advanced ecgs for mlas

7/31/2019 Advanced ECGs for MLAs

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Advanced ECGs for MLAs

Cathie Cousins, RN, BScN, CCN(C)


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May 13, 2006 Cathie Cousins,RN BScN CCN(C) 2

Objectives

1. To review Basic Concepts for the 12-Lead ECG

To discuss the following on the 12-Lead ECG2. Bradycardia

3. Tachycardia

4. Ventricular Ectopy

5. ST and T wave changes

6. Pacemakers


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1. Basic Concepts

The heart is a pump with an electricalconduction system

2 basic types of cardiac cells in the heart

Myocardial cells or muscle cells

Specialized cells of the conduction system orpacemaker cells


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Electrical Axes and Vectors

Each of the 12 leads on the ECG has a different

pattern because each lead views the hearts

electrical axis from a different position

Atrial and ventricular depolarization and

repolarization generate an electric current

known as an electrical axis or vector (differentfrom the axis of a lead)


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Average of all the ventricular vectorspoints to the left and downward

Knowing the electrical axis of the heartenables us to determine the normal

pattern of each lead and the cause for

altered patterns in each lead


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Rate

Both the atrial and ventricular rates should bemeasured


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The Grid Method for Rate

Uses the distance between 2 sequentialcomplexes on the ECG

Each small square represents 0.04 seconds

- 1500 small squares in 1 minute- 300 large squares in 1 minute

Count the large squares between P waves for

atrial rate and R waves for ventricular rate

300 number of large squares = number of

beats/min


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Quick Tips 300 5 large squares = 60 bpm

5 or > large squares per minute = Bradycardia

300 3 large squares = 100 bpm

3 or > large squares per minute = Tachycardia


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2. Bradycardia

Bradycardia is a heart rate < 60/min

Bradycardia can be due a slow sinus rate, theorigin of the rhythm or an AV block:

- Sinus Bradycardia

- Junctional Rhythm

- Idioventricular Rhythm

- 2 AV Block Type I- 2 AV Block Type II

- 3 AV Block


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Sinus Bradycardia

Sinus node is pacing at a rate < 60/min

P wave, QRS normal


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Junctional Rhythm

Sinus node and atria fail to pace the heart.

AV junction paces at 40-60/min

No P wave or PR interval < 0.12, QRS normal


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Idioventricular Rhythm

Sinus node, atria, and AV junction fail to pace.

Ectopic pacemaker in the ventricles paces at

20-40/min

No P wave, QRS wide, ST & T waves oftenabnormal


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AV Blocks

2 Type I and 2Type II AV Blocks, sinus nodepaces the heart

Not ever P wave results in QRS,

QRS normal or wide


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3 AV Block, sinus node paces the heart

P waves do not result in QRSAV junction paces, QRS normal

Ventricles pace, QRS wide


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3. Tachycardia

Tachycardia is a heart rate > 100/min

Tachycardia can be due to:

- Sinus Tachycardia

- Supraventricular Tachycardia

- Ventricular Tachycardia


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Sinus Tachycardia

Sinus node is pacing at a rate > 100/min

P wave, QRS normal


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Superventricular Tachycardia

Ectopic focus in atria or AV junction paces the heart

or Abnormal conduction thru AV node

or Accessory pathway

P wave or no P wave, QRS narrow or wide,

rate > 150/min


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Ventricular Tachycardia

Ectopic pacemaker in ventricles paces the heart

No P wave, QRS wide and bizarre


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4. Premature Ventricular Contractions

QRS Duration

QRS duration - depolarization of right and leftventricles, from the endocardium to epicardium

Normal QRS duration - 0.06-0.10 sec

QRS duration > 0.10 sec, a conduction delayexists in the bundle branches, Purkinjie networkor ventricular myocardium, or ventricular ectopicconduction exists


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PVCs, premature ventricular complexes:

the premature beat originates in an ectopic

focus in one ventricle, it depolarizes that

ventricle, then the other

No P wave, QRS wide & bizarre, ST often

abnormal, T wave often opposite the rhythm

Multifocal PVCs come from more than oneectopic focus, each foci has a different shape


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1 PVC = a PVC

2 PVCs = couplet

3 PVCs = triplet

4 PVCs = ventricular tachycardia

Every 2nd

PVC = bigeminy Every 3rd PVC = trigeminy

Bigeminy or trigeminy can refer to any ectopic

beat so clarify -

eg. bigeminal PVCs or bigeminal PACs, etc.


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5a. ST Segments

ST segment = end of ventricular repolarization +

early part of ventricular repolarization

ST segment normally isoelectric

Ischemic + injured myocardial cells altered

membrane potentials, this allows a current toflow as seen in ST elevation + depression


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Measuring ST Segments

ST measurement = vertical difference betweenthe isoelectric line + end of QRS complex, the

J point


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ST Segment Elevation

ST segment elevation = >1 mm (>0.1 mV) abovebaseline after the J point

ST segment elevation due to severe injury

temporary until ischemia resolved or injuredheart tissue heals or dies

ST segments elevate in leads facing the injury

ST segments depress in leads opposite(reciprocal ) leads


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Types of ST Elevation in AMI


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Oth C C f


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Other Common Causes ofST Segment Elevation

Coronary artery vasospasm

Acute pericarditis

Ventricular aneursym

Hyperkalemia

Non-specific ST-T wave changes


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ST Segment Depression

ST segment depression = > 1 mm below

baseline after the J point

ST segment depression due to severe ischemia

temporary until ischemia resolved or heart tissueheals

ST segments depress in leads facing the

ischemia

ST segments elevate in opposite (reciprocal)

leads


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Types of ST Depression in AMI

Different types of

ST depression in AMI:

- downsloping

- horizontal

- upsloping

Oth C C f


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Other Common Causes of

ST Segment Depression

Left and right ventricular hypertrophy

Left and right bundle branch block Digitalis in therapeutic and toxic doses


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Acute MI Facing Leads Opposite Leads

Anterior

Septal V1-V2 None

Anterior V3-V4 None

Lateral I, aVL, & V5 or V6 II, III, & aVF

Inferior II, III, & aVF I & aVL

Posterior V7,V8, V9 on 18 lead V1-V4Right Ventricle V4R, V5R, V6R on 18 lead None


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5b. T waves

A T wave represents ventricular depolarization

T waves normally upright, rounded, and slightly

asymmetrical. Normally negative in aVR.

Normally 1/8 to 2/3 the height of the QRS

complex


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Abnormal T Waves in AMI

Normal Heart -

positive T wave

Subendocardial

Ischemia -

symmetrically

positive tall,

peaked T wave


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Subepicardial

Ischemia -symmetrically

negative deep T wave

Late phases in AMI -

deeply inverted

T waves with

abnormal Q waves


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6. Pacemakers


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The 3 Functions of Pacing

1. Sensing the ability of the pacemaker torecognize the patients intrinsic heartbeat

2. Pacing the pacemaker produces a stimuluseither when the sensing circuit does not detectan intrinsic heartbeat or at a predeterminedtime interval

3. Capturing the depolarization of themyocardium in response to pacing


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Pacemaker Codes

I Chamber(s) paced

II Chamber(s) sensed

III Response to sensing

IV Programmable function(s)

V Antitachyarrhythmia function(s)

Pacing Leads Sites Permanent


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Pacing Leads Sites - Permanent


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Pacing Leads Sites - Temporary


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Pacemaker Sites - Temporary

Transcutaneous

External Pacing


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Pacemaker Strip 1

1. Sensing

2. Pacing

3. Capturing


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Pacemaker Strip 2

1. Sensing2. Pacing

3. Capturing


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Thank You

Remember: It is the team that assists the

patient in achieving wellness.

Thank you and enjoy the exciting world of

12 Lead ECGs.

advanced ecgs for mlas

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