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Sick sinus syndrome-2


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Rawalpindi Medical college

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Sick sinus syndrome-2

  2. 2. 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.
  3. 3. 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.
  4. 4. 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. 
  5. 5. 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.
  6. 6. 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 
  7. 7. 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)    
  8. 8. 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
  9. 9. 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 .
  10. 10. 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
  11. 11.  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
  12. 12. 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 1540beats/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
  13. 13. 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. 15. 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
  16. 16. 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).
  17. 17. 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.
  18. 18. 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.
  19. 19. 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.
  20. 20. 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.
  21. 21. THANK YOU