects include depression, hallucination and psychosis.
Gastrointestinal intolerance is less frequent than with quinidine.
Toxic concentrations of procainamide may cause asystole or induction of ventricular arrhythmias.
The intravenous route is rarely used because hypotension occurs if the drug is too rapidly infused.
USES
Terminate monomorphic VT Prevent recurrence of VF but is rarely
used for chronic therapy due to high incidence of lupus like syndrome
Disopyramide
Negative inotropic effect that is greater than the weak effect exerted by quinidine and procainamide, and unlike the latter drugs, disopyramide causes peripheral vasoconstriction.
No effect on sinus rate Less prolonged PR & QRS broadening Used for treatment of ventricular arrhythmias as
an alternative to procainamide or quinidine. 2nd line drug for prevention of recurance of VT/VF Maintaince therapy after cardioversion of AF/AFl Disopyramide shows effects of anticholinergic activity,
for example, dry mouth, urinary retention, blurred vision, and constipation.
CLASS IB
Lidocaine, mexiletine, tocainide, phenytoin
Pure sodium channel blockers Decrease the duration of action potential
and ERP of purkinje fibres Minimal effect on the rate of depolarization Minimal effect on conduction velocity in
ventricular myocardium Ib
Associate and dissociate rapidly within the timeframe of the normal heartbeat with channel recovery time < 1 second
Binds to open channels during phase 0 of the action potential (affecting the rate of rise very little, but leaving many of the channels blocked by the time the action potential reaches its peak)
Dissociation occurs in time for the next action potential
A premature beat, however, will be aborted because the channels are still blocked
Bind selectively to refractory channels and thus block preferentially when the cells are depolarised, for example in ischaemia.
Lignocaine
Unlike quinidine or procainamide, most of its effects on the heart are by direct action No important interactions with the ANS
Causes suppression of automaticity of ectopic foci but SA node is not depressed Enhanced phase 4 depol. in partially depol. purkinje fibers
and delayed after depolarizations are antagonized Almost no change in the APD of normal specialised
atrial fibres Substantially decreases APD in purkinje fibres and
ventricular muscle The ERP is also shortened but not to the same degree
as the APD, \'s ERP:APD ratio
Lignocaine and Reentry
Can abolish ventricular reentry, either by, Establishing 2-way conduction blockade
Eg. Ischemia Improving conduction
Eg. Low [k]o
Much less effective than quinidine or procainamide in slowing the atrial rate in AF or flutter, or in converting these to SR In keeping with minimal effects on atrial
tissue
Lignocaine & ECG
In striking contrast to quinidine or procainamide, lignocaine causes little or no change in the ECG
The Q-T interval may shorten, but the QRS does not widen
Usually no change in the refractory period of the AV node This may be shortened in some patients, who
show an increased ventricular rate in AF In patients with bundle branch disease, lignocaine
may cause complete AV block within the H-P system
Lignocaine: Kinetics
Well absorbed after oral administration Subject to extensive first pass metabolism
®Bioavailability ~ 33% Almost completely absorbed after IM
administration Kinetics after IV administration follow a two
compartment model Distribution half-life t½a ~ 8 mins
Elimination half-life t½b ~ 100 mins
Lignocaine: Interactions
Negative inotropic action may be potentiated by, Disturbances of acid-base, or electrolyte
balance
Hypoxia
Other myocardial depressant drugs
Pre-existing myocardial disease
Uses
Treating ventricular arrhythmias arising during myocardial ischemia
Drug of choice for treatment of the electrical manifestations of digitalis intoxication
Used prophylactically in MI to prevent VF
Adverse effects
One of the least toxic antiarrhythmic Mainly due to its actions on the central
nervous system and include drowsiness, disorientation and convulsions
Tocainide.
Analogue of lidocaine Mechanism of action that is similar to
lidocaine It is orally active Used to prevent or treat ventricular
tachycardias Tocainide can lead to pulmonary fibrosis.
Mexiletine.
Resembles lidocaine and tocainide Orally active Effects on cardiac electrophysiology are
similar to that of lidocaine Used in the treatment of ventricular
arrhythmias, however, due to proarrhythmic side effects; it is generally not used with less severe arrhythmias
Effective in post MI ventricular arrhythmias as alternative to lidocaine resistant cases
Class IC
Associate and dissociate with sodium channels much more slowly
Most potent sodium channel blockers They reach a steady-state level of block that does not
vary appreciably during the cardiac cycle; they also show only a marginal preference for refractory channels, so are not specific for damaged myocardium.
Cause a rather general reduction in excitability and do not discriminate particularly against occasional premature beats
Significantly prolong the refractory period within the AV node and in accessory bypass tracts
Have minimal effects on the APD Used to prevent supraventricular arrhythmias in
patients who have otherwise structurally normal hearts High pro-arrhythmic potential
Ic
Propafenone
Its major electrophysiological effect is to slow conduction in fast-response tissues
Propafenone prolongs PR and QRS durations Like other Na+ channel blockers, it also can be
used in ventricular arrhythmias, but with only modest efficacy.
It has β-blocking properties and can aggravate congestive heart failure and
Chronic therapy with oral propafenone is used to maintain sinus rhythm in patients with supraventricular tachycardias, including atrial fibrillation
FLECAINIDE
Potent blocker of sodium and potassium channels with slow unblocking kinetics
Used for patients with otherwise normal hearts who have supraventricular arrhythmias.
Flecainide has a negative inotropic effect and can aggravate congestive heart failure.
It is used orally to suppress and prevent the recurrent of documented life-threatening ventricular arrhythmias and supraventricular tachyarrhythmias in patients not associated with CHF
Encainide
Used orally to suppress and prevent recurrence of documented life-threatening ventricular arrhythmias
β-adrenoceptor antagonists Class II drugs:
β-adrenoceptor antagonists
Ventricular dysrhythmias following myocardial infarction are partly the result of increased sympathetic activity, providing a rationale for using β-adrenoceptor antagonists in this setting
AV conduction depends critically on sympathetic activity; β-adrenoceptor antagonists increase the refractory period of the AV node and can therefore prevent recurrent attacks of SVT
These decrease slope of phase 4 depolrization and automaticity in SA node, Purkinje fibers & other ectopic foci, only when this has been increased under adrenergic action
The β-adrenoceptor antagonists are used to prevent paroxysmal attacks of atrial fibrillation when these occur in the setting of sympathetic activation.
Also frequently used to slow the ventricular rate in atrial flutter and fibrillation by impairing conduction and increasing the refractoriness of the AV node
The β -blockers must be tapered off gradually for 1 week.
Propranolol
Propranolol is a non-selective β-antagonist Effective in attenuating supraventricular
cardiac arrhythmias but are generally not effective against ventricular arrhythmias (except those induced by exercise)
Propranolol reduces the incidence of sudden arrhythmic death after myocardial infarction
Adverse effects include: Bronchoconstriction, hypoglycemia, Na+ retention, Sexual impairment
Uses
Sinus Tachycardia Atrial & nodal extrasystole evoked by
exercise/emotion PSVT Control ventricular rate in AF/A Fl Reduces digitalis induced tachyarrhythmias Arrhythmias associated with
Pheochromocytoma and halothane anaesthesia
Esmolol
Short-acting β blocker used primarily as an antiarrhythmic drug for intraoperative and other acute arrhythmias
Preferentially blocks the β1 receptors Esmolol’s electrophysiological actions are similar
to those of propranolol. Esmolol decreases arterial pressure, heart rate,
ventricular contractility, and pulmonary vascular resistance.
Treatment of supraventricular tachyarrhythmias for rapid control of ventricular rate and reduction of myocardial oxygen consumption
CLASS III Agents Prolonging
Repolarisation
CLASS III
These drugs substantially prolong the cardiac action potential usually by K+ channel block
Action potential prolongation is least marked at fast rates (where it is desirable) and most marked at slow rates
Action potential prolongation increases the refractory period(tissue remains refractory even after full repolarization) , accounting for powerful and varied antidysrhythmic activity, for example by interrupting re-entrant tachycardias and suppressing ectopic activity
Can cause torsade de pointes
AMIODARONE
Amiodarone
Class III antiarrhythmic agent effective orally & IV in the treatment of ventricular and atrial arrhythmias
Analogue of thyroid hormone Prolongs APD and ERP, of atrial, nodal
and ventricular tissues Explains its broad spectrum of activity
Decreases automaticity in the SA node by reducing the slow phase 4 depolarization
Inhibits myocardial Ca++ channels and has β blocking properties
….Amiodarone
The ERP of atrial fibres is responsible for its effectiveness in SVTs
Decreases the conduction velocity and increases the ERP of the AV node, both anterograde and retrograde, making it particularly useful for reentry phenomena
ERP of His Purkinje and myocardial fibres
Minimal effect on SA node
…..Amiodarone
Oral absorption is incomplete and erratic, bioavailability ~ 22-86%
Half life is long: t½b ~ 14-59 days Drug accumulates in adipose and highly
perfused tissues Pharmakokinetics after IV administration
differ markedly Removal being relatively rapid, t½ ~ 20
hrs, due to redistribution
Amiodarone Toxicity
N & V - rarely constipation abnormal LFT's abnormal TFT's
¯'s peripheral conversion T4 ® T3
¯'s conversion in the pituitary ® TSH levels both hyper & hypothyroidism may occur and the onset may be
abrupt cardiovascular effects : *usually minimal
atypical VT - Torsade de pointes bradycardia rarely exacerbation of CCF
photosensitive skin rashes corneal micro-deposits pneumonitis & interstitial pulmonary fibrosis
Amiodarone - Drug Interactions Digoxin - potential severe bradycardia B-blockers - potential severe bradycardia Ca-antagonists - potential severe bradycardia
Disopyramide - long QT syndrome Quinidine - long QT syndrome & atypical VT Mexiletine - long QT syndrome
Procainamide - serum levels significantly increased Warfarin - inhibits metabolism
Sotalol
It is a nonselective β adrenergic receptor antagonist that also prolongs cardiac action potentials by inhibiting K+ currents
Sotalol prolongs action potential duration throughout the heart and QT interval on the ECG
It decreases automaticity, slows AV nodal conduction, and prolongs AV refractoriness by blocking both K+ channels and β adrenergic receptors, but it exerts no effect on conduction velocity in fast-response tissue
Sotalol is approved for use in patients with both ventricular tachyarrhythmias and atrial fibrillation or flutter.
The most serious side effect is torsade de pointe, the QTc interval must be watched carefully for excess prolongation
Dofetilide
Orally active Selectively blocks K+ current: pure class
antiarrhythmic Used to maintain and convert AF/Afl to
sinus Rhythm
Ibutilide
Newer class III antiarrhythmic used to convert AF/AFl to sinus rhythm
Ca2+ channel blockersClass IV
Selective blockade of the slow L-type cardiac calcium channels
They are most potent in tissues in which the action potential depends on calcium currents, such as the SA and AV nodes
Within nodal tissue, calcium channel blockade elevates the threshold potential, decreases the rate of rise of phase 0 depolarization and conduction velocity, and lengthens the refractory period of the AV node
Clinical effects caused are: The heart rate slows; transmission of rapid atrial impulses through the AV node
to the ventricles decreases, thus slowing the ventricular rate in atrial fibrillation and atrial flutter; and
reentrant rhythms traveling through the AV node may terminate
Used in treatment of reentrant PSVT, to slow the ventricular rate in patients with atrial fibrillation or flutter.
Verapamil
Verapamil
A derivative of papaverine and was first used as a coronary vasodilator
Produces Ca++-channel blockade in cardiac and smooth muscle membranes
Substantially slows the rate of impulse formation in the SA node in vitro
However, this is offset in vivo due to reflex SNS activity resulting from arteriolar vasodilation
Normally the rate slows ~ 10-15%
Verapamil
No significant effects on intra-atrial conduction
Rate of phase 4 depolarisation in H-P fibres Can block delayed ADP's and triggered activity
resulting from digitalis toxicity Most marked effect of verapamil is on the AV
node conduction velocity & ERP
Results directly from ca++-channel blockade However is not seen at usual therapeutic
concentrations of other Ca++-channel blockers, eg. Nifedipine
Uses:
To prevent recurrence of paroxysmal supraventricular tachycardia (SVT)
To reduce the ventricular rate in patients with atrial fibrillation, provided they do not have wolff-parkinson-white or a related disorder.
Diltiazem
Similar to verapamil but has relatively more smooth muscle-relaxing effect and produces less bradycardia.
Diltiazem is effective in controlling the ventricular rate in patients with atrial flutter or atrial fibrillation
OTHER ANTIARRHYTHMICS
CARDIAC GLYCOSIDES: Digoxin
Digoxin shortens the refractory period in atrial and ventricular myocardial cells while prolonging the effective refractory period and diminishing conduction velocity in Purkinje fibers.
bind specifically to the Na+/K+-ATP'ase, inhibit its enzymatic activity
Digoxin enhances the inotropic state by increasing the intracellular calcium concentration
Used to treat and prevent sinus and supraventricular fibrillation, flutter, and tachycardia
Adenosine
Most of the purine agents have acute vasodilating properties in most vascular beds
Adenosine is an important autocoid and endogenous vasodilator in man
Decreases conduction velocity, prolongs the refractory period, and decreases automaticity in the AV node.
Adenosine has an extremely short duration of action (about 15 seconds).
Adenosine - Actions
Termination of PSVT Demonstrated safely and effectively in older children
and adults Induced hypotension Direct negative inotropic effect Coronary blood flow increases Pulmonary vascular resistance decreases but not
to the same extent as SVR Decreased GFR in the kidney
Atropine
Atropine shortens AV node ERP and increases conduction velocity in bundle of his
When A-V block is due to vagal overactivity, eg. Digitalis toxicity, it can be overcome by atropine
Sympathomimetics
Adrenaline and isoprenaline can overcome partial heart block by facilitating AV Conduction and shortening ERP of conducting tissues
SUMMARY: ANTIARRHYTHMIC DRUGS
Antiarrhythmic Therapy
Patient-Specific Contraindications
CONDITION EXCLUDE/USE WITH CAUTION
Cardiac Heart failure Disopyramide, flecainide Sinus or AV node Digoxin, verapamil, dil-dysfunction tiazem, β adrenergic
receptor antagonists, amiodarone
Wolff–Parkinson–White Digoxin, verapamil, syndrome (risk of diltiazem extremely rapid rate if atrial fibrillation develops) Infranodal conduction Na+ channel blockers, disease amiodarone Aortic/subaortic stenosis Bretylium History of myocardial Flecainide infarction Prolonged QT interval Quinidine, procainamide,
disopyramide, sotalol, dofetilide, ibutilide, amiodarone
Cardiac transplant Adenosine
CONDITION EXCLUDE/USE WITH CAUTION
Noncardiac Diarrhea Quinidine Prostatism, glaucoma Disopyramide Arthritis Chronic procainamide Lung disease Amiodarone Tremor Mexiletine, tocainide
Constipation Verapamil Asthma, peripheral vas- β Adrenergic blockers, cular disease, propafenone hypoglycemia
Sinus Bradycardia
Heart rates lower than 40 beats/min are poorly tolerated, even in healthy patients, and should be evaluated on the basis of their effect on cardiac output
Treatment is recommended if hypotension, ventricular arrhythmias, or signs of poor peripheral perfusion are observed
When treatment is deemed necessary, the following approach may be considered
atropine, 0.5 to 1.0 mg by intravenous bolus repeated every 3 to 5 minutes, up to 0.04 mg/kg
ephedrine, 5 to 25 mg by intravenous bolus; dopamine or dobutamine (if blood pressure is
adequate), 5 to 20 µg/kg/min by intravenous infusion;
epinephrine, 2 to 10 µg/min by intravenous infusion;
isoproterenol, 2 to 10 µg/min by intravenous infusion.
Temporary transcutaneous or transvenous pacing may be necessary for severe, drug-refractory sinus bradycardia
Sinus Tachycardia
Prolonged tachycardia in patients with underlying heart disease can precipitate MI and congestive heart failure (CHF) as a result of the increased myocardial work required and decreased myocardial oxygen supply because of decreased diastolic coronary perfusion time
The underlying disorder should be treated. Hypovolemia and light anesthesia are the most common causes. In patients with ischemic heart disease in whom tachycardia develops, β-adrenergic blockers should be used judiciously to prevent myocardial ischemia regardless of whether ST-segment changes are present.
Paroxysmal Supraventricular Tachycardia
When a patient is anesthetized, PSVT can be precipitated by changes in autonomic nervous system tone, by drug effects, or by intravascular volume shifts and can produce severe hemodynamic deterioration
Vagal maneuvers Adenosine, which is the drug of choice Verapamil (2.5 to 10 mg given intravenously) terminates AV nodal
reentry successfully in about 90% of cases Amiodarone Esmolol Phenylephrine (100 µg by intravenous bolus) is administered if
the patient is hypotensive Intravenous digitalization is performed with one of the short-
acting digitalis preparations Synchronized cardioversion may be performed with incremental
doses of energy of 100, 200, 300, and 360 J,
Atrial Flutter
Atrial flutter does not always indicate severe heart disease. It can be seen in patients with CAD, mitral valve disease, pulmonary embolism, hyperthyroidism, cardiac trauma, cancer of the heart, and myocarditis.
Initial treatment should consist of control of the ventricular response rate with drugs that slow AV node conduction: β-Blockers such as esmolol (1 mg/kg by
intravenous bolus) or propranolol. Calcium channel blockers such as verapamil
(5 to 10 mg given intravenously) or diltiazem
If the ventricular response is excessively rapid or hemodynamic instability is present, or both, the following guidelines should be used:
Synchronized DC cardioversion starting at a relatively high energy of 100 J and gradually increasing to 360 J is indicated.
ibutilide (1 mg in 10 mL saline or 5% dextrose in water [D5W] infused slowly intravenously over a 10-minute period) has been documented to convert atrial flutter to sinus rhythm in most patients with relatively new-onset atrial flutter.[42] This may be repeated once, and although it is highly effective, life-threatening torsades de pointes may occur hours after ibutilide administration, thus making 4- to 8-hour monitoring after treatment highly desirable.
Procainamide (5 to 10 mg/kg for the intravenous loading dose, infused no faster than 0.5 mg/kg/min) may rarely be used in an attempt to restore sinus rhythm after the ventricular response has been adequately controlled.[43]
Amiodarone (150-mg intravenous loading dose infused over a 10-minute period, followed by 1 mg/min intravenously for 6 hours, a 0.5-mg/min intravenous infusion for 18 hours, and then a reduced intravenous dose or switching to an oral dose) has recently been shown to be effective.
Atrial Fibrillation
Atrial fibrillation is the most common postoperative arrhythmia and has significant consequences
Numerous studies support the efficacy of β-blockers in the prevention of postoperative atrial fibrillation. Perioperative administration of amiodarone, sotalol, nondihydropyridine calcium channel blockers, and magnesium sulfate has also been associated with a reduction in the occurrence of atrial fibrillation
Acute atrial fibrillation: Treatment of acute atrial fibrillation is very similar to that for atrial flutter. Primary attention should be focused on controlling the ventricular response, especially with the administration of diltiazem or esmolol intravenously
Junctional Rhythms
Junctional rhythms are common in patients under anesthesia (about 20%), especially with halogenated anesthetic agents. Junctional rhythms frequently decrease blood pressure and cardiac output by about 15%, but they can decrease it up to 30% in patients with heart disease
Usually, no treatment is required, and the rhythm reverts spontaneously. If hypotension and poor perfusion are associated with the rhythm, treatment is indicated. Atropine, ephedrine, or isoproterenol can be used in an effort to increase the activity of the SA node so that it will take over as the pacemaker.
Ventricular Premature Beats
VPBs are common during anesthesia, where they account for 15% of observed arrhythmias. They are much more common in anesthetized patients with preexisting cardiac disease.
VPBs result from ectopic pacemaker activity arising below the AV junction
The new onset of VPBs must be considered a potentially serious event because the arrhythmia may progress to VT or VF d/t coronary artery insufficiency, MI, digitalis toxicity with hypokalemia, and hypoxemia
In most patients, VPBs (occurring as single, bigeminy, or trigeminy but excluding nonsustained VT) do not need to be treated, particularly if the patient does not have an acute coronary syndrome, and treatment is generally dictated by the presence of symptoms attributable to the VPBs
First step in treatment is to correct any underlying abnormalities such as decreased serum potassium or low arterial oxygen tension.
If the arrhythmia is of hemodynamic significance or if it is believed to be a harbinger of worse arrhythmias, lidocaine is the treatment of choice, with an initial bolus dose of 1.5 mg/kg. Recurrent VPBs can be treated with a lidocaine infusion at 1 to 4 mg/min; additional therapy includes esmolol, propranolol, procainamide, quinidine, disopyramide, atropine, verapamil, or overdrive pacing.
Ventricular Tachycardia
The presence of three or more sequential VPBs defines VT
Acute onset is life threatening and requires immediate treatment.
If the patient is hemodynamically stable, amiodarone administered as one or more intravenous doses of 150 mg in 100 mL saline or D5W over a period of 10 minutes, followed by an intravenous infusion of 1 mg/min for 6 hours and 0.5 mg/min thereafter, is the recommended current treatment (maximum intravenous dose, 2.2 g/24 hr)
Lidocaine and procainamide have been used with varying degrees of success to treat VT
Synchronized cardioversion is the indicated nonpharmacologic intervention in any wide-complex tachycardia, whether monomorphic VT or a wide-complex SVT.
Polymorphic VT with a normal QT interval is treated with amiodarone and cardioversion
Polymorphic VT with a prolonged QT interval is a more serious rhythm disturbance, and the recommended current treatment is an intravenous infusion of 1 g of magnesium administered over a 2- to 3-minute period.
Ventricular Fibrillation
Ventricular fibrillation is an irregular rhythm that results from a rapid discharge of impulses from one or more ventricular foci or from multiple wandering reentrant circuits in the ventricles
There is no effective cardiac output, and life must be sustained by artificial means, such as external cardiac massage
Cardiopulmonary resuscitation must be initiated immediately, and then defibrillation must be performed as rapidly as possible.
Asynchronous external defibrillation should be performed with a DC defibrillator using incremental energies in the range of 200 to 360 J.
Early administration of 1 g of magnesium sulfate may facilitate defibrillation. In some instances, epinephrine has been used to facilitate defibrillation. Vasopressin has been added as a drug for the treatment of ventricular fibrillation
Supportive pharmacologic therapy may include lidocaine, amiodarone, bretylium, procainamide, phenytoin, or esmolol.
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