ECG
20160408 Kaohsiung
Outlines Anatomy of the Conduction System Electrophysiology Principles ECG Arrhythmia
Anatomy of the Conducting System
Electrophysiology Principles !
Resting membrane potential " In the resting state, the interior of most cardiac cells is approximately -80 to -90 mV to extracellular electrode ! With the exception of the SA and AV node
!
Action potential ( ) " The ionic species responsible for the action potential varies among the cardiac tissues
Action potential of the His-Purkinje system
Electrocardiography (ECG)
ECG ECG Rhythm Rate P wave → PR interval → QRS complex → ST segment → T wave → U wave → QT interval
Rhythm Regular: sinoatrial (SA), AV junction, idioventricular Irregular: beats grouped in pairs, drop beats, totally irregular
Rate To count the number of cardiac cycles in 6 seconds and multiply by 10
P wave Depolarization of atria Upright in Leads I, II, aVF, V4-6 Inverted in Leads aVR Amplitude: not exceed 2-3 mm Contour: round Duration: no exceed 0.11 sec (0.01-0.12 sec)
PR interval SA node to ventricular muscle Duration: 0.12-0.21 sec To be shorter at faster rates, children, WPW syndrome and LGL syndrome To be longer due to conducting system disease, the effect of the drugs 0.52% of healthy airmen, >0.21 sec
QRS complex Depolarization of ventricles Duration Amplitude Q wave Electrical axis (in frontal lane) Transitional zone (in precordial leads) Intrinsicoid deflections General configuration
Q wave Wide Depth Location Clinical setting
Small narrow Q wave (1-2 mm): normal in I, aVL, aVF, V5-6 Deep Q: normal in aVR, occasionally in III, V1-2 Width < 0.03 sec Pseudo-Q wave
ST segment J (junction) point level relative to the baseline shape ST segment in limb leads: <1mm ST segment in chest leads: <2 mm
T wave Depolarization of ventricle Direction Shape Height in limb leads < 5mm in chest leads < 10mm
Normal upright: I, II, V3-6, (if QRS > 5mm, aVL, aVF) Inverted: aVR Variable: III, aVL, aVF, V1-2 slightly Round and asymmetric: Notching: normal children, pericarditis Sharply pointed symmetric T wave: MI, hyperkalemia
QT interval Total duration of ventricular systole Varies with heart rate, se and age QT shortened: digitalis, calcium excess, potassium intoxication QTc: male 0.40 sec, female 0.44 sec
QT prolongation: Congenital, ischemic heart disease, rheumatic fever, myocarditis, CVA, electrolyte disturbances, hypothermia Drugs: amiodarone, quinidine, procainamide, phenothazines, antihistamine, antibiotics
U wave Depolarization of papillary muscles or Purkinje system Same polarity as T wave Best seen in V3, in the condition of potassium deficiency Negative U wave: CAD
Atrial Enlargement Right atrial enlargement (RAE)
Left atrial enlargement (LAE)
P-pulmonale: P wave axis to +70 in chronic lung disease
width > 0.12 sec
P-congenitale
terminal negative in V1
Narrow pointed P waves in limbs and right chest leads
notched negative in III, and aVF intra-atrial conduction delay
Left Ventricular Hypertrophy(LVH) Deep S waves over the RV and taller R waves over the left S in V1 or V2 + R in V5 or V6 > 35 mm R in V5 or V6 >26 mm Strain Left axis deviation
Right Ventricular Hypertrophy R wave prominence in right precordial leads and deep S waves in left precordial leads R/S ratio >1.0, V4R is a more reliable than V1 Right axis deviation in limbs leads Prominent Q in II, III, aVF Strain in V1, V2, II, III, aVF
Combined Ventricular Hypertrophy
LVH in the chest leads with right axis deviation in the limbs leads LVH in left chest leads with prominent R wave in right chest leads (R/S >1 in V1)
Bundle-Branch Block Left bundle-branch block QS or rS in V1 Late intrinsicoid, no Q waves, monophonic R in V1 Monophonic R wave and no Q in lead I Right bundle-branch block Late intrinsicoid, M-shaped QRS; sometimes wide R or qR in V1 Early intrinsicoid, wide S wave in V6 Wide S wave in lead I
Sinus Node Dysfunction The bradyarrhythmias
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First-degree sinoatrial exit block " A prolonged
conduction time from the SA node to the surrounding atrial tissue
!
Second-degree sinoatrial exit block " The
intermittent failure of conduction of sinus impulses to the surrounding atrial tissue
!
Third-degree sinoatrial exit block " A lack
of atrial activity
Sick sinus syndrome !
Atrial tachyarrhythmias such as atrial fibrillation, atrial flutter, or atrial tachycardia may be accompanied by SA node dysfunction " Bradycardia-tachycardia !
syndrome
Failure of the sinus node to recover function following suppression of automaticity by atrial tachyarrhythmia Syncope/presyncope
AV conduction disturbances !
First-degree AV block " PR
interval > 0.20 s " Determined by atrial, AV nodal, and His-Purkinje activation !
Second-degree AV block " Some
atrial impulses fail to conduct to the ventricles
Mobitz type I (Wenckebach block) ! Mobitz type II !
!
Third-degree AV block " Periods
of two or more consecutively blocked P waves " Intermittent conduction
Ventricular rhythm
Junction rhythm
Premature complexes Atrial premature complexes (APCs) ! AV junctional complexes ! Ventricular premature complexes (VPCs) !
Atrial premature complexes (APC) Over 60% of normal adults on 24-h Holter monitoring ! Usually asymptomatic and benign ! Palpitation rare ! Asymptomatic APC: Treatment is not required ! Caused by alcohol, tobacco, adrenergic stimulants ! Trigger PSVTs ! ECG: the pause is less than fully compensatory !
AV junctional complexes AV junctional complexes are less common than either atrial or ventricular premature complexes ! more often associated with cardiac disease ! Can conduct in either direction ! Normal QRS without P wave ! Retrograde P waves (inverted in leads II, III, and aVF) ! Symptoms !
" Often
asymptomatic " Palpitations " Distressing pulsations in the neck !
Cannon a waves
Origin be in His bundle
Ventricular premature complexes Singly, bigeminy, trigeminy ! Pairs or couplets ! Ventricular tachycardia !
" â&#x2030;Ľ3
consecutive VPCs " rate >100 bpm " Sustained vs. nonsustained
Monomorphic ! Polymorphic !
Tachycardias Sinus tachycardia ! Atrial fibrillation ! Atrial flutter ! Paroxysmal supraventricular tachycardia ! AV nodal reentrant tachycardia ! AV reentrant tachycardia ! Sinus node reentry and other atrial tachycardias ! Preexcitation syndrome !
Atrial Fibrillation
Atrial flutter Atrial rate between 250 and 350 bpm ! Regular sawtooth-like atrial activity !
Mechanism of AV nodal reentrant tachycardia
Multifocal atrial tachycardia
Ventricular Tachycardia ! ! ! !
Wide QRS Rate > 100bpm Quite regular Paroxysmal VT is usually initiated by s VPC
Torsades de pointes (TDP) Polymorphic QRS ! Change in amplitude and cycle length ! QT prolongation !
Accelerated idioventricular rhythm
Slow VT ! Rate: 60-120 bpm ! Transient duration ! Rare hemodynamic compromise Etiology: !
" AMI
with reperfusion " Following cardiac operation " Cardiomyopathy, rheumatic fever, digitalis intoxication " Some with no evidence of heart disease
Ventricular Fibrillation