ECG Strip Interpretation

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Normal PR segment length

0.12 - 0.2 sec
3 - 5 small boxes

Normal QRS interval

0.06 - 0.1 sec
1 - 3 small boxes

Normal P amplitude & duration

< 0.12 sec (3 small boxes)
< 0.25 mV (2.5 small boxes)

causes of arrhythmias

HISDEBS: hypoxia, ischemia/irritability, SNS, drugs, electrolytes, bradycardia, stretch (hypertrophy/enlargement)

symptoms of arrhythmias

none, "palpitations," light-headedness, syncope, angina, HF, sudden death

Arrhythmias - 4 quick questions

1. Normal P waves?
2. Wide QRS? (> 0.12 sec indicates pacemaker below Bundle of His)
3. One P for every QRS?
4. Normal rate & rhythym?

Sinus arrhythmia

Appearance is ALMOST NORMAL:
Respiratory - Circulatory interaction
Rate INCREASES with INSPIRATION (IN=IN)

Sinus arrest - criteria

Rate: Regular or Bradycardia
P wave: Normal
QRS: Normal
Conduction: Normal
Rhythm: Irregular: length of pause ≠ multiple of normal rate (random)

Junctional Escape Beat/Rhythym - criteria

Rate: Bradycardia
P wave: Absent or Inverted P; if present, may occur during or after the QRS
QRS: Normal
Conduction: Escape beat: P-R interval < 0.12 seconds (if P present)
Rhythm: Irregular when it occurs (late)
If occurs 3 or more times in a row, is considered junctional escape rhythm

Sinus exit block - criteria

Rate: Regular or Bradycardia
P wave: Normal
QRS: Normal
Conduction: Normal
Rhythm:
Irregular: length of pause = multiple of normal rate
(Signal blocked leaving SA node; block is exactly equal to multiple of rate - one or more impulses "missed")

PACs (premature atrial contractions/atrial premature beats) - criteria

Rate: Regular underlying rate
P wave:
Abnormal - they originate from an ectopic pacemaker
QRS: Normal
Conduction:
Normal (except for PACs)
Rhythm:
Irregular when PACs occur (early)

PJCs (Premature Junctional Contractions)
AKA: Junctional Premature Beats

Rate: Regular underlying rate
P wave:
Absent or Inverted (like junctional escape)
QRS: Normal
Conduction:
PJC: P-R interval < 0.12 seconds (if P waves are present)
Rhythm:
Irregular when PJCs occur (early)

PSVT (Paroxysmal Supraventricular Tachycardia) AKA: AV nodal Re-entrant Tachycardia

Rate: Tachycardia (usually 150 - 200)
P wave: Absent or Inverted (like junctional escape)
QRS: Normal (may be wide, pseudo R')
Conduction: P-R interval < 0.12 seconds (if P)
Rhythm: Regular (abrupt onset and termination)
Carotid massage: slows or terminates

Atrial flutter

Rate:Atrial 250-350
Ventricular: 100 -175
P: Irregular or absent, often "saw tooth"
QRS: Normal
Conduction: AV Block (2:1 > 3:1, 4:1)
Rhythm: Regular (usually)
- Often underlying cardiac disease
Carotid massage: increases block

Atrial fibrillation

Rate: Atrial 400-650;
Ventricular usually 120 - 180
P wave: Not present; often wavy baseline
QRS: Normal
Conduction: Variable AV conduction
Rhythm: Irregularly Irregular
- chaotic, unpredictable depolarizations w/i atrium, no atrial kick
- CAD, HTN, COPD, etc.
Carotid massage: may slow ventricular rate

MAT (Multifocal Atrial Tachycardia):

Rate: Atrial varies, Ventricular 100-200
P wave: ≥ 3 different 'P' waves
QRS: Normal
Conduction: AV conduction, P-R intervals vary
Rhythm: Irregularly irregular
Carotid massage: no effect
Etiology: longstanding COPD, etc.

PAT (Paroxysmal (episodic) Atrial Tachycardia)

Rate: 100 - 200; Ventricular 1:1 (or 2:1, 3:1, 4:1)
P wave: Usually present, abnormal
QRS: Normal
Conduction: P-R interval varies (dt ectopic sites)
Rhythm: Regular (warm up &/or cool down)
Carotid massage: no effect, or only mild slowing

bigeminy?

1:1 ratio of normal:PVC

trigeminy?

2:1 ratio of normal:PVC

PVCs (Premature Ventricular Contractions)

Rate: Regular underlying rate (usually)
P wave: Absent (or abnormal) in PVC
QRS: PVC: wide > 0.12 seconds; shape is bizarre; T wave inversion
Conduction: Normal before & after PVC
Rhythm: Irregular; may occur in singles, couplets or triplets

Reasons to worry about PVCs?

- Frequency increasing
- Runs of 3 or more consecutively
- Multiple PVC foci
- R-on-T Phenomenon
- PVC in acute MI

Multiple PVC foci

Beats 1 and 4 are sinus in origin. The other three beats are PVCs. The PVCs differ from each other in shape (multiform), and two occur in a row.

PVC - R on T

A PVC falls on the T wave of the second sinus beat, initiating a run of ventricular tachycardia.

Ventricular tachycardia

Rate: 120 - 200 usually
P wave: Usually absent (unrelated to the QRS)
QRS: Wide & bizarre shape (PVCs)
Conduction: No correlation between 'P' if present and QRS
Rhythm: Regular or Irregular
* Cannon A waves may be present
Carotid massage: no effect

Ventricular Fibrillation

Rate: Not attainable
P wave: Obscured by ventricular waves
QRS: No true QRS
Conduction: Chaotic electrical activity
Rhythm: Irregularly Irregular

Torsades de Pointes

Rate: 120 - 200 usually
P wave: Obscured by ventricular waves
QRS: Wide QRS - "Twisting of the Points"
Conduction: Ventricular only
Rhythm: Slightly irregular

1º AV block

Rate: Normal (usually)
P wave: Normal
QRS: Normal
Conduction: P-R interval is > 0.2 seconds (delay)
Rhythm: Regular

2º AV Block - Wenckebach/Mobitz Type I

Rate: Normal or Bradycardia
P wave: Normal & constant P-P interval
QRS: Normal
Conduction: P-R interval is progressively longer until P wave is blocked; the cycle begins again
Rhythm: Irregular

2º AV Block - Mobitz Type II

Rate: Bradycardia
P wave: Normal & constant P-P interval
QRS: Normal or widened (usually associated with a bundle branch block)
Conduction:
P-R interval normal or prolonged (constant); some P waves are not conducted to ventricles (varies)

3º AV Block

Rate: Atrial 60-100; Ventricular 30-45
P wave: Normal with constant P-P interval ("marching through")
QRS: Usually widened (depends on location of escape pacemaker)
Conduction: Atrial & Ventricular activities are unrelated (complete block)
Rhythm: Irregular

Bundle branch blocks - general criteria

Due to changes related to the block, cannot say there is hypertrophy - BBB will make it look like hypertrophy

Rate: Regular or Bradycardia
P wave: Normal usually
QRS: Wide > 0.12 seconds
Conduction: Block occurs in the right or left bundle branches (or both)
Rhythm: Regular usually

Right bundle branch block (RBBB)

Right ventricular depolarization is delayed
Criteria:
- QRS complex > 0.12 seconds
- RSR′ in V1 and V2 (rabbit ears) with ST segment depression and T wave inversion
- Reciprocal changes in V5, V6, I, and aVL.

Left bundle branch block (LBBB)

LV depolarization is delayed
Criteria:
- Wide QRS > 0.12
- Broad (+/- notched) R waves, ST depression & T-wave inversion in I, aVL, V5, V6
- Broad S waves in V1, V2
- Left axis deviation may be present

Ischemic signs

- ST elevation or ST depression:
> 1mm related to baseline (0.08 s (2 boxes) after QRS)
- Also symmetric T-wave inversion in multiple precordial leads

Other causes of ST elevation

evolving transmural MI, Prinzmetal's angina, J point elevation, acute pericarditis, acute myocarditis, hyperkalemia, PE, Brugada syndrome, hypothermia

RBBB - underlying

May be otherwise normal (sometimes in athletes)

LBBB - underlying

Usually underlying cardiac disease

Wolff-Parkinson-White Syndrome (WPW)

- Bypass pathway (bundle of Kent) between atria & ventricles
- No pause at AV node - short PR interval
- Delta Wave: Slurred initial upstroke of R
Short PR interval < 0.12 seconds
Wide QRS > 0.1 second with delta wave

WPW risks

- PSVT dt reentrant pathway present; may be narrow QRS if via AV node & back up Kent, or wide (& hard to distinguish from V tach) if via Kent & back up AV node
- a fib - Kent acts as free conduit for chaotic atrial activity; may lead to V fib

Hyperkalemia

- Evolution of (1) peaked T waves, (2) PR prolongation & P wave flattening, & (3) QRS widening.
- Ultimately, the QRS complexes and T waves merge to form a sine wave, and ventricular fibrillation may develop.

Hypokalemia

- ST segment depression
- Flattening (or inversion) of the T wave
- Appearance of a U wave.

Hypercalcemia

shortened QT

Hypocalcemia

Prolonged QT
- risk of R on T leading to Torsades de Points

causes of long QT

- Medications: many antiarrhythmics, tricyclic antidepressants, quinolone antibiotics, etc.
- hypocalcemia
- Inherited disorder: Long QT Syndromes

Digitalis/Digoxin - indications

- Increase contractility
- Slows AV junction conduction
- Used to tx HF

Digitalis effect - therapeutic levels

Asymmetric ST depression, flat/inverted T-wave

Digitalis toxicity

- enhances automaticity --> tachyarrhythmias
- slowed AV conduction --> AV blocks
- PAT with block MC

pericarditis

DIFFUSE flat or concave ST elevation
- A large effusion can cause low voltage and electrical alternans.

pericardial effusion

1) low voltage - diffuse smaller waves
2) electrical alternans - axis changes w/ each beat; large QRS then small QRS

COPD

- Low voltage,
- Right axis deviation (RVH),
- poor R wave progression
- P pulmonale (right atrial enlargement;
tall P >2.5 in II) & abnormal P in V1) - "barrel chest" - increase AP diameter

Acute pulmonary embolism

Signs may include:
- RVH, RBBB (blood not getting through dt clot)
- Arrhythmias (s. tach & a fib MC)
- S1Q3: large S in lead I, deep Q wave ONLY in lead III (if deep Q in several, then infarct)

Brugada syndrome

structurally normal hearts
- autosomal dominant, M > W
- Resembles RBBB; ST elevation & RSR' in leads V1, V2, and V3.
- can cause fast polymorphic V tach (looks like torsades de pointes).
- ICD required (b-blockers no help)

Common in athletes

- sinus bradycardia as low as <30 bpm
- ST elevation in precordial w/ T flattening or inversion.
- LVH, sometimes RVH criteria
- Incomplete RBBB
- 1º or Wenckebach AV block.
- Arrhythmias (junctional, wandering atrial pacemaker)

Hypothermia

Osborne waves (ST elevation- abrupt ascent at J point & sudden plunge back to baseline) prolonged intervals, sinus bradycardia, slow atrial fibrillation. Beware of muscle tremor artifact.

CNS disease

Diffuse T wave inversion, with T waves typically wide and deep; U waves.

Indications for stress test

- eval CP/ro CAD
- eval >40 w/ risk factors for CAD
- assess pt response to interventions
- ?eval asx adults who want to start vigorous exercise (lots of false +)

criteria for selection of pts for stress test

- sx classic, atypical, or not at all angina-like?
- established CAD?
- functional tolerance to exercise?

stress test - contraindications

- angina at rest
- uncontrolled HF
- acute systemic illness
- severe aortic stenosis
- hypertrophic cardiomyopathy (sudden death)
- ability to walk/exercise
- caution if systolic > 200 or diastolic > 120; risk of hemorrhagic stroke!

normal physiological response to stress test

- incr SNS
- incr CO
- incr skeletal mm perfusion
- incr O2 extraction
- decr PVR
- incr systolic BP

stress test - pt preparation

- DC meds which may interfere (b-blockers, CCBs, digoxin, nitrates)
- no food, smoking, drink 2-4 hrs before
- pretest EKG
- pretest BP

stress test - finished when?

1) pt cannot tolerate dt compliance or sx
2) 90% of max HR reached
3) Significant EKG changes

stress test - positive when?

Horizontal or down-sloping ST depression (> 1mm & > 0.08 sec); earlier occurrence in test, more significant;
or exercise-induced hypotension, severe arrhythmia, or areas of heart w/ reduced blood

ST segment elevation - reasons

- With an evolving infarction
- In Prinzmetal's angina.

ST segment depression

- With typical exertional angina
- In a non-Q wave infarction.

Also:
- positive stress test.
- J point elevation
- Acute pericarditis
- Acute myocarditis
- Hyperkalemia
- Pulmonary embolism (S1Q3)
- Brugada syndrome
- Hypothermia

coronary cath - reasons?

testing & interventions; can be used w/ balloon angioplasty or stenting

echocardiogram

Transesophageal or transthoracic - 2D or 3D, Doppler, basically ultrasound of heart; can see movement of blood, valve regurgitation - can see valves & cardiomyopathies very well

Ashman phenomenon

Aberrant conduction of a supraventricular beat commonly seen in patients with atrial fibrillation; wide SV beat after a QRS complex that is preceded by a long pause.

How to interpret an EKG

1) Identify all waves & segments
2) Calculate rate
3) Determine intervals (PR, QT, QRS)
4) QRS axis
5) Hypertrophy & enlargement
6) Rhythm (normal P, wide QRS, P:QRS ratio, regular rhythm?)
7) Coronary artery disease
8) Other weird stuff

anterior leads

V2, V3, V4

left lateral leads

I, aVL, V5, V6

inferior leads

II, III, aVF

right ventricular leads

aVR, V1

Lead I - angle

+0º
left lateral

Lead II - angle

+60º
inferior

Lead III - angle

+120º
inferior

Lead aVF - angle

+90º
inferior

Lead aVR - angle

-150º - "la la land"
right ventricular

Lead aVL - angle

-30º
left lateral

Normal PR segment length

0.12 - 0.2 sec
3 - 5 small boxes

Normal QRS interval

0.06 - 0.1 sec
1 - 3 small boxes

Normal QT interval

40% of cardiac cycle

Normal P amplitude & duration

< 0.12 sec (3 small boxes)
< 2.5 mV (2.5 small boxes)

Positive P waves in?

left lateral (I, aVL, V5, V6) & inferior (II, III, aVF); usually most positive in II
& most negative in aVR

Often biphasic P in?

III, V1

Tall R waves in?

left lateral (I, aVL, V5, V6) & inferior (II, III, aVF)

Q waves in?

in one or several of left lateral leads (I, aVL, V5, V6), sometimes in inferior leads (II, III, aVF)

T wave positive in?

Usually in leads w/ tall R waves; left lateral (I, aVL, V5, V6) & inferior (II, III, aVF)

PR interval represents?

atrial depolarization & transmission through AV junction; supraventricular

QT interval represents?

Beginning of Q to end of T, ventricular depolarization → ventricular repolarization

Basic steps to interpret EKG

1) Identify all waves & segments
2) Calculate the rate
3) Determine intervals
4) Determine QRS axis
5) Recognize hypertrophy & enlargement

Waveform & orientation of I?

+0º
predominantly + (L arm +, R arm -)
left lateral

Waveform & orientation of II

+60º
predominantly + (R arm -, L Leg + (think "ll=LL")
inferior

Waveform & orientation of III

+120º
typically biphasic (L arm -, L Leg +)
inferior

Waveform & orientation of aVR

-150º "la la land"
predominantly - (R arm +, all others -); center of heart → R arm
right ventricular

Waveform & orientation of aVL

-30º
typically biphasic (L arm +, all others -); center of heart → L arm
left lateral

Waveform & orientation of aVF

+90º
predominantly + (both legs +, both arms +); center of heart → feet
inferior

Normal axis?

I +
aVF +

Right axis deviation?

I -
aVF +

Extreme right axis deviation?

I -
aVF -

Left axis deviation?

I +
aVF -

R atrium enlargement?

Leads II (parallel) & V1 (perpendicular; biphasic)
1) P wave > 2.5 mm in II, III, aVF
aka "p pulmonale"

Precise axis determination?

Look for most biphasic wave - it will be perpendicular to this.

p pulmonale?

RA enlargement, almost always related to pulmonary system; usually causes backup into the ventricle & atria, causing enlargement of atria

L atrium enlargement?

1) V1 terminal portion, P > 1mm below line
2) Terminal portion of P > 0.04 sec (1 small box)
"p mitrale"

p mitrale

LA enlargement due to mitral valve issue

RVH - criteria

1) R > S in V1
2) R progressively smaller from V1-V6
3) S > R in V6
- will cause right axis deviation
(also tall R in III)

LVH - precordial criteria

1. V5: R > 26 mm
2. V6: R > 18 mm
**3. S (V1 or V2) + R (V5 or V6) > 35 mm (most useful)
4. V6 R > V5 R

axis is not a great indicator (L axis shift)
Sensitivity is low, specificity is high

LVH - limb criteria

1. aVL: R > 13 mm
2. aVF: R > 21 mm
3. I: R > 14 mm
4. R (I) + S (III) > 25 mm

2º repolarization in ventricular hypertrophy - criteria?

1. Down-sloping ST segment depression
2. T wave inversion (R +, T -)
Tends to be most evident in leads most affected by size change
RVH = V1, V2
LVH = V5, V6

causes of arrhythmias

HISDEBS: hypoxia, ischemia/irritability, SNS, drugs, electrolytes, bradycardia, stretch (hypertrophy/enlargement)

symptoms of arrhythmias

none, "palpitations," light-headedness, syncope, angina, HF, sudden death

Types of arrhythmias

1. Sinus origin
2. Ectopic
3. Re-entrant (abnormally shaped path)
4. Conduction blocks (blocked signal)
5. Pre-excitation (shortcut in pathway)

Arrhythmias - 4 quick questions

1. Normal P waves?
2. Wide QRS? (> 0.12 sec indicates pacemaker below Bundle of His)
3. One P for every QRS?
4. Normal rate & rhythym?

Sinus bradycardia - criteria

HR < 60 bpm

Sinus tachycardia - criteria

HR > 100 bpm

Sinus arrhythmia

Appearance is ALMOST NORMAL:
Respiratory - Circulatory interaction
Rate INCREASES with INSPIRATION (IN=IN)

Sinus arrest - criteria

Rate: Regular or Bradycardia
P wave: Normal
QRS: Normal
Conduction: Normal
Rhythm: Irregular: length of pause ≠ multiple of normal rate (random)

Junctional Escape Beat/Rhythym - criteria

Rate: Bradycardia
P wave: Absent or Inverted P; if present, may occur during or after the QRS
QRS: Normal
Conduction: Escape beat: P-R interval < 0.12 seconds (if P present)
Rhythm: Irregular when it occurs (late)
If occurs 3 or more times in a row, is considered junctional escape rhythm

Sinus exit block - criteria

Rate: Regular or Bradycardia
P wave: Normal
QRS: Normal
Conduction: Normal
Rhythm:
Irregular: length of pause = multiple of normal rate
(Signal blocked leaving SA node; block is exactly equal to multiple of rate - one or more impulses "missed")

PACs (premature atrial contractions/atrial premature beats) - criteria

Rate: Regular underlying rate
P wave:
Abnormal - they originate from an ectopic pacemaker
QRS: Normal
Conduction:
Normal (except for PACs)
Rhythm:
Irregular when PACs occur (early)

PJCs (Premature Junctional Contractions)
AKA: Junctional Premature Beats

Rate: Regular underlying rate
P wave:
Absent or Inverted (like junctional escape)
QRS: Normal
Conduction:
PJC: P-R interval < 0.12 seconds (if P waves are present)
Rhythm:
Irregular when PJCs occur (early)

PSVT (Paroxysmal Supraventricular Tachycardia) AKA: AV nodal Re-entrant Tachycardia

Rate: Tachycardia (usually 150 - 200)
P wave: Absent or Inverted (like junctional escape)
QRS: Normal (may be wide, pseudo R')
Conduction: P-R interval < 0.12 seconds (if P)
Rhythm: Regular (abrupt onset and termination)
Carotid massage: slows or terminates

vagal stimulation

PNS stimulation - slows conduction through AV node; not if suspected carotid plaques
- valsalva, squatting, etc.

Atrial flutter

Rate:Atrial 250-350
Ventricular: 100 -175
P: Irregular or absent, often "saw tooth"
QRS: Normal
Conduction: AV Block (2:1 > 3:1, 4:1)
Rhythm: Regular (usually)
- Often underlying cardiac disease
Carotid massage: increases block

atrial fibrillation

Rate: Atrial 400-650;
Ventricular usually 120 - 180
P wave: Not present; often wavy baseline
QRS: Normal
Conduction: Variable AV conduction
Rhythm: Irregularly Irregular
- chaotic, unpredictable depolarizations w/i atrium, no atrial kick
- CAD, HTN, COPD, etc.
Carotid massage: may slow ventricular rate

MAT (Multifocal Atrial Tachycardia):

Rate: Atrial varies, Ventricular 100-200
P wave: ≥ 3 different 'P' waves
QRS: Normal (narrow)
Conduction: Variable AV conduction, P-R intervals vary
Rhythm: Irregularly irregular
- Various unpredictable atrial pacing sites
- Etiology: Often severe lung disease, longstanding COPD, etc.
Carotid massage: no effect

Wandering Atrial Pacemaker

Rate: Atrial & Ventricular 45 - 100
P wave: ≥ 3 different 'P' waves
QRS: Normal
Conduction: P-R intervals vary
Rhythm: Irregularly irregular
- slower form of MAT
Carotid massage: no effect

PAT (Paroxysmal (episodic) Atrial Tachycardia)

Rate: 100 - 200; Ventricular response 1:1 (or 2:1, 3:1, 4:1)
P wave: Usually present, abnormal
QRS: Normal
Conduction: P-R interval varies (due to ectopic sites)
Rhythm: Regular (may see warm up &/or cool down); unlike abrupt stop/start of PSVT; may be hard to distinguish
Carotid massage: no effect, or only mild slowing

MC ventricular arrhythmia?

PVCs - common in healthy people

bigeminy?

1:1 ratio of normal:PVC

trigeminy?

2:1 ratio of normal:PVC

PVCs (Premature Ventricular Contractions)

Rate: Regular underlying rate (usually); may happen occasionally in otherwise normal heart
P wave: Absent (or abnormal) in PVC
QRS: PVC: wide > 0.12 seconds; shape is bizarre; T wave inversion
Conduction: Normal before & after PVC
Rhythm: Irregular; may occur in singles, couplets or triplets

Reasons to worry about PVCs?

- Frequency increasing
- Runs of 3 or more consecutively
- Multiple PVC foci
- R-on-T Phenomenon
- PVC in acute MI

Multiple PVC foci

Beats 1 and 4 are sinus in origin. The other three beats are PVCs. The PVCs differ from each other in shape (multiform), and two occur in a row.

PVC - R on T

A PVC falls on the T wave of the second sinus beat, initiating a run of ventricular tachycardia.

Ventricular tachycardia

Rate: 120 - 200 usually
P wave:
Usually absent (unrelated to the QRS)
QRS: Wide & bizarre shape (PVCs)
Conduction: No correlation between 'P' if present and QRS
Rhythm: Regular or Irregular
Cannon A waves may be present
Carotid massage: no effect

Ventricular Fibrillation

Rate: Not attainable
P wave: Obscured by ventricular waves
QRS: No true QRS
Conduction: Chaotic electrical activity
Rhythm: Irregularly Irregular

Accelerated Idioventricular Rhythm

Rate: 50 - 100 usually (usually slow)
P wave: Obscured by ventricular waves (occur during ventricular contraction) - SA node slower than faster ventricular pacing than should be
QRS: Wide QRS
Conduction: Ventricular only
Rhythm: Regular

- benign rhythm that is sometimes seen during acute MI or early after reperfusion. - Rarely sustained, does not progress to vfib, rarely requires treatment

Torsades de Pointes

Rate: 120 - 200 usually
P wave: Obscured by ventricular waves
QRS: Wide QRS - "Twisting of the Points"
Conduction: Ventricular only
Rhythm: Slightly irregular

1º AV block

Rate: Normal (usually)
P wave: Normal
QRS: Normal
Conduction: P-R interval is > 0.2 seconds (delay) - slowing at the AV
Rhythm: Regular

2º AV Block - Wenckebach or Mobitz Type I

Rate: Normal or Bradycardia
P wave: Normal morphology & constant P-P interval
QRS: Normal
Conduction: P-R interval is progressively longer until P wave is blocked; the cycle begins again
Rhythm: Irregular

2º AV Block - Mobitz Type II

Rate: Bradycardia
P wave: Normal morphology & constant P-P interval
QRS: Normal or widened (usually associated with a bundle branch block)
Conduction:
P-R interval normal or prolonged (constant); some P waves are not conducted to ventricles (varies)

3º AV Block

Rate: Atrial 60-100; Ventricular 30-45
P wave: Normal with constant P-P interval ("marching through")
QRS: Usually widened (depends on location of escape pacemaker)
Conduction: Atrial & Ventricular activities are unrelated (complete block)
Rhythm: Irregular

Bundle branch blocks - general criteria

Due to changes related to the block, cannot say there is hypertrophy - BBB will make it look like hypertrophy

Rate: Regular or Bradycardia
P wave: Normal usually
QRS: Wide > 0.12 seconds
Conduction: Block occurs in the right or left bundle branches (or both)
Rhythm: Regular usually

Right bundle branch block (RBBB)

Right ventricular depolarization is delayed
Criteria:
- Wide QRS
- RSR' in V1, V2 ("bunny ears") with ST depression and T wave inversion
- Late S waves in I, aVL, V5, V6 (reciprocal changes)

Left bundle branch block (LBBB)

LV depolarization is delayed
Criteria:
- Wide QRS > 0.12
- Broad (+/- notched) R waves, ST depression & T-wave inversion in
I, aVL, V5, V6
- Broad S waves in V1, V2
- Left axis deviation may be present

MI evolution: three phases

Acute Onset:
- T-wave Peaking (Hyperacute T)
- T > ½ R wave

A Few Hours Later:
- T-wave Inversion
- ST Elevation (STEMI), NSTEMI
- "tombstone sign" (similar shape) - often associated with heart attack

Last: (days to weeks later)
- Significant Q-wave (true infarct)

Ischemic signs

ST elevation or ST depression:
> 1mm related to baseline (0.08 s (2 boxes) after QRS)

Also symmetric T-wave inversion in multiple precordial leads

NSTEMI

no Q wave or ST elevation
- T wave inversion
- ST DEPRESSION
- elevated cardiac enzymes (CPK-MB, troponin)
- high risk for later infarction!

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