Properties of cardiac cellsAutomaticity• Ability to initiate an impulse spontaneously andcontinuously.Excitability.• Ability to be electrically stimulated.Conductivity• Ability to transmit an impulse along a membrane inan orderly manner.Contractility• Ability to respond mechanically to an impulse.
Pacemakers of the Heart• SA Node - Dominant pacemaker with anintrinsic rate of 60 - 100 beats/minute.• AV Node - Back-up pacemaker with anintrinsic rate of 40 - 60 beats/minute.• Ventricular cells - Back-up pacemaker withan intrinsic rate of 20 - 45 bpm.
Impulse Conduction & the ECGSinoatrial nodeAV nodeBundle of HisBundle BranchesPurkinje fibers
The “PQRST”• P wave - Atrialdepolarization• T wave - Ventricularrepolarization• QRS - Ventriculardepolarization
The PR IntervalAtrial depolarization+delay in AV junction(AV node/Bundle of His)(delay allows time forthe atria to contractbefore the ventriclescontract)
The ECG Paper• Horizontally– One small box - 0.04 s– One large box - 0.20 s• Vertically– One large box - 0.5 mV
ECG Composed of Waves And ComplexesP- WAVE QT- INTERVALQRS- COMPLEX PR- INTERVALT- WAVE ST- SEGMENT
Criterias of a normal heart rhythm1. Presence of one upright and consistent-appearing P wave before each QRScomplex.2. P-R interval between 0.12-0.20 seconds3. A consistent appearing QRS complex ofless than 0.12 seconds.4. Consistent R-R interval5. A heart rate between 60-100 beats/minute6. The ST segment should be isoelectrical
Arrhythmias• It is a disturbance in therhythmic patterns of the heart.Results from abnormalimpulse initiation, abnormalconduction or both mechanismtogether.
Four Steps to Identify Arrhythmias1- Begin by labeling the P wave, QRScomplex, T wave, PR interval, and QTinterval.2- Calculate the atrial and ventricular heartrates.3- Determine if the rhythm is regular orirregular.4- Evaluate the waveform of the ECG indetail for additional clues:
Mechanisms Of ArrhythmiasArrhythmias result from1-Abnormal impulse initiation and2-Abnormal impulse conduction.
Mechanisms Of ArrhythmiasThe major mechanisms of arrhythmias areABNORMAL IMPULSE INITIATIONEnhanced normal automaticityAbnormal automaticityTriggered activity due to afterdepolarizationABNORMAL IMPULSE CONDUCTIONConduction blocksReentry12
Enhanced normal automaticity• Automaticity is defined as the ability of a cellto independently initiate an action potential.
Classification Of Arrhythmias• Disorders of ImpulseGeneration• Disorders of ImpulseConduction
II. Disorder of impulse conduction• S.A. Block• First degree AV Block• Second Degree A.V.Block» Mobitz type I» Mobitz type II• Third Degree or Complete A.V Block
Mechanism responsible for phase 4depolarization1. Decreased outward permeability topotassium2. Increased inward permeability to sodium3. Reduced sodium pump activity4. Increased inward permeability to calcium
Rhythms Originating in SA NodeSINUS BRADYCARDIA• It is characterized by atrial and ventricular ratesof less than 60 beats/minutes.• It occur gradually or suddenly for a brief period.• It is usually a benign dysrhythmias and iscommon among general population• It is commonly seen in athletes and also beassociated with sleep
• Right and left Vagus nerve fibers of theparasympathetic nerve system plays animportant role in the rate of impulse formation,the speed of conduction and the strength ofcardiac contraction.• Stimulation of the Vagus nerve causes adecrease rate of firing of the SA node, slowedimpulse conduction of the AV node, anddecreased force of cardiac muscle contraction.
• Stimulation of the sympathetic nervesystem that supply the heart has essentiallythe opposite effect on the heart.
Valsalva maneuver• The Valsalva maneuver or Valsalvamanoeuvre is performed by moderately forcefulattempted exhalation against a closed airway,usually done by closing ones mouth andpinching ones nose shut.
• Variations of the maneuver can be used either inmedical examination as a test of cardiac functionand autonomic nervous control of the heart, or to"clear" the ears and sinuses (that is, to equalizepressure between them) when ambient pressurechanges, as in diving, hyperbaric oxygen therapy,or aviation.• The technique is named after Antonio MariaValsalva
The normal physiological responseconsists of 4 phases• Initial pressure rise: On application ofexpiratory force, pressure rises inside the chestforcing blood out of the pulmonary circulationinto the left atrium. This causes a mild rise instroke volume.
• Reduced venous return and compensation:Return of systemic blood to the heart is impededby the pressure inside the chest. The output of theheart is reduced and stroke volume falls. Thisoccurs from 5 to about 14 seconds in theillustration. The fall in stroke volume reflexivelycauses blood vessels to constrict with some rise inpressure (15 to 20 seconds).
• This compensation can be quite markedwith pressure returning to near or evenabove normal, but the cardiac output andblood flow to the body remains low. Duringthis time the pulse rate increases.
• Pressure release: The pressure on the chest isreleased, allowing the pulmonary vessels andthe aorta to re-expand causing a further initialslight fall in stroke volume (20 to 23 seconds)due to decreased left ventricular return andincreased aortic volume, respectively. Venousblood can once more enter the chest and theheart, cardiac output begins to increase.
• Return of cardiac output: Blood return tothe heart is enhanced by the effect of entryof blood which had been dammed back,causing a rapid increase in cardiac output(24 seconds on). The stroke volume usuallyrises above normal before returning to anormal level. With return of blood pressure,the pulse rate returns towards normal.
Sinus Bradycardia• Deviation from NSR- Rate < 60 bpm
Sinus Bradycardia• Etiology: SA node is depolarizing slowerthan normal, impulse is conducted normally(i.e. normal PR and QRS interval).
ManagementInj Atropine Sulphate is administered ifpresented with hypotension, restless, chestpain, other signs of hemodynamic changesDecrease the Vagal stimulationAvoid drugs which causes BradycardiaTranscutaneous pacingDopamineEpinephrineIsoproterenol
Sinus Tachycardia• It is characterized by an atrial and ventricularrate of 100 beats/minute or more.• Generally the upper limit of sinus tachycardiais 160 beats/ minute.
Sinus TachycardiaCauses• Increased Sympathetic Stimulation Exercise Emotions/ excitement Fever Fear Acute painAny condition that require a higherbasal metabolism
Causes……..• Hyper metabolic States• Blood Loss• Consumption of alcohol, caffeine and tobacco.• Drugs likeAtropineDopamineDobutamineNor epinephrineamphetamines
• It can be a short term compensatory responseto heart failure, anemia, hypovolemia, andhypotension.• HyperthyroidismCauses……..
Sinus Tachycardia• Deviation from NSR- Rate > 100 bpm
Sinus Tachycardia• Etiology: SA node is depolarizing fasterthan normal, impulse is conductednormally.• Remember: sinus tachycardia is a responseto physical or psychological stress, not aprimary arrhythmia.
Management• Treatment is directed at the cause• Digitalis• Beta-blockers• Diltiazem• Carotid Sinus Massage
Sinus Arrest/Sinus Pause• Sinus node automaticity is depressed• Impulses are not formed when expected• No P wave or no QRS complex is generated• Patient may feel palpitation from theincreased stroke volume that accompaniesthe next beet after the pause.
Etiology• Vagal Stimulation• Hypoxia• Myocardial ischemia• Injury to SA node• Carotid sinus sensitivity• MI• Drugs:- Digitalis, Beta-Blocker and Ca-Channel Blockers
ECG Characteristics• Rate- Normal unless sinus node fails toform impulse• Rhythm-Irregular• P_waves- present when SA Node Initiates• PR interval –normal if P waves present• QRS –present, absent when arrest
Management• Treatment is directed to the Cause• Discontinue/withheld offending drugs• Minimize Vagal Stimulation• Inj Atropine sulphate• Insertion of a permanent pacemaker
Sick Sinus Syndrome• The term sick sinus syndrome is used todescribe the rhythm in which there ismarked sinus bradycardia, sinus pause orperiods of sinus arrest alternating withparoxysms of rapid atrial arrhythmias.• The term brady- tachy syndrome iscommonly used to describe the samearrhythmias.
Causes• Inflammatory cardiac disease.• Cardiomyopathy• Sclerodegenerative process involving boththe SA and AV node• Drugsbeta-blockerscalcium-channel blockersdigitalis, amiodarone, and adenosine.
Etiologies of Sick Sinus SyndromeMore CommonSinus node fibrosisAtherosclerosis of theSA arteryCongenital heartdiseaseExcessive vagal toneDrugsLess CommonFamilial SSS (due tomutations in SCN5A)Infiltrative diseasesPericarditisLyme diseaseHypothyroidismRheumatic fever
ECG characteristics• Rate :varies from bradycardiac to tachycardiacrates depending on sinus node function andpresence of atrial tachy dysrhythmias• Rhythm: irregular• P waves : normal during sinus rhythm• PR interval : may be normal depend upon thestate of AV conduction• QRS complex: usually normal
Sinus bradycardia (rate of ~43 bpm) witha sinus pause
Abrupt termination of atrial flutter with variable AV block,followed by sinus arrest with a junctional escape beat.
Clinical manifestations• Patients are usually elderly and present withlightheadedness and/or syncope,• but it can also manifest as• angina,• dyspnea,• and palpitations.
Treatment• Ing.Atropine sulphate for brady arrhythmias• Atntiarrhyhmics like quinidine orprocainamide• Permanent pacemaker insertion
Atrial TachycardiaIt is rapid atrial rhythm at a rate of 120 to 250b/min. It is due to rapid firing of an ectopicfoci present in the atriaAtrial tachycardia frequently occurs inparoxysms.
Possible mechanisms of atrial Tachyarrhythmias.• Two groups of fundamentally differentmechanisms are responsible for producingTachy arrhythmias• 1- those mechanisms based on some form ofabnormal impulse formation• 2- based on a disorder of impulse conduction,leading to circulating excitation or reentry.
Pathophysiology• The spontaneous depolarization in the fibersin the center of the sinus node is normallythe fastest, and therefore this depolarizationbrings these fibers to a discharge beforeothers. Thus under normal conditions,automaticity of the dominant pacemaker inthe center of the sinus node suppress thesubsidiary pacemakers in the atria.
• Abnormal impulse formation may bedefined as the generation of impulses byfibers other than the dominant pacemakerfibers in the centre of the sinus noderegardless of whether the abnormalimpulse is generated spontaneously orinduced by foregoing normal or abnormalactivities.
• Normal impulse formation is the occurrenceof a spontaneous depolarization before theonset of an action potential, the so- calleddiastolic depolarization.• If depolarization occurs either duringrepolarization or under special conditionsdirectly after repolarization the termabnormal impulse formation may be used.
• There are some muscle fibers in the rightatrium close to the crista terminalis that have asome characteristics of purkinje fibers (ie.Relatively low resting potential and developsspontaneous depolarization under certainconditions)
ECG Characteristics• Rate- 140-250/min,• Rhythm- regular unless there is block• P-wave- differ in configuration• PR interval- may be shorter and difficult tomeasure• QRS- Usually normal
Signs and Symptoms• Palpitation• Light headedness• Angina• Syncope
Management• Sedation to terminate the rate• Carotid sinus massage• Cardioversion if severe symptoms occurs• Beta-blockers• Radiofrequency catheter ablation of theectopic focus
Atrial FlutterA rapid well-organized contraction of the atriumat a rate of 200-350 contractions per minutewhich is fired by ectopic foci present in theatria.Atrial flutter can be classified in to two typestype-1 which is the commonest one has anatrial rate of 240-340 beats/ minute
ECG Characteristics• Rate- Atrial 250 to 350b/minVentricular 150 to 200b/min• Rhythm- Atrial Rhythm is regularVentricular may be irregular• P waves- saw tooth appearance• QRS- usually normal• PR Interval not measurable
ECG Characteristics• Rate- ventricular rate 100 to200b/min• Rhythm- usually regular• P-waves present if S.A.Node firesmay be buried in QRS or T• PR Interval- not measurable• QRS- wide, bizarre and greaterthan 0.12sec
Management• Cardioversion• Defibrillation can be done when thepatient is pulseless• Inj Lidocaine bolus and drip asmaintenance dose• Antiarrhythmic like inj Amidaroneor inj MgSo4• Resuscitative measures to keptready
Ventricular Fibrillation• An erratic, disorganized firing ofimpulses from the ventricles.
Etiology• Myocardial Infarction• V-Tach• Drug toxicity• Electrocution• Drowning
ECG Characteristics• Rate- rapid, uncoordinated, ineffective• Rhythm- Chaotic, irregular• P waves- not seen• PR interval- none• QRS – no formed QRS complex
Management• Defibrillation• CPR must be performed• Anti-arrhythmic likeinj Lidocaineinj Procainmideinj MgSo4 most commonlyused• Beta-Blockers
Disorders of impulse Conduction• S.A. Block• First degree AV Block• Second Degree A.V.Block» Mobitz type I» Mobitz type II• Third Degree or Complete A.V Block• Bundle Branch Block» RBBB» LBBB
First Degree A.V.Block• It is defined as prolonged AVconduction time of supraventricularimpulses into the ventricles.
ECG Characteristics• Rate- usually normal• Rhythm- irregular unless 2:1conduction present• P waves- normal. Some p waves arenot conducted to the ventricle, butonly one at time fails.• PR Interval- gradually lengthens inconsecutive beats.• QRS- normal unless BBB
Management• Treatment depends on theconduction ratio, ventricular rate• If the ventricular rate slow giveinj Atropine Sulphate• Removal of precipitating factor• Temporary pacing can be done.
Type II Second degree A.V.Block• It is sudden failure of conduction ofan atrial impulse to the ventricleswithout progressive increase inconduction time.
ECG Characteristics• Rate- normal• Rhythm- irregular• P waves- usually regular andprecede QRS.Periodically a Pwave is not followed by aQRS• PR interval- constant unless thereis block• QRS- usually normal
ECG Characteristics• Rate- atrial normal, Ventricularrate is less that 45/min• Rhythm- Regular• P waves- independent• PR Interval- no consistent PRinterval• QRS- Normal If ventriclescontrolled by Junctionalpacemaker, may be wide
Management• Onset is sudden or associated withMI pacing can be done without delay• CPR should performed if the cardiacout put severly diminished
Ventricular Asystole• It refers to the absence of anyventricular rhythm; there is no QRScomplex, no pulse and no cardiacoutput.
Management• Cardio Pulmonary Resuscitation• Endotracheal Intubation immediately• Obtain IV Access• Confirm Asystole in more than one lead• Consider immediate TranscutaneousPacing• Epinephrine 1 mg IV push q3-5 minutes– Consider Vasopressin as alternative• Atropine 1 mg IV q3-5 minutes
The P wave is caused by atrialdepolarization. The P wave duration isnormally less than 0.12 sec. The P wave isusually smooth and positive.The QRS complex represents ventriculardepolarization. The normal QRS intervalrange is from 0.04 sec - 0.12 sec, measuredfrom the first deflection to the end of theQRS complexThe T wave due to ventricularrepolarization The wave is normallyrounded and positive.
• The PR interval is the beginning of the P wave tobeginning of QRS complex. It is normally 0.12 -0.20 seconds. (onset of atrial depolarization to onset ofventricular depolarization)• The QT interval begins at the onset of the QRScomplex and to the end of the T wave.• The ST Segment represents the period ofventricular muscle contraction beforerepolarization.
• The ECG below illustrates primary ST-T wave abnormalities (leadsI, II, aVR, V5, V6) in a patient with RBBB. ST-T waveabnormalities such as these may be related to ischemia, infarction,electrolyte abnormalities, medications, CNS disease, etc.
• In the above ECG the ST-T waves are "normal" forLBBB; i.e., they are secondary to the change in theventricular depolarization sequence.
Wolff-Parkinson-White Preexcitation• Early ventricular activation in region of the accessory AV pathway• Short PR interval (<0.12s)• Initial slurring of QRS complex (delta wave) representing early ventricularactivation through normal ventricular muscle in region of the accessorypathway• Prolonged QRS duration (usually >0.10s)• Secondary ST-T changes due to the altered ventricular activation sequence
The ectopic atrial rate is 150 bpm. Some of the ectopic P waves are easily seen and indicated by thearrows. Other P waves are burried in the T waves and not so easily identified. Atrial tachycardia with AVblock is often a sign of digitalis intoxication. 3:2 and 2:1 AV block is seen in this example.
Premature Atrial ContractionsWhen an irritable focus in the atriafires before the next sinus impulseis due