Advanced ECG’s for MLA’s Cathie Cousins, RN, BScN, CCN(C)

Advanced ECG’s for MLA’s

Cathie Cousins, RN, BScN, CCN(C)

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. Bradycardia3. Tachycardia4. Ventricular Ectopy5. ST and T wave changes6. Pacemakers


1. Basic Concepts

• The heart is a pump with an electrical conduction system

• 2 basic types of cardiac cells in the heart

• Myocardial cells or “muscle” cells

• Specialized cells of the conduction system or “pacemaker” cells





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 (different from the axis of a lead)


• Average of all the ventricular vectors points to the left and downward

• Knowing the electrical axis of the heart enables us to determine the normal pattern of each lead and the cause for altered patterns in each lead



Rate

• Both the atrial and ventricular rates should be measured


The Grid Method for Rate

• Uses the distance between 2 sequential complexes 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


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


2. Bradycardia

• Bradycardia is a heart rate < 60/min

• Bradycardia can be due a slow sinus rate, the origin 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



Sinus Bradycardia

• Sinus node is pacing at a rate < 60/min• P wave, QRS normal


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


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 often abnormal


AV Blocks• 2° Type I and 2°Type II AV Blocks, sinus node

paces the heart • Not ever P wave results in QRS,

QRS normal or wide


• 3° AV Block, sinus node paces the heart• P waves do not result in QRS

AV junction paces, QRS normal

Ventricles pace, QRS wide






3. Tachycardia

• Tachycardia is a heart rate > 100/min

• Tachycardia can be due to:

- Sinus Tachycardia

- Supraventricular Tachycardia

- Ventricular Tachycardia



Sinus Tachycardia

• Sinus node is pacing at a rate > 100/min

• P wave, QRS normal


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


Ventricular Tachycardia

• Ectopic pacemaker in ventricles paces the heart• No P wave, QRS wide and bizarre






4. Premature Ventricular Contractions

QRS Duration

• QRS duration - depolarization of right and left ventricles, from the endocardium to epicardium

• Normal QRS duration - 0.06-0.10 sec

• QRS duration > 0.10 sec, a conduction delay exists in the bundle branches, Purkinjie network or ventricular myocardium, or ventricular ectopic conduction exists


• PVC’s, 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 PVC’s come from more than one ectopic focus, each foci has a different shape


• 1 PVC = a PVC• 2 PVC’s = couplet• 3 PVC’s = triplet• 4 PVC’s = ventricular tachycardia

• Every 2nd PVC = bigeminy• Every 3rd PVC = trigeminy

• Bigeminy or trigeminy can refer to any ectopic beat so clarify -

eg. bigeminal PVC’s or bigeminal PAC’s, etc.









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 to flow as seen in ST elevation + depression


Measuring ST Segments

• ST measurement = vertical difference between the isoelectric line + end of QRS complex, the “J” point”


ST Segment Elevation

• ST segment elevation = >1 mm (>0.1 mV) above baseline after the J point

• ST segment elevation due to severe injury temporary until ischemia resolved or injured heart tissue heals or dies

• ST segments elevate in leads facing the injury

• ST segments depress in leads opposite (reciprocal ) leads


Types of ST Elevation in AMI



Other Common Causes of ST Segment Elevation

• Coronary artery vasospasm• Acute pericarditis• Ventricular aneursym• Hyperkalemia• Non-specific ST-T wave changes


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 tissue heals

• ST segments depress in leads facing the ischemia

• ST segments elevate in opposite (reciprocal) leads


Types of ST Depression in AMI

Different types of

ST depression in AMI:

- downsloping

- horizontal

- upsloping


Other Common Causes of ST Segment Depression

• Left and right ventricular hypertrophy• Left and right bundle branch block• Digitalis in therapeutic and toxic doses


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-V4

Right Ventricle V4R, V5R, V6R on 18 lead None







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



Abnormal T Waves in AMI

• Normal Heart - positive T wave

• Subendocardial Ischemia - symmetrically positive tall, peaked T wave


• Subepicardial

Ischemia -

symmetrically

negative deep T wave

• Late phases in AMI -

deeply inverted

T waves with

abnormal Q waves







6. Pacemakers


The 3 Functions of Pacing

1. Sensing – the ability of the pacemaker to recognize the patient’s intrinsic heartbeat

2. Pacing – the pacemaker produces a stimulus either when the sensing circuit does not detect an intrinsic heartbeat or at a predetermined time interval

3. Capturing – the depolarization of the

myocardium in response to pacing


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


Pacing Leads Sites - Temporary


Pacemaker Sites - Temporary

Transcutaneous

– External Pacing


Pacemaker Strip 1

1. Sensing 2. Pacing3. Capturing


Pacemaker Strip 2

1. Sensing

2. Pacing

3. Capturing





Thank You

• Remember: It is the team that assists the patient in achieving wellness.

• Thank you and enjoy the exciting world of 12 Lead ECG’s.

Documents

Advanced ECG’s for MLA’s Cathie Cousins, RN, BScN, CCN(C)