Some great new blog posts over at EMS 12 Lead

• Discordant ST-Segment Elevation in LBBB or Paced Rhythm
• The Six Step Method for 12-Lead ECG Interpretation
• "New" LBBB – What’s the big deal?
• Identifying AMI in the presence of LBBB

Relates well the the Tim Phalen lecture we had on 12 Lead EKGs.

Good Stuff….

Been a while since we did cardiology so I wanted to do a quick review on the normal deflections you should expect to find in each lead of an EKG

Limb Leads

Lead I – Looks across top of heart with positive electrode at left arm – so QRS complexes are upright but not that tall

Lead II – Follows normal electrical axis of heart, top right to bottom left . All complexes should be upright and tall.

Lead III – Looks from top left towards bottom left – at this angle P waves may be inverted but QRS should be upright (more than in lead I)

Lead aVR – Positive on right arm, so everything negatively deflected

Lead aVL – Positive on left arm – similar to Lead I but this lead looks down AND to the right so QRS are upright but very small

Lead aVF – Positive at left leg, looking at bottom of heart. Electricity is coming right at this lead so QRS should be upright and prominent.

 

Chest Leads

Leads V1-V6 – R wave starts very small and S wave is prominent. As the leads progress the R wave is more prominent and S wave is gone in V6. This is known as R wave progression.

  P Wave

P wave should be upright in Leads I and II as well as V3-V6

P wave always inverted in aVR

P wave usually upright in aVF and V3 but occasionally biphasic or flat

P wave is variable in leads III,  aVL, V1 and V2 (upright, inverted, biphasic)

Inverted P wave in II, III and aVF and upight in aVR is diagnostic for a Junctional or low ectopic atrial rythm.

Most people say that your best view of the P wave is in Lead II – others say V1. The truth is that every patient is different, find the best one on your patients EKG and study that one well.

 

See this page for some quick review and this page

Andy Rodriguez

First Degree Heart Block

• Not a true block
• Conduction delay at AV node
• All impulses are conducted to ventricles
• PRI will be >0.20 consistently across the strip

Second Degree Heart Block

• Intermittent
• Some get through and some don’t
• pathology can be in AV node or below in Bundle of His
• pathology is often blended with other blocks
• Mobitz Type I (Wenckebach)
• Impulses encounter progressive delays at the AV node until one impulse is blocked completely
• PRI starts getting progressively longer and then dropped QRS
• All conducted QRSs present are tight, <0.12 and preceded by a P wave
• Mobitz Type II
• Can be regular or irregular, depending on conduction ratio
• Usually a Brady rhythm
• More than one P wave for every QRS
• PRI constant on conducted beats can be >0.20
• QRS <0.12
• Conduction Ratios
• 2:1, 3:1, etc. two P waves for every conducted QRS

Third Degree Heart Block (Complete Heart Block)

• All impulses generated by Sinus node are being blocked by AV node
• Separate Sinus and Ventricular Pacemakers –
• Complete disassociation between P waves and QRSs
• Regular
• Rate depends on whether its junctional or ventricular
• P waves, normal and upright, more P waves than QRS
• PRI – no relationship between P waves and QRS , occasional superimposed on QRS
• QRS width depends on whether its junctional or ventricular

Heart blocks are best diagnosed using a 12 Lead EKG Machine. This and other used medical equipment can be found easily online.

Download Excel Version Here

UPDATED 6/15/09

Sinus Blocks, Pauses and Arrest

• In all cases, no P, QRS or T wave present – Impulse is blocked a SA node and Atria are never depolarized.
• Sinus Block – Always a multiple of underlying P-P interval. can be more than one missing complex
• Sinus Pause – Not a multiple of P-P interval. Shorter than three times the P-P
• Sinus Arrest – Same as pause but more than 2 missing complexes (consecutive)

Andy Rodriguez

Ventricular Rhythms

• Impulse is generated in the ventricles. Generally recognized by wide QRS complex, >0.12

Premature Ventricular Contraction (PVC)

• Regular – ectopics will interrupt
• Rate – depending on underlying rhythm
• No P wave before PVC
• Wide QRS >0.12
• 
• 
•  

Compensatory Pause

• Allows for heart pick up its rhythm again after a PVC, resumes normal rhythm as was before PVC
• 2x R-R
•  

Interpolated

• R-R stays the same and PVC is between normal R-R
•  

Types of PVCs

• Unifocal – One focus generating the extra beat, generates PVCs that look exactly the same
• Multifocal – Multiple foci generating extra impulses. generates PVCs that look different

R on T Phenomenon

• PVC hits during or end of T wave, can cause Vfib if hits just right
• 

PVC Couplets

• Two PVCs in a row
• May be unifocal or multifocal

PVCs in a run or Run of PVCs

• More than three PVCs in a row
• Also called a “run of vtach”

PVC Groupings

• 1:1 Ratio – Bigeminy (every other is a PVC)
• 2:1 Ratio – Trigeminy (every third is a PVC)
• 4:1 Ratio – Quadgeminy (every fourth is a PVC)

Ventricular Tachycardia

• Usually Regular – can be slightly irregular
• Rate of 150 – 250 (Less than 150 is slow VT, greater than 250 V flutter)
• No P waves
• PRI – None
• QRS- wide and bizarre >0.12
• 

Ventricular Fibrillation

• Multiple foci firing in an uncoordinated fashion
• Grossly irregular
• Wide QRS – Fibrillating
• No pulse
• Shockable Rhythm
• Most lethal rhythm
• 

Idioventricular Rhythm

• Regular rate at 20-40 BPM (above 40 -120 called an accelerated idioventricular rhythm)
• No P waves
• No PI
• QRS wide and bizarre
•  

Asystole

• Absence of any electrical activity

Andy Rodriguez

Impulse is generated somewhere near the AV node. Impulses can travel up or down causing absent or inverted P wave – sometimes after the QRS. QRS is normal and tight.

Premature Junctional Contraction (PJC)

• Irritable site in AV junction fires prematurely producing a single ectopic beat.
  • Regularity depends on underlying rhythm
  • Rate – same
  • P Wave: Inverted, can fall before, during or after QRS
  • PRI, if measurable, <.12
  • QRS <.12
  • 

Junctional Escape Rhythm

• Higher pacemaker sites fall and AV junction takes over, atria are depolarized via retrograde conduction. Ventricular conduction is normal.
  • Regular
  • Rate: 40-60
  • P Waves, inverted, during or after QRS
  • PRI – only if there is a P wave and before and will be <.12
  • QRS <.12
  • 

Accelerated Junctional Rhythm

• Irritable focus in the AV junction fires repeatedly at a rate faster than the SA node. Retrograde conduction to atria and conduction to ventricles is normal
• Regular
• Rate: 60-100
• P Wave: inverted, before or after QRS
• PRI – only if there is a P wave and before and will be <.12
• QRS <.12
•  

Junctional Tachycardia

• Irritable focus in the AV junction fires repeatedly at a rate faster than the SA node. Retrograde conduction to atria and conduction to ventricles is normal
• Regular
• Rate: 100-180
• P Wave: inverted, before or after QRS
• PRI – only if there is a P wave and before and will be <.12
• QRS <.12
• 

Supraventricular Tachycardia (SVT)

• Rapid, Regular, SV rhythm that is so fast that you cant see P waves. Normal QRS
• Rate >150
• 

Paroxysmal Supraventricular Tachycardia (PSVT)

• A short burst of SVT that occurs in a rhythm strip
•  

More on EKGs… Andy Rodriguez

Escape Mechanism – normal pacemaker slows down or fails and a lower pacing site assumes pacemaking responsibility.

Sympathetic – both Atria & ventricles
Parasympathic – Only Atria

Analyzing the rhythm

• Regularity – Rhythm
  • regular
  • irregular
  • pattern to irregularity
  • ectopic beats
• Rate
• P Waves
  • present
  • regular, one for every QRS
  • before QRS or after
  • deflection – normal and upright in lead II
  • all P waves look alike
  • are irregular P waves associated by ectopic beats
• PR Intervals (PRI)
• QRS Complex
  • equal duration
  • measurement
  • normal limits
  • all look alike?
  • are unusual QRS complexes associated with ectopic beats?

Sinus Rhythms

Normal Sinus Rhythm – Regular, 60-100 BPM, P waves normal and upright, one before every QRS, PRI 0.12-0.20 and QRS <0.12

Sinus Bradycardia - Regular, Rate <60 BPM, P waves normal and upright, one before every QRS, PRI 0.12-0.20 and QRS <0.12

Sinus Tachyardia - Regular, Rate >100 BPM (usually 100-160), P waves normal and upright, one before every QRS, PRI 0.12-0.20 and QRS <0.12

Sinus Arrhythmia – sinus node fires faster during inspiration and slower during expiration. rate is still normal, and still normal QRS –
Irregular, 60-100 BPM, P waves normal and upright, one before every QRS, PRI 0.12-0.20 and QRS <0.12

Atrial Rhythms

Wandering Pacemaker – pacemaker site wanders between SA node, atria and AV node. rate is usually normal and will conduct normally to ventricles
Slightly Irregular, 60-100 BPM, P wave morphology changes from beat to beat, one before every QRS, PRI 0.12-0.20 but may vary, and QRS <0.12

Premature Atrial Contraction (PAC) – irritable focus within atrium that fires prematurely and produces a single ectopic beat. impulses are conducted normally.
Usually regular (depending on underlying rhythm) except for PAC, 60-100 BPM, P wave changes – one that comes early looks different than normal sinus P waves, one before every QRS, PRI 0.12-0.20 but may be longer, and QRS <0.12

Atrial Tachycardia (or SVT)– Single atrial site fires repetitively at a very high rate. impulses conducted normally
Regular 150-250 BPM, P wave looks different than sinus p wave if visible at all, one before every QRS, PRI not measurable, QRS <0.12

Atrial Flutter -  single focus initiates rapid repetitive impulses, AV node protects ventricles by blocking conduction of some impulses. Atrial Rhythm- regular, several flutter waves (saw tooth)before each QRS (F waves), PRI unable to determine, atrial rate 250-350 bpm

Atrial Fibrillation – multiple foci initiate rapid repetitive impulses, AV node protects ventricles by blocking conduction of some impulses.
Grossly irregular, atrial rate >350 bpm, ventricular rate varies greatly, no discernable P waves, no PRI, QRS <.12

Steve Kanarian

Some cardiology review:

• Location of Heart: Retrosternal
• Point of maximal impulse, Left 5th intercostal, midclavicular line, above mitral valve as well.
• Pericardium contains approx 30cc of fluid
• CO= SV x HR
• Frank Starling Law – (use fluid challenge to increase CO, increase in volume = increase in stretch therefore increase CO)
• S1 – closing of mitral and tricuspid valves
• s2 – closing of pulmonic and aortic valves
• s3 – murmur, caused by ventricular filling, caused by left sided CHF
• s4 – sign of CHF
• Coronary Vessels come off base of aorta and come back via the coronary sinus
  • right coronary artery (RCA) (right atrium and ventricle)
  • left coronary artery (LCA) splits; (mostly left ventricle and atrium)
    • left anterior descending
    • circumflex coronary
• Preload; pressure in ventricle at diastole
• Afterload; pressure against which heart has to pump

Depolarization causes contraction.(Na+ rushes in) Repolarization is the refractory state. (K+ left in the cell)

Cardiac Physiology

(Bundle of Kent – Wolf Parkinson’s White –WPW)

EKG Lead Placement

• Bipolar (Limb) Leads – impulses traveling towards positive lead, upright wave, going towards negative lead, points down
• Augmented (Unipolar) Leads – Boosted Electrically)
• Precordial (Chest) Leads- V1-V6 (Septal 1,2, Anterior 3,4 Lateral 5,6 Inferior 2,3, aVF) SALI

Electrical Conductivity and the EKG

‘Monitoring’ leads are not diagnostic, 12 Lead EKG Machines are diagnostic quality

ECG Paper

• Speed (horizontal Boxes smallest= .04 sec, big box is .20 sec)
• Amplitude – Vertical box = 0.1mV height  (1mm)

Normal Electrocardiogram

• P-R Interval (PRI) – 0.12 – .20 sec (Prolonged PRI indicates Heart block)
• QRS – <0.12 sec – wider indicates rhythm below AV node
• QT interval – Q wave to repolarization – prolonged means heart is at risk for ventricular dysrythmias (poisoning, overdoses)

5 points to look for

• Rate
• Rhythm
• P waves
• PRI
• QRS