Class III: potassium Channel Blockers (drugs that delay repol) Delay repol of fast potentials Prolong both the action potential duration and the effective refractory period Class IV: calcium channel blockers Calcium channel blockade has the same impact on cardiac action potentials as does beta blockade, so these agents have nearly identical effects on cardiac function o SA node—reduce automaticity o AV node—slow conduction velocity o Atria and vent—reduce contractility Verapamil and diltiazem are employed as antidys Benefits derive from suppressing AV nodal conduction Other antidysrhythmic drugs Adenosine and digoxin don’t fit classes but suppress dysrhythmias by decreasing conduction thru the AV node and reducing automaticity in the SA node Common dysrhythmias and their trm Supraventricular dysrhythmias 25
Atrial dysrhythmias can have life-threatening effects on ventricular function Arise in areas of the heart above the ventricles Not specifically harmful cause does not significantly reduce cardiac output Supravent tachy can be dangerous o If atria drive cent at an excessive rate diastolic filling will be incomplete and cardiac output declines o Trm is slowing the cent rate (by blocking impulse conduction thru AV node) Acute trm is accomplished with o vagotonic maneuvers, DC cardioversion and certain drugs : class II, IV, adenosine and digoxin A fib o Caused by multiple atrial ectopic focus firing randomly o Produces irregular atrial rhythm o Depending on extent of impulse transmission thru AV vent rate may be rapid or normal o Carried high risk for stroke (blood trapped in atria) To prevent stroke pt are treated wit warfarin or newer anticoagulants For trm to restore normal sinus rhythm warfarin should be taken for 3 weeks pre op and 4 weeks post op For pt taking long term trm warfarin must be taken long term o Trm has two goals Restoring normal sinus rhythm DC cardioversion. Short term drug trm with amiodarone, sotalol or RF ablation Slowing vent rate (preferred) By long term therapy with beta blocker (atenolol or metoprolol) or cardio selective calcium channel blocker diltizam or verapamil Atrial Flutter o Caused by an ectopic focus discharging at 250-350 times per minute o One atrial impulse reaches the vent out of two TRM is choice of DC cardioversion o Pt may need to continue long term therapy with class IC or class III (antidysrhythmic drugs) to prevent recurrence o Need to take warfarin 3-4 wk before procedure and sev wk after IV ibutilide, Alternatives to cardioversion RF ablation Control of vent rate with drugs (verapamil, diltiazem, beta blocker o Risk of stroke Trm with anticoagulants Sustained supraventricular tachycardia (SVT) 26
o Caused by an AV nodal reentrant circuit o HR increased to 150-250 bpm o Responds to interventions that increase vagal tone Carotid massage or the Valsalva maneuver IV beta blocker or calcium channel blocker second resort or once dysrhythmia controlled Last resort amiodarone for prevention
You've reached the end of your free preview.
Want to read all 99 pages?
- Spring '14