Heart block

Heart block
Dr Praveen Gupta
05.12.2017
JIPMER
Pondicherry
India
CLT students class
1

Atrioventricular block (heart block)
 An AV block exists if the atrial impulse is conducted with delay or is not conducted
at all to the ventricle when the AV junction is not physiologically refractory
 During AV block, block can occur in AV node, His bundle, or bundle branches
 Disturbance of impulse conduction that can be permanent or transient
2Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 10th Edition, Chpater 37, Page no 792-95

Classified by severity into three categories
 First-degree heart block, conduction is prolonged but all impulses are conducted
 Second-degree heart block in two forms, Mobitz type I (Wenckebach) and type II
 Type I heart block is characterized by progressive lengthening of the conduction
time until an impulse is not conducted
 Type II heart block denotes an occasional or repetitive sudden block of conduction
of an impulse, without prior measurable lengthening of conduction time.
 When no impulses are conducted, complete or third-degree block
 Advanced or highgrade heart block,indicate blockage of two or more consecutive
impulses

First-Degree Atrioventricular Block
 Every atrial impulse is conducted to the ventricles and a regular ventricular rate
 PR interval exceeds 0.20 second in adults.
 PR intervals can exceed the P-P interval, known as skipped P waves
 Result from a conduction delay in the AV node (A-H interval), in the His-Purkinje
system (H-V interval), or at both sites
 Equally delayed conduction over both bundle branches
 Intra-atrial conduction delay can result in PR prolongation

First-Degree Atrioventricular Block
 QRS complex on the scalar ECG is normal, the AV delay in the AV node
 QRS complex shows a bundle branch block pattern, the conduction delay within the AV node
or the His-Purkinje system
 Acceleration of the atrial rate or enhancement of vagal tone by carotid massage cause first-
degree AV nodal block to progress to type I second-degree AV block

Second-Degree Atrioventricular Block
 Blocking of some atrial impulses conducted to the ventricle
 Nonconducted P wave can be intermittent or frequent, occur at regular or irregular intervals,
and be preceded by fixed or lengthening PR intervals
 Type I second-degree AV block is characterized by progressive PR prolongation culminating
in a nonconducted P wave whereas in type II second-degree AV block, the PR interval
remains constant before the blocked P wave

3.2 AV block
7© 01/12/2017, Department of cardiology, JIPMER, Pondicherry, India

Second-Degree Atrioventricular Block
 AV block is intermittent and repetitive and can block several P waves in a row
 Mobitz type I and Mobitz type II are applied to the two types of block
 Wenckebach block refers to type I block only
 Type I conduction disturbance can be difficultm to recognize.
 During a typical type I block, the increment in conduction time is greatest in the second beat
of the Wenckebach group, and the absolute increase in conduction time decreases
progressively over subsequent beats.

2.1 AV block
9© 2017, Department of cardiology, JIPMER, Pondicherry, India

Characteristics of classic Wenckebach group beats
 Interval between successive beats progressively decreases, although conduction time
increases (but by a decreasing function)
 Duration of the pause produced by the nonconducted impulse is less than twice the interval
preceding the blocked impulse (which is usually the shortest interval)
 Cycle that follows nonconducted beat (beginning the Wenckebach group) is longer than cycle
preceding the blocked impulse
 Typical grouping occurs in < 50% of patients with a type I Wenckebach AV block

Differentiation of Type I from Type II
Atrioventricular Block
 A 2:1 AV block can be a form of type I or type II AV block
 If QRS is normal, block likely type I and in AV node, and search for transition of the 2:1
block to a 3:2 block, during which the PR interval lengthens in the second cardiac cycle
 If bundle branch block is present, block can be in AV node or His- Purkinje

Differentiation of Type I from Type II
Atrioventricular Block
 First-degree and type I second-degree AV block can occur in normal healthy children, and a
Wenckebach AV block normal in athletes due to increase in resting vagal tone
 In patients who have chronic second-degree AV nodal block (proximal to the His bundle)
without structural heart disease, the course is relatively benig, whereas in those with structural
heart disease, the prognosis is poor.

Third-Degree (Complete) Atrioventricular Block
 No atrial activity is conducted to the ventricles
 Atrial pacemaker can be sinus or ectopic (tachycardia, flutter, or fibrillation) or can
result from AV junctional focus above the block with retrograde atrial conduction
 Ventricular focus is located just below the region of the block, which can be above
or below the His bundle bifurcation.
 Ventricular pacemaker closer to the His bundle stable and faster escape rate than
can those located more distally in the conduction system.

Complete heart block
14© 01/12/2017, Department of cardiology, JIPMER, Pondicherry, India

 Result from a block at AV node, bundle of His, Purkinje
 If block proximal to the His bundle, there will be normal QRS complexes at 40 to
60 beats/minute
 Intrahisian block poor prognosis
 Acquired complete AV block occurs most commonly distal to the bundle of His
because of trifascicular conduction disturbance.
 QRS complex is abnormal, and ventricular rate < 40 beats/minute

 Paroxysmal AV block caused by vagotonic reflexes
 Surgery, electrolyte disturbances, myoendocarditis, tumors, Chagas disease,
rheumatoid nodules, calcific aortic stenosis, myxedema, polymyositis, infiltrative
processes (e.g., amyloidosis, sarcoidosis, scleroderma) can produce AV block
 Rapid rates sometimes followed by block (called tachycardia-dependent AV
block), which is thought to be due to a phase 3 block (block caused by incomplete
action potential recovery), postrepolarization refractoriness, and concealed
conduction in the AV node

 Pause-dependent paroxysmal AV block results in AV block after a pause or during
relative bradycardia
 Referred to as a phase 4 block because it is thought that spontaneous
depolarizations during the resting phase of the action potential result in an inability
to depolarize,

 In children AV block is congenital
 AV block can be an isolated finding or be associated with other lesions
 Neonatal autoimmune disease, account for most cases of heart block

 Children are asymptomatic, some children, symptoms requiring pacemake
 Adams-Stokes attacks can occur
 Heart rate at rest 50 beats/minute or less correlates with the incidence of syncope
 Prolonged recovery times of escape foci after rapid pacing , slow heart rates on 24-hour
electrocardiographic recordings, and the occurrence of paroxysmal tachycardias may be
factors predisposing to the development of symptoms

Clinical Features
 First-degree AV block, long a to c wave interval in the jugular venous pulse
 Diminished first heart sound
 In type I second-degree AV block, the heart rate may increase imperceptibly with gradually
diminishing intensity of the first heart sound; widening of the a to c interval, terminated by a
pause; and an a wave not followed by a v wave.
 Intermittent ventricular pauses and a waves in the neck not followed by v waves characterize
type II AV block. First heart sound maintains a constant intensity

Clinical Features
 In complete AV block, the findings are the same as those in AV dissociation
 Significant clinical manifestations of first- and second-degree AV block usually consist of
palpitations or subjective feelings of the heart “missing a beat.”
 Persistent 2:1 AV block can produce symptoms of chronic bradycardia
 Complete AV block can be accompanied by signs and symptoms of reduced cardiac output,
syncope or presyncope, angina, or palpitations from ventricular tachyarrhythmias

Management
 Holter or external loop recorders can be useful
 Longer periods of recording require an implantable loop recorder
 In patients with presyncope or syncope, one should suspect intermittent infra-His block in
those with bundle branch block or an intraventricular conduction defect.
 An EP study to thoroughly evaluate AV conduction (including infusion of isoproterenol
and/or procainamide) may be warranted to make the diagnosis, particularly in those with
severe symptoms

Management
 Drugs cannot be relied on to increase the heart rate
 Temporary or permanent pacemaker for symptomatic bradyarrhythmias.
 For short-term therapy, atropine are useful
 Isoproterenol can be used transiently
 Symptomatic AV block or high-grade AV block (e.g., infrahisian, type II AV block, third-
degree heart block not caused by congenital AV block), permanent pacemaker placement is
the treatment of choice.

Heart block

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