Electrocardiogram (ECG)

Rate

Normal rate is 60-100 bpm, with everything below or above termed bradycardia or tachycardia, respectively.

 

A few ways to count the rhythm:

Big blocks: 300, 150, 100, 75, 60, 50

 

60000/small boxes

Rhythm

Assess for sinus rhythm by measuring the interval between a number of R waves. Mark a paper at 3 peaks and slide the paper along to compare spacing.

Sinus rhythm is present there is a QRS after every P, P after every QRS and Narrow QRS complexes.

If sinus rhythm is not present, identify the arrhythmia.

 

ST segment

ST depression suggests myocardial ischemia, while ST elevation is representative of myocardial infarction. It is wise to assess it quickly in cases of clinical suspicion due to the potential urgency of what it could suggest.

 

The ST segment represents a period of relatively little electrical activity in the heart.

 

The QT interval, measured from the beginning of the Q wave to the end of the T wave, represents the duration of ventricular depolarization and repolarization.

 

Axis

While all information is relevant, the mean QRS axis is the most clinically important and is calaculated from the six limb leads.

 

Lead I, traveling from right to left, is defined as the 0^o axis, and from there all other leads are assigned a relative axis.

A normal axis is between -30 and +90.

 

A quick way to determine mean QRS axis is to observe which of the six limb leads has the most isoelectric-appearing complex. The mean axis is simply perpindicular to it. It could, however, be +90^o or -90^o perpendicular, so observing a perpindicular lead for whether or not it is positive will provide that answer.

 

Another quick way is to assess leads I and II. If the QRS is positive in both, there is likely no axis deviation.

 

Left axis deviation is more common. It suggests left anterior fascicular block, previous anterior/inferior MI, or potentially cardiac pacing. More uncommon is WPW.

 

Right axis deviation suggests RVH, left posterior fascicular block, or pulmonary embolus.

 

 

 

P Waves

The P wave is composed of the contractions of the left and right atria. The right atrium contracts slightly faster than the left. Both RA and LA contractions are positive in lead II, while the RA is positive and the LA negative in lead V1. This can shed some light on enlargements of each.

 

 

P wave abnormalities

• Absent P wave and irregular rythm suggests atrial fibrillation
• Saw tooth pattern of P waves depicts A flutter
  
• Two different P waves suggests ectopic focus that does/does not activate ventricle. Causes including anything that excites atria, including coffee.
• P mitrale: LAH- Prolonged P wave>120msec/3 small boxes,notching/"bipeak" P
  wave,Biphasic P wave in Lead V1 with negative deflection >1 small box
• P pulmonale: RAH- Peak P wave with amplitude >1 big box

PR Interval

The normal PR interval, measured from the beginning of the P wave to the onset of QRS, is 0.12-0.20 sec, or 3-5 small boxes. It is decreased in junctional rhythms and increased in first degree AV block.

 

Second and third degree heart block..

 

If PR interval is shortened, suspect left atrial hypertrophy or ectopic foci that take over pacing.

 

QRS Complexes

The normal QRS length, measured from the beginning to the end of the QRS complex, is <0.1 sec, or less than 2.5 small boxes.

Complexes greater than 0.12 seconds are usually due to interventricular conduction delay.

 

 

Assess for R wave progression throughout V1-6, morphology, QRS duration and sometimes amplitude. It is better to do the assessment by examining them by regional grouping to identify abnormalities.

• inferior: II,III,AVF (RCA)
• anterior: V1-4 (?)
• lateral: I, V5-6,aVL (circumflex)

 

Although each lead represents a unique view, they can be grouped together according to their representative area of the heart. This is particularly important when assessing the possibility of myocardial infarction.

• I, aVL, V3, V6 - lateral
• II, III, aVF - inferior
• aVr

 

Poor R wave progression can be caused by

• previous MI
• ideopathic
• PE
• LVH
• right ventricular overload
• ?copd

 

Morpohology - (>1small box for duration + >1/3 height or Rwave), most like indicates previous infarct.

 

Patterns of Heart block if QRS widened

• M wave on V1-2 and slurred ST segment on V5-6 with right block
• M wave on V5-6 if left block
  

 

Sometimes QRS complexes are shorter than 1 small box in amplitude. Causes include:

• low voltage
• athlete
• ischaemia
• pericarditis
• electrolyte abnormality

T waves

Ischemia and Infarction

Heart Blocks

 

 

Atrioventricular Heart Blocks

result of conduction disturbance -slowing or blocking - at the AV node.

 

Waveform

delayed PR intervals

 

 

 

 

First degree heart block

impulse delayed; prolonged PR interval >.2 s

often idiopathic

 

rate

usually normal

 

rhythm

usually regular

 

 

 

 

 

Second Degree Heart Block (Mobitz Type I)

PR interval increases intil aQRS complex is dropped

 

rate

atrial - usually within normal limits (60-100 bpm)

ventrical - slower

 

rhythm

artial - regular

ventricular- irregular

 

waveform

normal P waves, though not all followed by QRS

PR interval progressively longer until QRS is dropped

QRS normal

 

 

 

 

Second Degree Heart Block Type II

get a pacemaker- can progress to Type III

 

waveform

P waves

normal configuration

not all followed by QRS complexes due to

 

PR interval - may be normal

 

 

 

Third Degree Heart Block

atria and ventricles beat independently

 

rate

atria - unaffected - 60-100 bpm

ventricular - slower

 

rhythm

atria and ventricular - regular

 

waveform

P waves normal

PR interval - absent

QRS complex - normal if blocked at the AV node; wide if blocked in the bundle branch

 

 

 

Atrial Flutter & Fibrillation

Atrial Flutter

rate

atrial - 250-350

ventricular - variable; dependent on number of atrial beats conducted

 

rhythm

regular - if ratio of

 

 

 

 

 

Atrial Fibrillation

very common in elderly

rate

atrial -indiscernable 400-500 bpm

ventricular uncontrolled >100, controlled less <100

 

waveforms

P waves, and PR interval, are undefinable

wavy baseline

QRS complex less than 0.12s

 

rhythm

grossly irregularly irregular

 

Supraventricular Tachycardias

 

SVT aka narrow rhythmn tachycardias

• atrial tachycardia
• paroxysmal atrial tachycardia
• PAT/PSVT/SVT
• atrial flutter
• atrial fibrillation

SVT wave form configurations

P waves: arise from irritable foci above ventricle (not SA node)

may be notched or flattened

significance:

• decreases heart's ability to pump effectively, decreasing perfusion
• thrmobi formation can result in emboli
• can be insignificant if it is a perfusing rhythm; rarely progresses

 

Ventricular Tachycardia and Fibrillation

 

Ventricular Tachycardia

rate

atrial - none

ventricular 100-250 bpm

 

rhythm

regular

 

waveform

no P waves, no PR interval

QRS complexes normally wide, greater than 0.12s

 

 

 

 

 

Ventricular Fibrillation

rate

indeterminate

 

rhythm

irregular

 

waveform

nothing discernable

can discern coarse VF and fine VF

 

Hypertrophy

 

Left Ventricular Hypertrophy

In adults,

R in V6 and S in V1 adding to over 55 mm

 

 

 

 

 

Right Ventricular Hypertrophy

In adults,

R in V1 and S in V5 or V6 above 1.10 mV

 

In kids

In V1, upright T wave in days 3-6; q wave, tall R in V1 and deep S in V6

 

Bundle Branch Blocks

 

Right Bundle Branch Block

QRS widens because RV takes longer to depolarize (3 blocks or more)

An RSR' wave form is seen in lead V1.

 

 

Left Bundle Branch Block

Negative (QS wave) in V1, V2

An RSR' wave form is seen in V5 or V6.

An alternate way:

• count the S height in V1 or V2
• count the R height in V5 or V6
• >35 is LVH

Other

• pericarditis - Diffuse ST segment elevation
• right heart overload - get RSR' or rR' in V1, which suggests