HEART BLOCKS AND CARDIAC PACEMAKERS

1. HEART BLOCKS AND CARDIAC PACEMAKERS Arun Abbi Jason Mitchell Jan 21, 2010

2. OUTLINE • SINUS NODE DYSFUNCTION • ATRIOVENTRICULAR BLOCKS • INTRODUCTION TO CARDIAC PACEMAKERS • INSERTION OF TRANSVENOUS CARDIAC PACEMAKER

3. HEART BLOCK • RELEVENT ANATOMY • Conduction: SA > Atrium > AV Node > His > Purkinje Network • AV node highly innervated • Responsive to sympathetic and vagal stimuli • RCA blood supply • His bundle less responsive • Dual blood supply

4. SINUS NODE DYSFUNCTION • Abnormal sinus impulse formation and propagation • AKA Sick Sinus Syndrome • Umbrella term for: • Sinus bradycardia • Sinus arrest • Sinoatrial exit block • Tachy-brady syndrome

5. SINUS NODE DYSFUNCTION • ETIOLOGY • Unclear • Fibrosis (most common) • Structural heart disease • Medications • Electrolyte imbalances (HypoK, HypoCa) • Endocrine (HypoTSH, HypoT)

6. SINUS NODE DYSFUNCTION • SINUS ARREST • Absent sinus P waves > 2 – 3 seconds • Result of absent sinus impulse formation • Duration of pause is not a function of the P-P interval

7. SINUS NODE DYSFUNCTION • SINOATRIAL EXIT BLOCK • Conduction delay between sinus node and atrium • Three types

8. SINUS NODE DYSFUNCTION • SINOATRIAL EXIT BLOCK • First Degree • Conduction delay between sinus node and atria • Cannot be identified on ECG • ?Clinical significance

9. SINUS NODE DYSFUNCTION • SINOATRIAL EXIT BLOCK • Second Degree • Intermittant conduction block • Type I (Wenkebach) – Progressive shortening of P-P intervals – Pause duration less than twice the P interval – Grouped P waves

10. SINUS NODE DYSFUNCTION • SINOATRIAL EXIT BLOCK • Type II – Pause duration that is a multiple of the P-P interval

11. SINUS NODE DYSFUNCTION • SINOATRIAL EXIT BLOCK • Third Degree • Complete conduction block from sinus node to atrium • Cannot be distinguished from sinus arrest on ECG • Typically results in an escape rhythm

12. SINUS NODE DYSFUNCTION • TACHY-BRADY SYNDROME • Bradycardia alternating with brief episodes of SVT • Usually Afib • ???Cause

13. ATRIOVENTRICULAR BLOCK • ETIOLOGY • Congenital • Acquired – Extensive DDX • Medications • Hyperkalemia (>6.3 mEq/L) • Hypoxia • Increased vagal tone • Ischemia/Infarction (~40%) • Fibrosis (~50%) • Infection/Inflammation • Vascular Disease • Idiopathic • Usually never identified

14. ATRIOVENTRICULAR BLOCK • FIRST DEGREE AV BLOCK • Prolongation of PR > 200 ms • Location of block • AV node, His bundle, His-Purkinje system • Correlate with QRS complex • Prognosis • Framingham: More likely to develop Afib, require permanent pacemaker, and increased all-cause mortality • Locate source of block • If AV node, generally benign and no further Ix • If infranodal, may require His-bundle electrocardiogram • No specific intervention required for stable 1st degree block

15. ATRIOVENTRICULAR BLOCK • FIRST DEGREE AV BLOCK

16. ATRIOVENTRICULAR BLOCK • SECOND DEGREE AV BLOCK • Type I (Wenckebach/Mobitz I) - Normal • Gradual prolongation of the PR interval followed by dropped QRS • Atrial impulses reach AV node while it is partially refractory • Location usually the AV node

17. ATRIOVENTRICULAR BLOCK • SECOND DEGREE AV BLOCK • Type II – Never normal • PR interval constant • Usually a result of underlying structural disease • Location typically His-Purkinje system • High Grade Second Degree • 2 or more consecutively blocked P waves

18. ATRIOVENTRICULAR BLOCK • SECOND DEGREE BLOCK • Different sites of involvement/prognoses • Type I: Generally involves AV node and is benign • Type II: Almost always infranodal and may progress to 3rd degree (slow unreliable escape) • Difficult to distinguish type in 2:1 conduction block

19. ATRIOVENTRICULAR BLOCK • THIRD DEGREE BLOCK • Complete AV node failure to conduct • Block may be anywhere in conduction system • Constant P-P and R-R intervals but no relationship • Variable PR intervals, Atrial HR > Ventricular HR • May be hemodynamically unstable • Slow heart rate may produce Torsade , especially in women

20. HEART BLOCK • ECG PRACTICE

21. ECG 1

22. SSS (Tachy-Brady)

23. ECG 2

24. Type II Second Degree AV Block

25. ECG 3

26. Sinus Arrest

27. ECG 4

28. 3rd Degree AV Block

29. ECG 5

30. Type II Second Degree SA Node Exit Block

31. ECG 6

32. First Degree AV Block

33. ECG 7

34. Type 1 Second Degree AV Block

35. HEART BLOCK • INITIAL ASSESSMENT • Hemodynamic Instability • Fatigue, Dizziness, NV, Diaphoresis • Hypotension • Syncope • Dyspnea • Chest Pain • ACLS Guidelines for Symptomatic Bradycardia • Medications • Β- Blockers • Ca2+ Channel Blockers • Digitalis • Amiodarone

36. HEART BLOCK • INITIAL ASSESSMENT • Investigations • Stabilize first! • ECG • Bloodwork • Electrolytes • Dig level • Troponin

37. HEART BLOCK • MANAGEMENT • O2, IV, Monitors • Transcutaneous pacing • Transvenous pacing • > 30 minutes transcutaneous pacing • Unable to obtain capture • Consider atropine • Consider catecholamines (be cautious)

38. HEART BLOCK • CARDIOLOGY CONSULTATION • Outpatient • New, asymptomatic Type I 2nd Degree (while awake) • Inpatient • Any symptomatic block • New, asymptomatic Type II 2nd Degree • Asymptomatic 3rd Degree • Concomitant MI/Ischemic symptoms • High Grade AV Block

39. CARDIAC PACING • INDICATIONS • Temporary • Any symptomatic AV block • Asymptomatic, but associated with Torsade • Permanent • ACC/AHA/HRS 2008 Guidelines: • Divided into Class Based Recommendations

40. CARDIAC PACING

41. CARDIAC PACING • INDICATIONS AV Block • Class I • 2nd and 3rd Degree • Bradycardia with symptoms (C) • Associated arrhythmias and medications that produce symptomatic bradycardia (C) • Asymptomatic, but asystole >3 sec or escape < 40 bpm or wide QRS escape or Afib and bradycardia with systole >5 seconds (C) • After ablation of AV node or unresolving post-op block (C) • Associated with MD, Kearns-Sayre syndrome, Erb dystrophy (B) • Associated with exercise w/o MI (B)

42. CARDIAC PACING • INDICATIONS AV Block • Class IIa • Asymptomatic persistent 3rd degree with escape > 40 (C) • Asymptomatic 2nd degree with intra or infra-Hisian block (B) • Symptomatic 1st or 2nd degree block (B) • Asymptomatic 2nd degree block with narrow QRS (B) • Class IIb • 1st or 2nd degree with MD, Erb dystrophy, peroneal muscular atrophy +/- symptoms (B) • AV block in setting of drug toxicity when block expected to recur (B)

43. CARDIAC PACING • INDICATIONS AV Block • Class III • Not indicated for asymptomatic 1st Degree (B) • Not indicated for asymptomatic Mobitz I with block at AV node (C) • Not indicated for AV block that is expected to resolve and unlikely to recur (drug toxicity, Lyme disease, transient increased vagal tone) (B) • Also not indicated in: • PEA Arrest • Traumatic cardiac arrest

44. Some Things Just Won’t Work

45. CARDIAC PACING • PACING MODES • 5 Position Nomenclature • First 3 Positions most common in pacemaker description • Position I: Chamber being paced • Atrium (A), Ventricle (V), Both (D), None (O) • Position II: Chamber being sensed • Atrium (A), Ventricle (V), Both (D), None (O) • Position III: Pacemaker’s response to sensing • Triggers (T), Inhibits (I), Both (D), None (O)

46. CARDIAC PACING • PACING MODES • Position IV: Programmability and Rate Control • Hierarchical • Rate Modulation (R), Communicating (C), Programmable (P), (O) • Position V: Antitachydysrrhythmia Function • Pacing (P), Shocking (S), Both (D)

47. CARDIAC PACING • PACING MODES • Most pacemakers encountered are: • AAIR – Useful for sinus node dysfunction with intact AV node • VVIR – Useful for chronically ineffective atria (AF, AFlutter) • DDD – Most common. Preserves AV synchrony • Reduces risk of AF, reduces signs/symptoms HF, improves QOL • No significant mortality benefit over single-chamber pacing

48. CARDIAC PACING • ECG MANIFESTATIONS • Depends on Pacing Mode • Atrial Pacing • Small pacemaker spike prior to P wave with normal morphology • Ventricular Pacing • LBBB-like and prolonged, inverted QRS (V5/6) and LAD

49. CARDIAC PACING

50. CARDIAC PACING