Arrhythmias

1. Arrhythmias

2. Definitions • Arrhythmias = abnormalities of the heart rate or the heart rhythm • Tachycardia is a HR >100 • Increased pacemaker activity: faster depolarization, lower thresholds, or oscillations during repolarization trigger early action potentials • Re-entry circuits: depolarization travels in a circle…if tissue is not refractory when the impulse returns, it will depolarize again producing a recurring circuit • Bradycardia • HR <60 • Due to abnormal and/or delayed conduction

3. General Management • Prevention • Early correction of • Hypoxemia • Electrolyte imbalances • Acid-base imbalances • Cardiac ischemia • Arrhythmogenic factors • Pain • Vagal stimulation • Drugs • Cardiac irritants

4. General Management, cont… • Tachyarrhythmias • Detrimental when they cause symptoms or reduce tissue perfusion • Must be terminated immediately if they cause hypotension, pulmonary edema, or angina • Bradyarrhythmias • Treated with atropine, beta agonists, or pacemaker if symptomatic • Not all will require treatment…if the person is stable and asymptomatic you can treat the cause without converting the rhythm

5. General Management, cont… • Vagal stimulation • Carotid sinus massage • Slows HR and may cardiovert some SVT’s • Antiarrhythmic drugs • Selected according to the rhythm and the underlying pathophysiology • Therapeutic windows are often narrow • Side effects are common • Therapy is frequently ineffective • They may cause other arrhythmias • Arrhythmia suppression does not always improve outcomes

6. General Management, cont… • Non-pharmacologic therapies • DC cardioversion • Uses 50-360 joule shocks • Timed to deliver on the QRS • Defibrillation • Uses 50-360 joule shocks • Not timed • May be external or implanted • Radiofrequency catheter ablation (RFCA) • Heat is delivered through a catheter to a specific site in the heart

8. Diagnosis • Not always easy because artifact can interfere with the EKG tracings • Narrow QRS complex tachycardias • Usually due to SVT • Can be terminated with IV adenosine • Wide QRS complex tachycardias • Usually due to V tach, but could also be SVT with abnormal conduction • Treat as if it were VT (cardioversion/lidocaine)…if no response, then try adenosine

9. Tachyarrhythmias • Supraventricular tachycardias • Orginate above the AV node • Present with dizziness, palpitations, dyspnea • Are not usually life-threatening • Types • Sinus tachycardia • a normal response to stress, exercise, hypoxemia, fever, increased sympathetic tone • Treat by removing the cause • Atrial tachycardia: • due to ectopic atrial automaticity in chronic heart/lung dx • associated with metabolic, acid-base, or drug toxicity • Treat by correcting the underlying metabolic defect or with RFCA

11. Tachyarrhythmias, cont… • Atrial flutter • A re-entry tachycardia involving the whole atrium • Atrial rate is ~300/min • Ventricular rate depends on AV conduction • Treated with digoxin • Atrial fibrillation • Multiple re-entry circuits with chaotic atrial rhythm • Atrial rate is ~500/min • Ventricular rate depends on AV condution…considered controlled as long as ventricular rate <100 • Stasis of blood from ineffective contraction predisposes to thrombus formation • Treat with digoxin, anticoagulants, cardioversion • Re-entry tachycardia • Re-entry circuits via many AV node conduction pathways • Responds to vagal stimulation and drugs that slow AV conduction, such as adenosine

13. Tachyarrhythmias, cont… • Ventricular tachycardias • Arise in the ventricles of patients with heart dx, cardiomyopathy, or congential heart dx • Generally more serious than atrial tachs • Types • Ventricular tachycardia • Usually caused by re-entry circuits that form with scarring but can be ectopic automaticity • Usually causes hemodynamic decompensation • Ventricular rate ~150-250 • Treat with cardioversion or drugs to suppress the rhythm

15. Tachyarrhythmias, cont… • Ventricular fibrillation • Chaotic ventricular rhythm that frequently follows an acute MI • Immediate loss of CO with unconsciousness • Treat with defibrillation…the sooner the better • May use drugs to prevent recurrence or implantable defibrillator

16. Bradyarrhythmias • Well tolerated by normal hearts, but CO and BP will fall if SV can’t increase • Types • Sinus bradycardia • Normal EKG with rate <60 • Causes: • vagal reflexes (pain, hypoxemia) • Drug toxicity (beta blockers, digoxin) • AV node ischemia • Treatment: • Atropine • Beta agonists • Drug antidotes

18. Bradyarrhythmias, cont… • Heart block • Usually due to ischemic damage to nodal or conducting tissue • Common after an inferior MI b/c right coronary artery supplies the AV node in most people • Presence after an anterior MI suggests a large infarction • First degree • slow AV conduction…PR interval exceeds 0.2 seconds • Usually benign • Second degree • Some atrial beats are not conducted to the ventricles

19. Bradyarrhythmias, cont… • Types of second degree heart block • Mobitz I (Wenckebach) • Causes PR interval to lengthen with each beat, culminating in the failure of an atrial impulse to be transmitted to the ventricle (dropped beat) • Sequence is repetitive • Treatment is usually not needed • Mobitz II • Originates below the AV node in the bundle of HIS or Purkinje fibers • Every 2nd or 3rd atrial impulse initiates a ventricular contraction…the others are blocked • May require pacemaker insertion

21. Bradyarrhythmias, cont… • Third degree heart block (complete heart block) • Conduction between the atria and ventricles ceases • The atria contract at one rate…the ventricles contract at another rate (usually 20-40) • Requires pacemaker insertion