Interpretation And Interpretation And management of the ECGmanagement of the ECG

In In Bradyarrhythmias And Heart Bradyarrhythmias And Heart

BlocksBlocks

DR.Tareq M.Al-MuflehiDR.Tareq M.Al-MuflehiINTERVENTIONAL CARDIOLOGISTINTERVENTIONAL CARDIOLOGIST

. .Sinus BradycardiaSinus Bradycardia.. . .Junctional rhythmJunctional rhythm..

. .Idioventricular rhythmIdioventricular rhythm.. . .Sinus node dysfunction or Sinus node dysfunction or

(sick sinus syndrom)(sick sinus syndrom).. . .AV-blocksAV-blocks..

. .Heart block with acute MIHeart block with acute MI.. . .Intraventricular conduction Intraventricular conduction

abnormalities(IVCAs)abnormalities(IVCAs).. . .MI in the presence of BBBMI in the presence of BBB..

BLOOD SUPPLY OF THE CARDIAC BLOOD SUPPLY OF THE CARDIAC CONDUCTION SYSTEMCONDUCTION SYSTEM

The blood supply to the sinoatrial node is The blood supply to the sinoatrial node is from the sinus node artery which arises from the sinus node artery which arises from the proximal RCA in 55% of the from the proximal RCA in 55% of the population and in 35% from the circumflex population and in 35% from the circumflex artery and in 10% from both RCA and CX.artery and in 10% from both RCA and CX.

The AV-node receives its blood supply The AV-node receives its blood supply from the AV- nodal artery which arises from the AV- nodal artery which arises from the PDA of RCA in 80% of population from the PDA of RCA in 80% of population and 10% from circumflex artery and 10% and 10% from circumflex artery and 10% from both arteries .from both arteries .

Collateral blood supply from the LAD Collateral blood supply from the LAD artery makes the AV- node somewhat less artery makes the AV- node somewhat less prone to ischemic damage than the prone to ischemic damage than the sinoatrial node .sinoatrial node .

The AV- nodal artery and the first septal The AV- nodal artery and the first septal perforator of the LAD artery offer dual perforator of the LAD artery offer dual blood supply to the atrioventricular (His) blood supply to the atrioventricular (His) bundle and RBB .bundle and RBB .

The anterior fascicle of the LBB receives The anterior fascicle of the LBB receives blood from the other septal perforating blood from the other septal perforating branchs of the LAD .branchs of the LAD .

The posterior fascicle has a dual blood The posterior fascicle has a dual blood supply from the septal perforating branchs supply from the septal perforating branchs of the LAD and branchs of the PDA of of the LAD and branchs of the PDA of RCA. RCA.

Cardinal features of normal sinus Cardinal features of normal sinus rhythmrhythm

.. The P wave is upright in leads The P wave is upright in leads 1,2,3 and AVF 1,2,3 and AVF

.. The P wave is negative in lead The P wave is negative in lead AVRAVR

.. Each P wave is followed by a Each P wave is followed by a QRS complexQRS complex

.. The heart rate is 60-100 beat\ The heart rate is 60-100 beat\ minmin

NSR Parameters

• Rate 60 - 100 bpm

• Regularity regular

• P waves normal

• PR interval 0.12 - 0.20 s

• QRS duration 0.04 - 0.12 s

Any deviation from above is sinus tachycardia, sinus bradycardia or an arrhythmia

Pacemakers of the Heart

• SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.

• AV Node(Junctional) - Back-up pacemaker with an intrinsic rate of 40 -60 beats/minute.

• Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 45 bpm.

Normal Impulse ConductionNormal Impulse Conduction

Sinoatrial nodeSinoatrial node

AV nodeAV node

Bundle of HisBundle of His

Bundle BranchesBundle Branches

Purkinje fibersPurkinje fibers

Impulse Conduction & the Impulse Conduction & the ECGECG

Sinoatrial nodeSinoatrial node

AV nodeAV node

Bundle of HisBundle of His

Bundle BranchesBundle Branches

Purkinje fibersPurkinje fibers

Sinus Sinus bradycardiabradycardia

Normal resting heart rate has Normal resting heart rate has been defined as 60-100 bpm.been defined as 60-100 bpm.

Bradicardia is defined as Bradicardia is defined as ventricular rate less than 60 ventricular rate less than 60 bpm.bpm.

It should be noted some It should be noted some otherwise healthy individuals otherwise healthy individuals have resting heart rate less than have resting heart rate less than 60 bpm. The greatest variation is 60 bpm. The greatest variation is found in athletes primarily from found in athletes primarily from increase parasympathetic tone. increase parasympathetic tone.

Sinus bradycardia exists when a P Sinus bradycardia exists when a P wave precedes each QRS complex. wave precedes each QRS complex. this QRS complex is usually narrow this QRS complex is usually narrow (less than 0.120 seconds ) because (less than 0.120 seconds ) because the impulse originates from a the impulse originates from a supraventricular focus .supraventricular focus .

There are specific incidences in There are specific incidences in which, despite the supraventricular which, despite the supraventricular focus, the QRS is widened (greater focus, the QRS is widened (greater than 0.12 seconds ) an example of than 0.12 seconds ) an example of this is a BBB (right or left ) in which this is a BBB (right or left ) in which the QRS is wide but each QRS the QRS is wide but each QRS complex is still considered by a P- complex is still considered by a P- wave .wave .

Sinus BradycardiaSinus Bradycardia

Etiology:Etiology: SA node is depolarizing SA node is depolarizing slower than normal, impulse is slower than normal, impulse is conducted normally (i.e. normal PR conducted normally (i.e. normal PR and QRS interval).and QRS interval).

Sinus bradycardia--etiologiesSinus bradycardia--etiologies

Normal agingNormal aging15-25% Acute MI, esp. affecting inferior 15-25% Acute MI, esp. affecting inferior

wallwallHypothyroidism, infiltrative diseasesHypothyroidism, infiltrative diseases

(sarcoid, amyloid)(sarcoid, amyloid)Hypothermia, hypokalemiaHypothermia, hypokalemiaSLE, collagen vasc diseasesSLE, collagen vasc diseasesSituational: micturation, coughingSituational: micturation, coughingDrugsDrugs: beta-blockers, digitalis, calcium : beta-blockers, digitalis, calcium

channel blockers, amiodarone, cimetidine, channel blockers, amiodarone, cimetidine, lithiumlithium

History: History: Sinus bradycardia is most often asymptomatic. Sinus bradycardia is most often asymptomatic.

However, symptoms may include the following:However, symptoms may include the following:SyncopeSyncopeDizzinessDizzinessLightheadednessLightheadednessChest painChest painShortness of breathShortness of breath

Pertinent elements of the history include the Pertinent elements of the history include the following:following:Previous cardiac history (eg, myocardial infarction, Previous cardiac history (eg, myocardial infarction,

congestive heart failure, valvular failure)congestive heart failure, valvular failure)MedicationsMedicationsToxic exposuresToxic exposuresPrior illnessesPrior illnesses

Physical: Physical: Cardiac auscultation and palpation of Cardiac auscultation and palpation of

peripheral pulses reveal a slow, regular heart peripheral pulses reveal a slow, regular heart rate.rate.

The physical examination is generally The physical examination is generally nonspecific, although it may reveal the nonspecific, although it may reveal the following signs:following signs:Decreased level of consciousnessDecreased level of consciousnessCyanosisCyanosisPeripheral edemaPeripheral edemaPulmonary vascular congestionPulmonary vascular congestionDyspneaDyspneaPoor perfusionPoor perfusionSyncopeSyncope

Lab Studies: Lab Studies: Laboratory studies may be helpful if the cause of the Laboratory studies may be helpful if the cause of the

bradycardia is thought to be related to electrolytes, drug, or bradycardia is thought to be related to electrolytes, drug, or toxins. toxins.

Reasonable screening studies, especially if the patient is Reasonable screening studies, especially if the patient is symptomatic and this is the initial presentation, include the symptomatic and this is the initial presentation, include the following:following:

ElectrolytesElectrolytesGlucoseGlucoseCalciumCalciumMagnesiumMagnesiumThyroid function testsThyroid function testsToxicologic screenToxicologic screen

Imaging Studies:Imaging Studies: Routine imaging studies are rarely of value in the absence of Routine imaging studies are rarely of value in the absence of

specific indications.specific indications. Other Tests: Other Tests:

12-lead ECG may be performed to confirm the diagnosis.12-lead ECG may be performed to confirm the diagnosis.

Sinus BradycardiaSinus Bradycardia

HR< 60 bpm; every QRS narrow, preceded by p HR< 60 bpm; every QRS narrow, preceded by p wavewave

Can be normal in well-conditioned athletesCan be normal in well-conditioned athletesHR can be<30 bpm in children, young adults HR can be<30 bpm in children, young adults

during sleep, with up to 2 sec pausesduring sleep, with up to 2 sec pauses

Sinus bradycardia--treatmentSinus bradycardia--treatment

No treatment if asymptomaticNo treatment if asymptomaticOfficeOffice: Evaluate medicine regimen: Evaluate medicine regimen——stop stop

all drugs that may causeall drugs that may causeBradycardia associated with MI will often Bradycardia associated with MI will often

resolve as MI is resolving; will not be the resolve as MI is resolving; will not be the sole sxs of MIsole sxs of MI

ERER: Atropine if hemodynamic compromise, : Atropine if hemodynamic compromise, syncope, chest painsyncope, chest pain

PacingPacing

Junctional Junctional rhythmrhythm

Junctional rhythm is another Junctional rhythm is another example of a supraventricular example of a supraventricular rhythm in which the QRS complex is rhythm in which the QRS complex is usually narrow (less than 0.12 usually narrow (less than 0.12 seconds ) and regular this is seconds ) and regular this is distinguished from sinus bradycardia distinguished from sinus bradycardia on ECG because it is not associated on ECG because it is not associated with preceding P- wave, a junctional with preceding P- wave, a junctional escape rate is usually 40- 60 bpm a escape rate is usually 40- 60 bpm a junctional rhythm with a rate slower junctional rhythm with a rate slower than 40 bpm is termed a junctional than 40 bpm is termed a junctional bradycardia and a rate faster than 60 bradycardia and a rate faster than 60 bpm is termed an accelerated bpm is termed an accelerated junctional rhythm or a junctional junctional rhythm or a junctional tachicardia .tachicardia .

There are times when there are p waves There are times when there are p waves evident on the ECG of patients who have a evident on the ECG of patients who have a junctional rhythm but unlike normal sinus junctional rhythm but unlike normal sinus rhythm or sinus bradycardia thes P waves rhythm or sinus bradycardia thes P waves are not conducted in an anterograde are not conducted in an anterograde fashion these are termed P waves and fashion these are termed P waves and may appear before during or after the QRS may appear before during or after the QRS complex depending on when the atrium is complex depending on when the atrium is captured by the impules emanating from captured by the impules emanating from the AV junction As in sinus bradycardia, the AV junction As in sinus bradycardia, there are also times in which the QRS is there are also times in which the QRS is widened because of right or left BBB.widened because of right or left BBB.

Junctional bradycardiaJunctional bradycardia Junctional bradycardia is treated in the Junctional bradycardia is treated in the

same way as sinus bradycardia .same way as sinus bradycardia . Junctional bradyardia is a frequent Junctional bradyardia is a frequent

accompaniment of reperfusion and indeed accompaniment of reperfusion and indeed can be used as a marker of successful can be used as a marker of successful reperfusion. reperfusion.

Therapy of junctional rhythm secondary Therapy of junctional rhythm secondary to sinoatrial node, failure of AV-block is as to sinoatrial node, failure of AV-block is as the treatment of atrioventricular the treatment of atrioventricular conduction disturbances.conduction disturbances.

Accelerated Junctional Accelerated Junctional RhythmRhythm

EtiologyEtiology

Accelerated junctional rhythm is seen in Accelerated junctional rhythm is seen in approximately 10% of patiens with MI more than approximately 10% of patiens with MI more than half these patients have inferior MI and about on- half these patients have inferior MI and about on- third have anterior MI.third have anterior MI.

Digitalis toxicity by itself does not seen to cause Digitalis toxicity by itself does not seen to cause accelerated junctional rhythm, as evidence in accelerated junctional rhythm, as evidence in persons with normal hearts who take accidental persons with normal hearts who take accidental overdoses of digoxin.overdoses of digoxin.

Concomitant heart disease is required to develop Concomitant heart disease is required to develop accelerated junctional rhythm.accelerated junctional rhythm.

.. The difference between accelerated Junctional The difference between accelerated Junctional

rhythm and third- degree AV- block is the fact that rhythm and third- degree AV- block is the fact that the ventricular rate is faster than the atrial rate in the ventricular rate is faster than the atrial rate in accelerated junctioal rhythm and slower than the accelerated junctioal rhythm and slower than the

atrial rate in third- degree AV- blockatrial rate in third- degree AV- block. .

other causes of accelerated other causes of accelerated junctional rhythm are valve surgery, junctional rhythm are valve surgery, acute rheumatic fever, direct current acute rheumatic fever, direct current cardioversion, cardiac cath, COPD, cardioversion, cardiac cath, COPD, Amyliodosis and uremia with Amyliodosis and uremia with hyperkalemia.hyperkalemia.

The distinguishing characteristic of The distinguishing characteristic of accelerated junctional rhythm is the accelerated junctional rhythm is the atrioventricular dissociation and atrioventricular dissociation and changing PR interval. changing PR interval.

TreatmentTreatment

Patients with accelerated junctional Patients with accelerated junctional rhythm do not usually require therapy for rhythm do not usually require therapy for the arrhythmia, although mangement of the arrhythmia, although mangement of the underlying cause is indicated.the underlying cause is indicated.

Suppression of accelerated junctional Suppression of accelerated junctional rhythm maybe achieved by increasing the rhythm maybe achieved by increasing the atrial rate with drugs (eg, Atropin, atrial rate with drugs (eg, Atropin, Adrenergics) or pacing.Adrenergics) or pacing.

Digoxin - induced accelerated junctional Digoxin - induced accelerated junctional rhythm is an indication to stop digoxin but rhythm is an indication to stop digoxin but does not usually require administration of does not usually require administration of digoxin _ specific fab fragments.digoxin _ specific fab fragments.

Idioventricular Idioventricular rhythmrhythm

Idioventricular rhythms are regular Idioventricular rhythms are regular but unlike sinus bradycardia or but unlike sinus bradycardia or junctional rhythm, they are always junctional rhythm, they are always characterized by a wide QRS characterized by a wide QRS complex because their origin lies complex because their origin lies some where within the ventricles on some where within the ventricles on ECG the rate is usually 20- 40 bpm ECG the rate is usually 20- 40 bpm except for accelerated idioventricular except for accelerated idioventricular rhythm (rate greater than 40 bpm ).rhythm (rate greater than 40 bpm ).

Idioventricular rhythm (IVR)Idioventricular rhythm (IVR)

IVR is usually too slow to maintain IVR is usually too slow to maintain adequate cardiac output and treatment is adequate cardiac output and treatment is more frequently needed.more frequently needed.

The patient depends on these complexes The patient depends on these complexes for survival.for survival.

Suppressive treatment (e.g. lidocaine) Suppressive treatment (e.g. lidocaine) may therefore lead to asystole .may therefore lead to asystole .

Atropine and pacing are usually required, Atropine and pacing are usually required, as well as correction of the underlying as well as correction of the underlying cause (AMI , complete heart block , cardiac cause (AMI , complete heart block , cardiac , tamponade , hemorrhage ) . , tamponade , hemorrhage ) .

CPR may be needed as well. CPR may be needed as well.

Accelerated Accelerated Idioventricular rhythm Idioventricular rhythm (AIVR)(AIVR) AIVR is a form of VT and occurs as a rule in AIVR is a form of VT and occurs as a rule in

patients with cardiac disease ( almost in IHD ).patients with cardiac disease ( almost in IHD ). AMI and digitalis toxicity are the common AMI and digitalis toxicity are the common

precipitating events. (It is common 48h after MI).precipitating events. (It is common 48h after MI). This rhythm is also commonly seen when This rhythm is also commonly seen when

thrombolytics are given for an AMI, and if it thrombolytics are given for an AMI, and if it occurs, thrombolytics should be continued. (It occurs, thrombolytics should be continued. (It usually means successful reperfusion).usually means successful reperfusion).

The mechanism is believed to be secondary to an The mechanism is believed to be secondary to an ectopic ventricular focus (usually in the ectopic ventricular focus (usually in the reperfusion zone) that accelerates beyond the reperfusion zone) that accelerates beyond the intrinsic sinus rate.intrinsic sinus rate.

The P- wave may come closer and closer The P- wave may come closer and closer to the QRS complex at the same time the to the QRS complex at the same time the shape of the QRS complex changes to its shape of the QRS complex changes to its wide ventricular contour, and then wide ventricular contour, and then disappears into it .disappears into it .

It is usually regular, has a rate of 60- 120 It is usually regular, has a rate of 60- 120 bpm, and is of little clinical significance.bpm, and is of little clinical significance.

Treatment for AIVR is rarly necessary.Treatment for AIVR is rarly necessary. With severe symptoms or hemodynamic With severe symptoms or hemodynamic

compromise, Atropine or a trial pacing can compromise, Atropine or a trial pacing can be used to stimulate the sinus rhythm to be used to stimulate the sinus rhythm to overdrive the ectopic focus.overdrive the ectopic focus.

Treatment can also be considerd when Treatment can also be considerd when AIVRAIVR occurs with VT. Suppression of the occurs with VT. Suppression of the dysrhythmia can also be undertaken with dysrhythmia can also be undertaken with thethe same drugs used to treat VT.same drugs used to treat VT.

.. Sinus BradycardiaSinus Bradycardia.... Junctional rhythmJunctional rhythm..

.. Idioventricular rhythmIdioventricular rhythm.... Sinus node dysfunction or Sinus node dysfunction or

(sick sinus syndrom)(sick sinus syndrom).... AV-blocksAV-blocks..

.. Heart block with acute MIHeart block with acute MI.... Intraventricular conduction Intraventricular conduction

abnormalities(IVCAs)abnormalities(IVCAs).... MI in the presence of BBBMI in the presence of BBB..

SINUS NODE SINUS NODE DYSFUNNCTION DYSFUNNCTION OR "SICK SINUS OR "SICK SINUS

SYNDROMESYNDROME " "

""

sick sinus syndrom is a sick sinus syndrom is a collective term that includes a collective term that includes a range of SA node dysfunction range of SA node dysfunction that manifests in various that manifests in various different ways on ECG including :different ways on ECG including :

.. Persistent inappropriate sinus Persistent inappropriate sinus

bradycardia .bradycardia . .. Intermittent sinus pause/ Intermittent sinus pause/

arrest.arrest. .. sinoatrial exit block. sinoatrial exit block. .. AV junctional (escape ) AV junctional (escape )

rhythm.rhythm. .. Tachy - brady syndrome. Tachy - brady syndrome.

Sick Sinus SyndromeSick Sinus Syndrome

Patients are usually elderly Patients are usually elderly and present with and present with lightheadedness and/or lightheadedness and/or syncope, but it can also syncope, but it can also manifest as angina, dyspnea, manifest as angina, dyspnea, and palpitations. and palpitations.

About 50% of people with About 50% of people with SSS also display some degree SSS also display some degree of dysfunction of the AV nodeof dysfunction of the AV node

Sinus pause and sinus arrest are characterized Sinus pause and sinus arrest are characterized by the failure of the SA node to form an impulse by the failure of the SA node to form an impulse although sinus pause refers to a brief failure and although sinus pause refers to a brief failure and sinus arrest refers to a more prolonged failure of sinus arrest refers to a more prolonged failure of the SA node, there are no universally accepted the SA node, there are no universally accepted definitions to differentiate the two.definitions to differentiate the two.

Because of this, they are often used Because of this, they are often used interchangeably to describe the same cardiac interchangeably to describe the same cardiac event.event.

On ECG there is an absence of the P-QRS-T On ECG there is an absence of the P-QRS-T complex resulting in a pause of indeterminate complex resulting in a pause of indeterminate length. The sinus node most often resumes length. The sinus node most often resumes pacemaker activity and a normal sinus rhythm is pacemaker activity and a normal sinus rhythm is seen. In cases in witch it fails, however the seen. In cases in witch it fails, however the escape rhythm seen is usually from the AV node. escape rhythm seen is usually from the AV node. If the AV node fails, the next pacemaker to take If the AV node fails, the next pacemaker to take would result in an idioventricular rhythm. If all of would result in an idioventricular rhythm. If all of these fail to generate an ascape rhythm, the these fail to generate an ascape rhythm, the result is asystole .result is asystole .

Mechanism of sinus node Mechanism of sinus node dysfunction includes decreased dysfunction includes decreased automaticity of sinus nodal tissue automaticity of sinus nodal tissue and sinatrial (SA) exit block.and sinatrial (SA) exit block.

In SA exit block, rhythmic In SA exit block, rhythmic depolarization continues to occur , depolarization continues to occur , but the impulse is delayed or blocked but the impulse is delayed or blocked in the perinodal tissue.in the perinodal tissue.

Diagnosis by surface ECG is difficult Diagnosis by surface ECG is difficult because external leads do not because external leads do not directly record activity within the directly record activity within the sinus node.sinus node.

Sinus bradycardia associated with Sinus bradycardia associated with sinus node dysfunction is a marked, sinus node dysfunction is a marked, persistent sinus bradycardia , with persistent sinus bradycardia , with sinus rate less than 40 bpm and sinus rate less than 40 bpm and pauses of greater than 2s.pauses of greater than 2s.

A sinoatrial pause greater than 3s A sinoatrial pause greater than 3s following carotid massage may following carotid massage may indicate sick sinus syndrome. indicate sick sinus syndrome.

Sick Sinus SyndromeSick Sinus Syndrome

Sinus bradycardia (rate of ~43 bpm) with a sinus pause

Sinoatrial (SA) blocks result when Sinoatrial (SA) blocks result when there is an abnormality between the there is an abnormality between the conduction of the impulse from conduction of the impulse from hearts normal pacemaker (SA node) hearts normal pacemaker (SA node) to the surrounding atrium.to the surrounding atrium.

AS with AV- block SA block is AS with AV- block SA block is characterized as first, second and characterized as first, second and third-degree, with second- degree third-degree, with second- degree blocks subclassified as type I and blocks subclassified as type I and type II.type II.

Tachycardia-Bradycardia Tachycardia-Bradycardia SyndromeSyndrome

Common variant of sick sinus Common variant of sick sinus syndrome severe bradycardia syndrome severe bradycardia alternates with paroxysmal alternates with paroxysmal tachycardias, most often atrial tachycardias, most often atrial fibrillation. fibrillation.

There is usually a prolonged pause in There is usually a prolonged pause in the cardiac rhythm following the cardiac rhythm following cessation of the tachyarrhythmia. cessation of the tachyarrhythmia.

Tachycardia-Bradycardia Tachycardia-Bradycardia SyndromeSyndrome

Abrupt termination of atrial flutter with variable AV block, followed by sinus arrest with a junctional escape beat.

Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7th ed., 2005.

Etiologies of Sick Sinus Etiologies of Sick Sinus SyndromeSyndrome

More CommonMore Common

Sinus node firbosisSinus node firbosis

Atherosclerosis of the Atherosclerosis of the SA arterySA artery

Congenital heart Congenital heart diseasedisease

Excessive vagal toneExcessive vagal tone

Drugs Drugs

Less CommonLess Common

Familial SSS (due to Familial SSS (due to mutations in SCN5A)mutations in SCN5A)

Infiltrative diseasesInfiltrative diseases

PericarditisPericarditis

Lyme diseaseLyme disease

HypothyroidismHypothyroidism

Rheumatic fever Rheumatic fever

Sick sinus syndrome--Sick sinus syndrome--treatmenttreatment

Address and treat cardiac conditionsAddress and treat cardiac conditionsReview med list, TSHReview med list, TSHPacemaker for most is requiredPacemaker for most is required

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