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● Lead I + lead III = Lead II (Einthoven’s Law) ○ Lead I LA → RA ○ Lead II LL→ RA ○ Lead III LL → LA
● Kirchoff’s Law –The sum of the potentials of AVR + AVL + AVF = 0
● NORMAL ○ P wave
■ Amplitude normally 0.5 to 2.5 mm (2.5 squares) (in limb leads)
■ Duration not over 110 msec (3 squares) (in limb leads) ■ In sinus rhythms, P wave is upright in Lead II and inverted in
aVR. If not, SA node is not pacemaker ■ Normal axis (frontal plane) is 0° to +90 °, usually +30 to +60
● Left axis 0 to 30 ° ● Right axis beyond +75 °
○ PR interval ■ Normal value in adults is 0.12 sec to 0.20 sec (ventricular preexcitation < 35 squares < 1st degree AV
block) ○ QRS
■ 60100ish ms (1.52.5 squares) ○ ST segment
■ Usually isoelectric, but may normally deviate between –0.5 and +1.0 mm from baseline in standard and unipolar extremity leads
■ Upward displacement of 2 or 3 mm may be normal particularly in right precordial leads ○ T wave 10% of amplitude of QRS is normal. ○ U wave
■ Polarity usually same as T wave ■ Most prominent in lead V3 ■ Maximum amplitude should not exceed 1 mm
● Alterations in automaticity of the SA node
○ Sinus tachycardia sinus rhythm > 100 beats/min
○ Sinus bradycardia sinus rhythm < 60 beats/min ○ Sinus arrhythmia increased sinus rate with inspiration.
■ withdrawal of parasympathetic tone during inspiration ○ Sinus arrest pause. SA node fails to fire.
■ can be caused by increased parasympathetics, hypersensitive carotid sinus, damage to SA node, digitalis ● Irregular Rhythms
○ Wandering Pacemaker pacemaker activity wanders from SA node to nearby atrial automaticity foci
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■ P’ shape varies ■ Atrial rate <100 (if >100 then becomes multifocal atrial tachycardia) ■ Irregular ventricular rhythm
○ Multifocal Atrial Tachycardia Chaotic Atrial Rhythm ■ P’ wave shape varies (Three or more ectopic Pwaves with different configurations/morphologies because P
waves come from different areas in the atrium.) ■ Isoelectric line between PP intervals ■ Frequent occurrence of varying PR intervals ■ Atrial rate >100 (100250 bpm) ■ Irregular ventricular rhythm ■ Seen in COPD
○ Atrial Fibrillation
■ Irregular rhythm and irregular ventricular rhythm ■ Chaotic atrial spikes
● Escape beat an automaticity focus transiently escapes overdrive suppression to emit one beat (A beat originating from a site other than the SA node). Long pause followed by escape beat (versus premature beat where there is no pause before)
● Escape Rhythm an automaticity focus escapes overdrive suppression to pace at its inherent rate (another normal pacemaker takes over) → a sequence of similar ectopic beats (many ectopic beats). When SA node pacemaker activity is impaired
○ Atrial escape rhythm ⇒ 6080/min
■ P’ waves are not identical to previous P waves which are from the SA node. (The same is for the escape
beat) ○ Junctional escape rhythm ⇒ 4060/min
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■ Conducts mainly to ventricles → series of lone QRS complexes. ■ Retrograde atrial depolarization leads to an inverted P’
● can be immediately before the QRS ● can be buried in the QRS ● can be after the QRS
○ Ventricular escape rhythm ⇒ 2040/min
■ large ventricular complexes ■ can be so slow that it causes StokesAdams Syndrome where not enough blood reaches the brain.
● Premature Beats ⇒ irritable focus spontaneously fires a single stimulus ○ Premature atrial beat ⇒ early P’ wave which can be hidden in the T wave with normal QRS following.
■ P’ can depolarize the ventricles leading to a wide QRS in the PAC beat only. ■ If not conducted, lone P wave with no QRS following. ■ Irritated by (same for premature junctional beat) epi, increased SNS stimulation, caffeine, amphetamines,
cocaine, other beta1 stimulants, excess digitalis, toxins, etoh (sometimes), hyperthyroid, stretch ○ Premature junctional beat ⇒ premature irritable stimulation from AV junction which depolarizes the ventricles and
sometimes in a retrograde fashion, will depolarize the atria.
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■ P’ wave can be before, during or after the QRS. ■ Upper AV Junctional Rhythm
● AV node not pacemaker. ● Retrograde/inverted P waves precede the QRS complexes by short PR intervals (start pacemaker
near AV node → travels faster because shorter distance) in leads II, III, and aVF ■ Middle AV Junctional Rhythm
● P waves cannot be identified since they are buried in the QRS complexes. Atrial fibrillation is ruled out since the base line shows no oscillations.
■ Lower AV Junctional Rhythm ● Retrograde P waves follow QRS complexes. They are best seen in leads II, III, and aVF ● Atria depolarized AFTER the ventricles depolarize.
○ Premature ventricular beat ⇒ irritate the ventricles
■ Wide and tall QRS with opposite polarity of the normal QRS ■ Only depolarizes the ventricles, not the SA node. ■ Irritated by airway obstruction, hypoxia, reduced CO, low potassium, mitral valve prolapse, stretch,
myocarditis ○ Ventricular Parastole ⇒ from an entrance block but not irritable PVC’s coupled to long series of normal cycles ○ Multifocal PVCs ⇒ each focus is own unique identifiable PVC ○ R on T ⇒ PVC falls on a T wave/falls on a vulnerable period and starts shit
■ from hypoxia and low serum potassium. ● Tachyarrhythmias ⇒ rapid ventricular rhythms originating in a very irritable automaticity foci
○ Paroxysmal (sudden) tachycardia ⇒ 150250 (sinus tachycardia is not sudden like paroxysmal) ■ Paroxysmal Atrial Tachycardia (PAT)
● rapid rate, spike P’ waves ● 2:1 ratio P’:QRS ● (suspect digitalis excess or toxicity digitalis can inhibit the AV node)
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● PAT with AV block → more than one P’ wave for every QRS response
■ Paroxysmal Junctional Tachycardia (PJT) sudden rapid pacing of a very irritable automaticity foci in the
AV junction ● inverted P’ before, during, or after the QRS can depolarize the atria in a retrograde fashion from
below ● Wide QRS from depolarizing left before right
■ Junctional Tachycardia → AV nodal reentry tachycardia
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● continuous reentry circuit → rapidly paces the atria and ventricles. Each pacing stimulus records in an origin near the coronary sinus.
■ Supraventricular tachycardia → irritable automaticity foci that produce both paroxysmal atrial and junctional tachycardia (above the ventricles)
■ Paroxysmal Ventricular Tachycardia → resembles a series of PVCs
● SA node still paces atria → independent pacing of the atria and ventricles (AV dissociation) ● Indicates coronary insufficiency leading to poor O2 to the heart.
● Distinguishing wide QRS insufficiency complex SVT from VTach.
SVT VTach
Pt with coronary disease or infarction uncommon very common
QRS width (duration) <0.14s >0.14s
AV dissociation showing captures or fusions
rare yes
Axis extreme RAD rare yes
● ■ Torsades de Pointes (250350)
● caused by low potassium, meds that block the K+ channels, congenital abnormalities,
long/lengthened QT segment. ● Possibly from two irritable foci in different ventricular areas.
○ Flutter ⇒ 250350 ■ Atrial flutter sawtooth shape
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● Originates in the atrial automaticity focus
■ Ventricular Flutter
● single ventricular automaticity focus ● Sine waves of similar amplitude ● Tends to go to VFib.
○ Fibrillation ⇒ 350450 (multiple foci discharge rapidly) ■ atrial fibrillation
● many irritable parasystolic atrial foci ● causes many irregular spokes on the EKG ● No identifiable P or P’ waves with irregular QRS response.
■ Ventricular Fibrillation
● Many irritable parasystolic ventricular automaticity foci pacing rapidly (entrance block)
■ WolffParkinsonWhite Syndrome
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● Delta wave = area of preexcitation ● Can have paroxysmal tachycardia
○ rapid conduction SVT (atrial flutter and afib) can be rapidly conducted through the accessory pathway
○ some bundles have automaticity foci that can initial paroxysmal tachycardia ○ Reentry ventricular depolarization may immediately restimulate the atria in a
retrograde fashion via the accessory pathway causing a theoretical circus reentry loop ■ LownGanongLevine Syndrome (LGL)
● AV node is bypassed by an extension of the anterior internodal tract (James Bundle) which
conducts atrial depolarizations directly to the Bundle of His without delay ● No significant PR interval delay ● P waves are adjacent to the QRS’s on EKG.
● Sinus Block ○ SA node may temporarily fail to pace for at least one cycle then resumes pacing ○ The pause can induce an escape beat from an automaticity foci ○ Sick Sinus Syndrome
■ seen in the elderly with heart disease ■ Marked sinus bradycardia without normal escape mechanisms or atrial and junctional foci ■ can develop bradycardiatachycardia syndrome ⇒ intermittent episodes of SVT (a flutter or afib)
○ AV Block ■ First Degree AV block
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● lengthened PR interval > 0.2 s (1 large square) ● No wide QRS
■ Second degree AV block ● Wenckebach → lengthening of PR interval until QRS is dropped.
● Mobitz 2 → 1 normal cycle preceded by a series of paced P waves that fail to conduct through the
AV node
■ Third degree AV block
● block of the conduction of atrial stimuli to ventricles. ● Atria and ventricles pace at different rates.
● Bundle Branch Block/Intraventricular Conduction Delay ○ block of one bundle branch which produces a delay of depolarization of the ventricle it supplies. ○ Wide QRS with rabbit ears (>0.12s) (3 squares or more in any lead) RSR’ ○ RBBB rabbit ears in V1, V2
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● Deep and round Swaves in I, aVL and V46 ● Secondary ST, Twave change in V13 ● abnormal depolarization and repolarization ● Complete RBBB with RVH > 15 mm. Can Dx only with RBBB.
● LBBB rabbit ears in V5, V6
○ Absence of septal qwaves in V46 (small q from septal activation not seen) ○ RSR’ or “M” pattern of QRS in I, aVL and V46 ○ Secondary ST, Twave change in I, aVL and V46 ○ Septal activation in opposite direction (R→ L)
● If RSR’ of normal QRS duration ⇒ incomplete BBB ● Intermittent mobitz occasional dropped QRS due to permanent BBB with intermittent BBB of other side.
● Hemiblock
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○ Anterior Hemiblock
■ LAD ⇒ usually associated with an MI (or other heart dz) ■ Normal or slightly widened QRS (0.100.12s) ■ Q1S3 ⇒ Q in I or wise/deep S in III) ■ Left Anterior block
● Mean and terminal QRS vectors are directed to the left of 30° in frontal plane ● Initial 0.02second QRS vector
○ Directed right and inferiorly and produces a small 0.02second Qwave in Lead I and AVL
○ Small 0.02second Rwave in Leads II, III and AVF ● Other causes of abnormal left axis deviation are ruled out i.e., inferior wall myocardial infarction
○ Anterior hemiblock with RBBB ■ RBBB mean QRS vector is within normal range or shows minimal RAD ■ RBBB + LAD = anterior hemiblock
○ Posterior hemiblock ■ RAD (usually associated with an MI) ■ normal or slightly widened QRS ■ S1Q3 Wide S in I and Q in III ■ Posterior block
● This condition is very difficult to diagnose right ventricular enlargement and lateral infarctions ● Mean and terminal QRS vectors in frontal plane show right axis deviation ● Initial 0.02second QRS vector
○ Directed slightly leftward and superiorly and produces a small 0.02second Rwave in Lead I and AVL (r/o anterolateral infarction)
○ Small 0.02second Qwave in Leads II, III and AVF ○ Bifascicular block
■ RBBB + anterior hemiblock ■ RBBB + posterior hemiblock
○ Intermittent block ■ continuous EKG pattern with intermittent wide QRS characteristic of intermittent BBB or with intermittent
changes of QRS axis. ○ Incomplete Trifascicular Block
■ Firstdegree AV block plus a right bundle branch block plus either a left anterior hemiblock or posterior hemiblock
● Axis direction of depolarization as it passes through the heart
○ origin of mean QRS vector is the AV node = tail of the vector. 090 is normal
○ Mean QRS vector will point toward hypertrophy and away from infarct
○ V1, V2 = rightward rotation ○ V5, V6 = leftward rotation
● Hypertrophy
○ Diphasic wave = atrial enlargement ○ Right atrial enlargement initial large deflection in V1. Tall
P wave
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■ if height > 2.5mm in II and >0.12s, suspect right atrial enlargement ■ pointed P wave greater than 2.5 mm, which is best seen in leads perpendicular to the heart bottom wall (II,
III, aVF) and chest leads V1 and V2 ○ Left atrial enlargement large terminal deflection in V1. Long P wave
● P wave is a prolonged and biphasic (bifid). It is best seen in leads I, II and aVL and sometimes possibly in
leads V5 and V6. (http://www.healthtutor.com/pmitraleecg.html ) ● Right ventricular hypertrophy
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○ Large R wave in V1, S wave is much smaller ○ The large R wave in V1 progressively becomes smaller in V2, V3, V4 ○ RVH causes RAD + rightward shift.
● Left ventricular hypertrophy
○ QRS complexes are exaggerated in amplitude eps. in chest leads. ○ Very tall R waves in V5 ○ Height/depth of S in V1 + height of R in V5 > 35 mm ⇒ LVH.
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○ Can see an asymmetrical inverted T wave (ideal leads V5/V6) ○ ventricular strain ○ V1 provides the most information regarding hypertrophy diphasic waves, R wave in V1, S wave in V1, R
wave in V5 ○ Accompanied by
■ left atrial abnormality ● >0.11s
■ Left axis deviation 030 ■ ST segment T wave changes → left ventricular strain pattern (systolic overload)
○ Extremity leads ■ Amplitude of Rwave in Lead I and/or AVL > 15 mm ■ Amplitude of Rwave in AVF > 21 mm ■ Sum of Rwave in Lead I plus Swave in ■ Lead III > 25 mm
○ Precordial leads ■ SV1 + RV5 or SV1 + RV6 > 35 mm ■ Rwave in V5 or V6 > 26 mm ■ Rwave in V6 taller than Rwave in Lead V5
● Infarction ○ Ischemia reduced blood supply
■ characterized by symmetric inverted T waves ■ Leads V2V6 is pathological ■ Marked T wave inversion in leads V2, V3 is Wellen’s Syndrome ⇒ Stenosis of anterior descending
artery. ○ Injury acute or recent
■ if no Q waves, can be nonQ wave infarction ■ ST elevation is infarct. Depression in reciprocal changes.
○ Pericarditis
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■ ST segment is elevated (diffuse) and usually flat or concave (middle sags down). ■ Entire T wave may be elevated off baseline
○ Subendocardial infarction
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○ Necrosis dead tissue
■ Q wave indicates necrosis → can Dx infarction ■ Insignificant Q waves < 0.04s (1mm) ■ Significant Q waves > 0.04s (or ⅓ QRS amplitude old criterion)
○ Anterior Infarct
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■ elevated ST segments and Q waves in V1, V2, V3, V4 ⇒ anterior descending of left coronary
artery ○ Posterior Infarct
■ Mirror image of anterior infarct ■ ST depression in V1, V2 ■ Large R waves, maybe Q in V6
○ Lateral infarct
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■ I, AVL Q waves ■ Circumflex left coronary artery
○ Inferior Infarct
■ II, III, AVF Q waves ■ right/left coronary artery
○ Cannot Dx infarction with LBBB
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● hyperkalemia
○ wide, flat P ○ peaked T ○ wide QRS
● Hypokalemia
○ T/U wave fusion. ○ Flat T wave ○ Prominent U wave
● Hypercalcemia
○ short QT interval
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● Hypocalcemia
○ prolonged QT interval
● Digitalis
○ positive inotrope Improve contractility of the failing heart (mechanical effect) ○ Prolong the refractory period of the AV node in patients with supraventricular arrhythmias (electrical effect) ○ inhibits the cell membrane sodiumpotassium ATPase pump ○ Therapeutic use for treating Atrial fibrillation ○ Salvador Dali’s mustache ○ Toxicity Sinus bradycardia, AV block, VTach secondary to ectopic beats
● Quinidine
○ Class IA antiarrhythmic (blocks Na and K channels) ○ retards and repolarizes ○ Long QT interval → can lead to Torsades ○ Wide, notched P ○ Wide QRS ○ depression ST ○ U wave