Cardiac Arrhythmias II : Tachyarrhythmias

1. Cardiac Arrhythmias II: Tachyarrhythmias Michael H. Lehmann, M.D. Clinical Professor of Internal Medicine Director, Electrocardiography Laboratory

2. Supraventricular Tachycardias (Supraventricular - a rhythm process in which the ventricles are activated from the atria or AV node/His bundle region)

3. Supraventricular Tachycardia (SVT) Terminology • QRS typically narrow (in absence of bundle branch block); thus, also termed narrow QRS tachycardia • Usually paroxysmal, i.e,starting and stopping abruptly; in which case, called PSVT • “Paroxysmal Atrial Tachycardia (PAT)” - the older term for PSVT - is misleading and should be abandoned

4. AV Junctional Reentrant Tachycardias (typically incorporate AV nodal tissue)

5. Mechanism of Reentry Bidirectional Conduction Unidirectional Block Recovery of Excitability & Reentry

6. AV Nodal Reentrant Tachycardia

7. AV Nodal Reentrant Tachycardia Circuit F = fastAV nodal pathway S = slow AV nodal pathway (His Bundle) During sinus rhythm, impulses conduct preferentially via the fast pathway

8. Initiation of AV Nodal Reentrant Tachycardia PAC PAC PAC = premature atrial complex (beat)

9. Sustainment of AV Nodal Reentrant Tachycardia Rate 150-250 beats per min P waves generated retrogradely (AV node  atria) and fall within or at tail of QRS

10. Sustained AV Nodal Reentrant Tachycardia V1 P P P P Note fixed, short RP interval mimicking r’ deflection of QRS

11. Orthodromic AV Reentrant Tachycardia Anterogade conduction via normal pathway AP Retrograde conduction via accessory pathway (AP)

12. Initiation of Orthodromic AV ReentrantTachycardia PAC Atria AP AVN Ventricles PAC = premature atrial complex (beat)

13. Sustainment of Orthodromic AV Reciprocating Tachycardia Atria Rate 150-250 beats per min AP AVN Ventricles Retrograde P’s fall in the ST segment with fixed, short RP

14. Accessory Pathway with Ventricular Preexcitation (Wolff-Parkinson-White Syndrome) Sinus beat Hybrid QRS shape “Delta” Wave PR < .12 s AP Fusion activation of the ventricles QRS  .12 s

15. Varying Degrees of Ventricular Preexcitation

17. Intermittent Accessory Pathway Conduction V Preex V Preex Normal Conduction Note “all-or-none” nature of AP conduction

18. Orthodromic AV Reentrant Tachycardia NSR with V Preex Note retrograde P waves in the ST segment SVT: V Preex gone

19. Concealed Accessory Pathway Sinus beat No Delta wave during NSR (but AP capable of retrograde conduction)

20. Summary of AV Junctional Reentrant Tachycardias • Reentrant circuit incorporates AV nodal tissue • P waves generated retrogradely over a fast pathway • Short, fixed RP interval

21. Clinical Significance of AV Junctional Reentrant Tachycardias • Rarely life-threatening • However, may produce serious symptoms (dizziness or syncope [fainting]) • Can be very disruptive to quality of life • Involvement of an accessory pathway can carry extra risks

22. Atrial Tachyarrhythmias

23. Sinus Tachycardia (100 to 180+ beats/min) • P waves oriented normally • PR usually shorter than at rest

24. Causes of Sinus Tachycardia • Hypovolemia ( blood loss, dehydration) • Fever • Respiratory distress • Heart failure • Hyperthyroidism • Certain drugs (e.g., bronchodilators) • Physiologic states (exercise, excitement, etc)

25. Premature Atrial Complex (PAC) V5 Non-Compensatory Pause P P P P’ P Timing of Expected P

26. Premature Atrial Complex (PAC): Alternative Terminology • Premature atrial contraction • Atrial extrasystole • Atrial premature beat • Atrial ectopic beat • Atrial prematuredepolarization

27. PACs: Bigeminal Pattern P P’ P P’ P P’ • Note deformation of T wave by the PAC • “RegularlyIrregular” Rhythm

28. PACs with Conduction Delay/Block Physiologic AV Block P P’ Physiologic AV Delay P P’ Recovered AV Conduction P P’

29. PAC with “Aberrant Conduction” (Physiologic Delay in the His Purkinje System) V1 P P P’ P RBBB

30. PACs with Aberrant Conduction (Physiologic RBBB and LBBB) V1 Normal conduction LBBB RBBB

31. PACs with Physiologic LBBB and His-Purkinje System Block V1 Non-conducted PAC

32. Non-Conducted PAC V5 V1 P P P’ P Note deformation of T wave by the PAC

33. Bigeminal/Blocked PACs Mimicking Sinus Bradycardia V1 Only the 4th bigeminal PAC conducts

34. Clinical Significance PAC’s • Common in the general population • May be associated with heart disease • Can be a precursor to atrial tachyarrhythmias

35. Atrial Tachycardia V1 • RP intervals can be variable • RP often > PR • (Example slower than more common rate mof 150-250 beats per min) Differs from AV nodal or AV reentrant SVT

36. Clinical Significance of Atrial Tachycardia • Similar to sequela of AV junctional reentrant tachycardias • Must be differentiated from them diagnostically

37. Atrial Flutter (“Typical,” Counterclockwise) Reentrant mechanism

38. Atrial Flutter Classic inverted “sawtooth” flutter waves at 300 min-1 (best seen in II, III and AVF) II 2:1 4:1 V1 Note variable ventricular response

39. Atrial Flutter V. rate 140-160 beats/min 2:1 Conduction (common) 2:1 & 3:2 Conduction 1:1 Conduction (rare but dangerous)

40. Atrial Fibrillation Focal firing or multiple wavelets Chaotic, rapid atrial rate at 400-600 beats per min

41. Atrial Fibrillation V5 V1 • Rapid, undulating baseline(best seen in V1) • Most impulses block in AV node Erratic conduction

42. Atrial Fibrillation: Characteristic “Irregularly Irregular” Ventricular Response II

43. Atrial Fibrillation with Rapid Ventricular Response II Irregularity may be subtle

44. Atrial Fibrillation: Autonomic Modulation of Ventricular Response Baseline Immediately after exercise

45. Clinical Significance of Atrial Flutter and Fibrillation • Causes • Usually occur in setting of heart disease; but sometimes see “lone “ atrial fibrillation • Hyperthyroidism (atrial fibrillation) • May acutely precipitate myocardial ischemia or heart failure • Chronic uncontolled rates may induce cardiomyopathy and heart failure • Both can predispose to thromboembolic stroke, etc

46. Varying Degrees of Ventricular Preexcitation

47. Atrial Fibrillation with Rapid Conduction Via Accessory Pathway

48. Atrial Fibrillation with Third Degree AV Block V1 V5 Regular ventricular rate reflects dissociated slow junctional escape rhythm

49. Regular Narrow QRS Tachycardias

50. Differential Diagnosis of Regular Narrow QRS (Supraventricular) Tachycardia • Reentrant SVT incorporating AV nodal tissue • AV nodal reentrant tachycardia • Orthodromic AV reentrant tachycardia • SVT mechanism confined to the atria • Sinus tachycardia • Atrial flutter • Other regular atrial tachycardias • Short-RP favors AV node-dependent reentrant SVT