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 Inpatient
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 Permanent
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 Class IIb
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 Also not indicated in:
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
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

51. CARDIAC PACING TEMPORARY PACING
Goal: Restore effective myocardial contraction to increase adequate cardiac output
Transcutaneous vs. transvenous pacing modalities

52. CARDIAC PACING TRANSCUTANEOUS PACING
Temporary stabilization of symptomatic bradycardia
Most patients tolerate pacing for < 15 minutes
Pain directly related to current and inversely related to pad size

53. CARDIAC PACING TRANSCUTANEOUS PACING Technique
Apply pads front/back or left/right
Front/back preferred
Sedate
Set HR to 60-80
Set current to 0 mA
Choose mode
Synchronous vs. asynchronous
Turn pacemaker on
Increase current by 10 mA increments until capture obtained
Manifested by wide QRS relating to palpable carotid pulse
If unconscious, start at 200 mA and decrease to lowest current

54. CARDIAC PACING TRANSVENOUS PACING
Placement of electrode into R Ventricle
Pacer is VVI mode
Allows for asynchronous vs synchronous

55. CARDIAC PACING TRANSVENOUS PACING Equipment Introducer Kit
Introducer sheath
Pacing catheter
External pacing generator
Cardiac monitor

56. CARDIAC PACING TRANSVENOUS PACING External Pacing Generator
Delivers electrical current (mA)
Output Control Dial
Regulates current from 0.1 – 20 mA
Rate Control Dial
Selects pacing rate
Sensitivity Control Rate
Threshold suppression of pacer based on native R wave
Asynchronous pacing when sensitivity control turned down

57. CARDIAC PACING TRANSVENOUS PACING Transvenous Pacing Catheter
3 types:
Flexible, Semifloating, Rigid/Non-floating
Risk of cardiac perforation with rigid catheters
Two electrodes attached: + and –
Introducer Sheath
Facilitates central venous access

58. CARDIAC PACING TRANSVENOUS PACING Technique
Seldinger technique for central venous access
R IJ or L Subclavian shown to be most successful
Secure introducer sheath
Introduce pacing electrode
Inflate balloon when electrode passed through the 20 cm mark
Moot if no pulse
Set pacing generator to max current
Set rate between 60-80
Asynchronous sensitivity

59. CARDIAC PACING TRANSVENOUS PACING
As cath is advanced, monitor will show pacing spikes
Pacing spikes followed by wide QRS indicating of RV placement
Electrical capture
Assess for pulse
Mechanical capture
Deflate balloon and secure cath in place
Set pacing threshold

60. CARDIAC PACING TRANSVENOUS PACING Complications
Inherent to central venous access
Arterial puncture, PTX, infection
Right heart catheterization
Failure to capture, failure to sense, dysrrhythmias
Cardiac perforation
Lead displacement
Electrode coiling