avn bradycardia mediated

Dr.ahmed Taha Hussein

M.Sc. Cardiology

Zagzig university

Those who suffer from frequent and strongfaints without any manifest cause diesuddenly“ Hippocrates (460 - 375 BC)

Micheal Bernhard Valentini (1713)

Tadpole shaped 2 X 5mm

lies beneath the RAendocardium at theapex of the triangle ofKoch.

blood supply to theAVN predominantlycomes from a branchof the right coronaryartery in 85% to 90%of patients and fromthe circumflex arteryin 10% to 15%

Low densityNa channelsHigh density

L-type Cachannel

connects with the distalpart of the compact AVN,perforates the centralfibrous body, andpenetrates themembranous septum,along the crest of the leftside of the interventricularseptum, for 1 to 2 cm andthen divides into the rightand left bundle branches.

dual blood supply frombranches LAD , PDA .

The main function is to delay conduction ofimpulse propagated from atrium to ventricleallowing diastolic time enough for ventricularfilling and atrial contraction.

limit the number of impulses conducted fromthe atria to the ventricles.

-ve dromotropic response: activating IK(Ach,Ado)

+ve dromotropic response : activating L-typeCa channels

AV conduction isrepresented on thesurface ECG byPR interval(120-200 ms).

PR= (ARA –Ahiss)+(A-H) .

PRinterval

can be defined as transient or permanentdelay or interruption in the transmission of animpulse from the atria to the ventricles causedby an anatomical or functional impairment inthe conduction system.

Congenital …1/22000 LUPUS-mother , CHD. Acquired : drug-induced CAD Rheumatic diseases( AS, Reiter’s, SLE..) Infiltrative diseases(amyloidosis , sarcoidosis..) Infectious (viral , chagas, TB) Neuromyopathies . Iatrogenic ( cardiac surgery , RFA) Vagally mediated Long QT syndromes .

LEV’S DISEASE LENEGRE’S DISEASE

Fibrocalcification ofcardiac cytoskeleton

MAC , Aortic Scleorsis

Primary scelerosingdisease of theconductive system.

In involvement of thecytoskeleton

For diagnostic and prognostic value …. AV-block is divided into nodal block Infranodal block . Diagnosis achieved by : ECG ( PR interval , P-R

wave relation , QRS duration) Autonomic modulation exercise testing . EP Study .

Incomplete AV block includesa. first-degree AV blockb. second degree AV blockc. advanced AV block

Complete AV block,also known as third degreeAV block

Proximal to, in, or distal to the His bundle intheatrium or AV node

All degrees of AV block may be intermittent orpersistent

PR interval is prolonged 0.21-0.40 seconds, but no R-R intervalchange.

First-degree atrioventricular block caused by intranodalconduction delay

First-degree atrioventricular block secondary to His-Purkinjesystem (HPS) disease

First-degree atrioventricular block caused by intraatrialconduction delay

There is intermittent failure of thesupraventricular impulse to be conducted tothe ventricles

Some of the P waves are not followed by a QRScomplex.The conduction ratio (P/QRS ratio)may be set at 2:1,3:1,3:2,4:3,and so forth

Type I also is called Wenckebachphenomenon or Mobitz type I and representsthe more common type

Type II is also called Mobitz type II

typical periodicityProgressive lengthening of the PR interval until a Pwave is blocked2.Progressive shortening of the RR interval until a Pwave is blocked3.RR interval containing the blocked P wave is shorterthan the sum of two PP intervals

Infra-Hisian second-degree Wenckebach trioventricular (AV) block. Atrialpacing in a patient with a normal prolonged atrial–His bundle interval(AH) but prolonged His bundle–ventricular interval (HV) and rightbundle branch block (RBBB)

ECG findings1.Intermittent blocked P waves2.PR intervals may be normal or prolonged,butthey remain constant3.When the AV conduction ratio is 2:1,it isoften impossible to determine whether thesecond-degree AV block is type I or II4. A long rhythm strip may help

When the AV conduction ratio is 3:1 or higher,therhythm is called advanced AV blocked

A comparison of the PR intervals of the occasionalcaptured complexes may provide a clue

If the PR interval varies and its duration is inverselyrelated to the interval between the P wave and itspreceding R wave (RP), type I block is likely

A constant PR interval in all captured complexessuggests type II block

There is complete failure of thesupraventricular impulses to reach theventricles

The atrial and ventricular activities areindependent of each other.

Ventriculophasic Sinus Arrhythmia : intermittent differences in the P-P intervals

based on their relationship to the QRS complex.

In patients with sinus rhythm and completeAV block, the PP and RR intervals are regular,but the P waves bear no constant relation to theQRS complexes

Exclude other phenomena

Sinus rhythm with normal atrioventricular (AV) conduction. Frequentpremature atrial complexes (PACs; A′) are observed in a bigeminal pattern

HB ectopy that fail to conduct to both Atria andventricle .

Appear like type 2 AV block . ECG clues : (1) abrupt, unexplained prolongation of the PR

interval . (2) the presence of apparent Mobitz type II block in

the presence of a normal QRS (3) the presence of types 1 and 2 AV block in the

same tracing (4) the presence of manifest junctional extrasystoles

elsewhere in the tracing.

Atrial tachycardia with subsidiary escape focusfrom AV junction or ventricle .

Accelerated idioventricular rhythm . Vtach.

Echo beat :

can manifest as “group beating” and bemisdiagnosed as Wenckebach block.

ECG clues: PR interval , P-wave morphology. Atrial tachyarrhythmia with variable AV

conduction .

Pacing is the mainstay of treatment forsymptomatic AV block .

Identifying transient or reversible causes forAV conduction disturbances is the first step inmanagement. Withdrawal of any offendingdrugs, correction of any electrolyteabnormalities, or treatment of any infectiousprocesses should be considered prior topermanent pacing therapy.