Sick sinus syndrome describes dysfunction of the heart's sinoatrial node, which can cause abnormal heart rhythms like bradycardia (slow heart rate) and tachycardia (fast heart rate). It is usually seen in older adults and may be caused by non-specific degeneration of the heart's conduction system or conditions like amyloidosis. Symptoms include alternating slow and fast heart rhythms. Heart blocks occur when electrical signals are impaired moving through the heart, and are classified based on the level of impairment from first to third degree blocks.

2. SICK SINUS SYNDROME
Ahsan Sajjad
RMU-43

3. DEFINITION
• Sick sinus syndrome describes
dysfunction of the intrinsic
pacemaker of heart, the
sinoatrial node. As a result, the
cardiac rhythm becomes
abnormal characterized by:
 Sinus bradycardia…slow
heart rate
 Tachycardia…fast heart rate
 Bradycardia-
tachycardia…alternating slow
and fast heart rhythms.

4. MECHANISM
 Normally, the sinuatrial node produces a steady pace of regular
electrical impulses. In sick sinus syndrome, these signals are
abnormally paced. A person with sick sinus syndrome may have
heart rhythm that are too fast, too slow, punctuated by long pause
or an alternating combination of all of these rhythm problems.
 TYPES AND CAUSES
Types of sick sinus syndrome and their causes include:
SINUS BLOCK:
Electrical signals move too slowly through sinus node, causing
abnormally slow heart rate.
SINUS ARREST:
The sinus node activity pauses.
TACHYCARDIA-BRADYCARDIA SYNDROME:
The heart rate alternates between abnormally fast and slow
rhythms, often with a long pause (asystole) between heart beats.

5.  It may be brought on by use of drugs like digitalis, calcium channel
blockers, beta blockers and antiarrhythmics.
 Sick sinus syndrome usually occurs in people older than 50,in whom the
cause is often a non specific, scar like degeneration of the heart’s
conduction system like amyloidosis,sarcoidosis,chagas disease and
cardiomyopathies.
• In children, a common cause of sick sinus syndrome is heart
surgery especially on heart chambers.
• In coronary artery disease, high blood pressure, aortic and
mitral valve diseases may be associated with sick sinus
syndrome.

6. HEART BLOCKS
 Interference with the conduction process of the heart causes the
phenomena called heart block or atrioventricular block.
• Heart block is classified according to the level of impairment:
 First Degree Heart Block
 Second Degree Heart Block
 Third Degree (complete) Heart Block
FIRST DEGREE HEART BLOCK:
 First degree heart block or first degree atrioventricular block is
defined as prolongation of the PR interval on the ECG to more than
200msec.First degree heart block is considered “marked” when the
PR exceeds 300msec.While the conduction is slowed, there are no
missed beats.

7. MECHANISM
 With first degree atrioventricular (AV) block every atrial impulse is
transmitted to the ventricles ,resulting in regular ventricular rate.
This type of AV block can arise from delays in the conduction
system in the AV node itself, the His Purkinjie system or a
combination of both. Overall, dysfunction at the AV node is much
more common than dysfunction at the His Purkinjie system.
 If the QRS complex is of normal width and morphology on the ECG
than the conduction delay is almost always at the level of the AV
node.
 If however, the QRS demonstrates a bundle branch morphology
than the level of the conduction delay is often localized to His
Purkinjie system

8. CAUSES
 Following are the most common causes of first degree
(atrioventricular block).
 Intrinsic AV nodal disease.
 Enhanced vagal tone.
 Acute MI particularly acute inferior wall MI.
 Myocarditis.
 Electrolyte disturbances (e.g hypokalemia, hypomagnesemia)
 Drugs(esp.those drugs that increase the refractory time of the AV
node, there by slowing conduction).
 Drugs that most commonly causes first degree AV block include
following:
 Class 1c antiarrhythmias (e.g Quinidine, procainamide,
disopyramide)
 Class2c antiarrhythmias (e.g Flecainide, encainide)
 Class3c antiarrhythmias (Beta blockers)

9. SECOND DEGREE HEART BLOCK
 Second degree heart block implies intermittent conduction, some impulses
from the atria are conducted to ventricles whereas others are not.
 CAUSES:
 Inferior wall MI.
 Drugs like digitalis, beta blockers, calcium antagonists.
 Hyperkalemia in well trained athelets during sleep.
 Myocarditis
 TYPES OF SECOND DEGREE HEART BLOCK:
 There are three types of second degree heart block.
 Mobitz type 1
 Mobitz type 2
 2:1 block

10. MOBITZ TYPE 1
 In this condition, there is progressive lengthening of successive PR
intervals followed by a dropped beat (non conducted P). This is also
known as wenckebach’s phenomenon.
 In this AV block, there is conduction defect in AV node and AV
conduction time (PR interval) progressively lengthens before blocked
beat pulse is clinically irregular.
 Prognosis is good in first degree and in Mobitz type 1,since reliable
alternative pacemaker arise from AV junction below the block, if
complete heart block develops.
 Site of block is AV node. QRS complex is normal in morphology
because there is no delay in interventricular depolarization.

11. MOBITZ TYPE 2
 In this condition, the PR interval of the conducted impulses remain
constant but some P waves are not conducted (i.e more P waves
than QRS complexes)
 Site of block is infranodal in location and QRS complexes are wide.
Mobitz type 2 AV block is abrupt and is not preceded by
lengthening of AV conduction time. It is usually due to block within
the bundle of His.
 Mobitz 2 block is almost always due to organic heart disease, in
case it proceeds to complete heart block.
2:1 BLOCK
 It may represent as either type for type 2 AV block in which there
are two P waves to each QRS complex and therefore, called 2:1
block.
 If PR interval is prolonged and QRS complex is narrow then it is
type1 second degree heart block.
 If PR interval is normal then QRS complex is wide, it is called second
degree AV block

12. THIRD DEGREE(COMPLETE) HEART BLOCK
 Third degree heart block is an advanced form of block. No impulse
from atria reaches the ventricles. Cardiac action is maintained by an
escape rhythm.
 CAUSES:
 CONGENITAL
 ACQUIRED
 Idiopathic fibrosis
 MI/Ischemia
 INFECTIONS: Infective endocarditis, Chagas disease, Lyme’s
disease.
 INFILTRATION: Sarcoidosis, Amyloidosis, Neoplasia
 DRUGS: Digioxin, Beta blockers, Amiodaron
 TRAUMA: Cardiac surgery.
 CONNECTIVE TISSUE DISEASE: SLE,RA

13. MECHANISM
 Escape rhythm arising in the bundle of His produces narrow QRS
complex at the rate of 50-60beats/min.Escape rhythm arising below
the His bundle produces broad complexes and at rate of 15-
40beats/min.
 It is more advanced form of heart block due to lesion at the level of
bundle of His or more often distally in Purkinjie system and
associated with bilateral bundle branch block. QRS complex is wide
and ventricular rate is slower. Transmission of atrial pulses through
AV node is completely blocked and a ventricular rate, usually less
than 45beats/min.
 In chronic complete heart block, pulse is slow (30-40min) regular
and does not vary with exercise

14. Stokes-Adams Attacks
 Episodes of ventricular asystole may occur during periods of
transition from partial to complete heart block lasting several
seconds to minutes. These episodes may cause cardiac syncope
called Stokes-Adams attacks.
 These attacks often occur without warning, there is rapid loss of
consciousness and pt. may fall.
 Convulsions may occur, if heart does not begin to beat within about
10sec and death will result, if arrest is prolonged.

15. BUNDLE BRANCH BLOCKS AND
HEMIBLOCKS

16. BUNDLE BRANCH BLOCK
 In normal heart, each electrical impulses from the atria is
conducted through the AV node to the bundle of His, from which it
is transmitted to the ventricles by the right and left bundle
branches.
 TYPES
 Left bundle branch block
 Right bundle branch block

17. LEFT BUNDLE BRANCH BLOCK
 In LBBB, left bundle branch no longer conducts electrical activity. The
electrical impulse thus enters right bundle branch block and is carried to
right ventricle. From there, it finally spreads to left ventricle. The two
ventricles no longer receive the electrical impulse simultaneously. First, the
Rt. ventricle receives the electrical impulse, then left.
 CAUSES
 Hypertrophy, dilatation or fibrosis LV myocardium.
 Ischemic heart disease.
 Cardiomyopathies.
 Advanced valvular heart disease.
 Toxic, inflammatory changes.
 Hyperkalemia.
 Digitalis toxicity.
 Degenerative disease of conducting system (Lenegre disease).

18. TYPES OF LBBB
• The LBBB can be divided into two fascicles:
 Anterior Fascicles.
 Posterior Fascicles.
 Conduction system is composed of three fascicles:
 Right Bundle Fascicle.
 Left Anterior Fascicle.
 Left Posterior Fascicle.

19. RIGHT BUNDLE BRANCH BLOCK
 RBBB results from a defect in heart’s electrical conducting system.
There is a delay in or failure of transmission of electrical impulses
down the right bundle of heart. As a result , the Rt. Ventricle
depolarizes by means of cell- to- cell conduction. These impulses
spread more slowly than usual from inter ventricular septum to Rt.
Ventricle.This delay in conduction results in characteristic ECG
pattern, which is wide and notched QRS. Although conduction down
the Rt. branch is delayed ,conduction down the Lt. branch is normal.
As a result, the interventricular septum and Lt. ventricle in normal
fashion.
 TYPES
There are two types.
 Complete RBBB.
 Incomplete RBBB.

20. CAUSES OF RBBB
 Following are the causes of RBBB.
 After repair of VSD.
 After Rt.ventriculotomy.
 Right Venticular hypertrophy.
 Ebstein’s anomaly.
 Large ASD or AV cushion defect.
 Right ventricular dysplasia.
 Brugada syndrome.
 Congenital absence or atrophy of bundle branch.
 After CABG and in transplanted heart.

21. HEMIBLOCK
 DEFINITION:
When there is blockage in anterior or posterior division of left
bundle branch, it is called hemiblock.
BIFASCICULAR BLOCK:
 RBBB plus left anterior or posterior hemiblock.
 In bifascicular and trifascicular block there are more chances to
progress to complete heart block.
TRIFASCICULAR BLOCK:
 RBBB + Hemiblock + First degree heart block.

22. THANK YOU