cardiology

1. Heart blocks and Pacemakers
2019
DR Ihab Suliman
MBBS ECFMG MRCP(UK) ABcv MRCP spec (End
and DM) CBNC FESC
Abstract committee grader for ESC Conference
2019

3. First Degree AVB
• Conduction delay can occur in:
• Atrium: 3% of cases
– May be due to intratrial pathology
– EKG findings: widening of P wave and decreased P wave voltage
• AV node:
– Most common site
– Common causes: increased vagal tone, CCB, digoxin, BB
– EKG findings: long PR interval with a narrow or wide P wave and
narrow QRS
• Bundle of His:
– Drugs that block sodium channels can impair depolarization and slow
conduction (Quinidine, procainamide)

4. First Degree AVB
• Clinical significance – none
• Treatment – none
• May progress to 2nd or 3rd degree AVB

5. Second Degree AVB
• Some atrial impulses fail to reach the
ventricles
• 2 types:
– Mobitz Type I (Wenckebach): progressive PR
interval lengthening to a non-conducted P wave
– Mobitz Type II: PR interval constant prior to P
wave that does not conduct to the ventricles.

6. SECOND DEGREE A-V BLOCK
(MOBITZ I OR WENCKEBACH)

7. Mobitz Type I (Wenckebach) AVB
• Most often involves AV node
• Benign
• Features:
– Gradually increasing PR interval
– Gradually decreasing R-R interval
– Dropped beat
– Largest delay occurs in the first beat and then decreases
beat to beat until block occurs and cycle is reset
– Group beating: 3:2,4:3 etc.

8. Second Degree Heart Block (2º)
Mobitz Type I
(Wenkebach)
PR PR PR DROPPED BEAT

9. Mobitz Type I
• Clinical implications:
– Often asymptomatic
– May have some symptoms eg lethargy, confusion
– If cardiac output is reduced, patient may
experience angina, syncope or heart failure due to
bradycardia and resultant hypoperfusion state.
– Can occur in athletes with high vagal tone
– Elderly: aging prolongs cycle length

10. Further implications:
• Underlying IHD:
– Mobitz type I can be complication of inferior MI as:
– RCA supplies inferior and posterior walls and AV and SA
nodes
– Associated with increased mortality
• Treatment:
– Removing reversible causes (ischemia, increased vagal
tone, medications
– Pacemaker if symptomatic during day
– No pacemaker is symptoms at night
• May progress to 3rd degree AVB

11. MOBITZ TYPE II

12. Mobitz Type II AVB
• Always occurs below the AV node
– 20% within Bundle of His
– 80% in bundle branches
• Widened QRS
• PR interval may be normal or slightly prolonged but
constant
• Non-conducted P wave on EKG
• Clinical implications:
– Dizziness
– Presyncope
– Syncope

13. Mobitz Type II AVB
• Type II is permanent and may progress to
higher levels of block
• Treatment:
– Remove reversible causes
– Potential candidates for pacemaker insertion

14. Second Degree AVB 2:1
• Unable to classify as Mobitz type I or II
• Ratio of 2 P waves to 1 QRS
• Clinical significance:
– Will be associated with symptoms (dizziness,
lethargy etc.)
– May progress to 3rd degree AVB
• Treatment - pacemaker

15. THIRD DEGREE A-V BLOCK

16. Third degree (complete) AVB
• No atrial impulses reach the ventricles due failure of
AV node therefore no P wave conduction
• AV dissociation (Ps marching through…)
• QRS complex:
– Narrow: block at AV node to level of bundle of His
– Wide: block below level of bundle of His
• More distal the block the slower the escape rhythm
– If <40bpm: pacemaker is unreliable causing profound
bradycardia or asystole
– Syncope is very common

17. Clinical Significance
• Clinical Implications:
– Dizziness
– Presyncope
– Syncope
– Ventricular tachycardia
– Ventricular fibrillation
– Confusion
– Can worsen angina and CHF
• Treatment:
– Pacemaker!

18. Class I Indications for Permanent Pacing in
Adults per AHA/ACC
1. 3rd degree AVB at any anatomic level associated
with any of the following:
• Symptomatic bradycardia (secondary to AVB)
• Symptomatic bradycardia (secondary to drugs required
for management of dysrhythmias or other medical
conditions)
• Documented asystole >3s or escape rate of <40 bpm in
awake, asymptomatic patient
• After ablation of AV node
• Postoperative AVB that is not expected to resolve
• Neuromuscular disease with AVB (neuromuscular
dystrophies)

19. 2. Symptomatic bradycardia from 2nd degree AVB regardless of type or
site of block.
3. Chronic bifascicular or trifascicular block with intermittent 3rd
degree AV block or type II 2nd degree AVB.
4. After AMI with any of the following:
– Persistent 2nd degree AVB at the His-Purkinje level with
bilateral bundle branch block or 3rd degree AVB at or below
His-Purkinje system
– Transient 2nd or 3rd degree infranodal AVB and associated BBB
– Symptomatic, persistent 2nd or 3rd degree AVB
5. Sinus node dysfunction with symptomatic bradycardia or
chronotropic incompetence.
6. Recurrent syncope caused by carotid sinus stimulation.

20. Pacemaker indications: Class IIa
• Complete AVB without symptoms:
– >40bpm while awake = Class IIa indication
– UNLESS:
• Activity or exercise is limited
• Heart begins to enlarge
• LV function is depressed
• LA enlargement is noted
• Intra- or infra-Hisian block issuspected with of without QRS
widening
• QT interval prolongation
• Ventricular arrhythmias
• Episodic profound bradycardia (during sleep or awake)

21. Pacemaker indications: take home points!
• Complete AVB with:
– Associated symptoms
– Ventricular pauses >3s
– Resting HR <40 bpm while awake
= pacemaker!

22. LBBB in NSR

23. RBBB

24. A Brief History of Pacemakers

25. Just kidding…but did you know?
• The implantable cardiac pacemaker was
discovered by mistake!
• Wilson Greatbatch was building an oscillator to
record heart sounds. When he accidentally
installed a resistor with the wrong resistance into
the unit, it began to give off a steady electrical
pulse. Greatbatch realized that the small device
could be used to regulate the human heart.
• After two years of refinements, he had hand-
crafted the world's first successful implantable
pacemaker (patent #3,057,356). Until that time,
the apparatus used to regulate heartbeat was the
size of a television set, and painful to use.
• Greatbatch later went one step further, inventing
a corrosion-free lithium battery to power the
pacemaker. All told, his pacemakers and batteries.
• Thus in 1985 the National Society of Professional
Engineers named Greatbatch's invention one of
the ten greatest engineering contributions to
society of the last 50 years.

26. Pacemaker Functions
1. Stimulate cardiac depolarization
2. Sense intrinsic cardiac function
3. Respond to increased metabolic demand by
providing rate responsive pacing
4. Provide diagnostic information stored by the
pacemaker

27. • Pulse generator: power
source or battery
• Leads or wires
• Cathode (negative
electrode)
• Anode (positive
electrode)
• Apex of right ventricle
IPG
Lead
Anode
Cathode
Pacemaker Components Combine with Body
Tissue to Form a Complete Circuit