Electrophysiology of the Heart ECG Monitoring The ECG

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Electrophysiology of the Heart

Electrophysiology of the Heart

ECG Monitoring • The ECG is a graphic representation of the heart's electrical activity

ECG Monitoring • The ECG is a graphic representation of the heart's electrical activity generated by depolarization and repolarization of the atria and ventricles

ECG Monitoring • Valuable diagnostic tool for identifying cardiac abnormalities including: – Abnormal heart

ECG Monitoring • Valuable diagnostic tool for identifying cardiac abnormalities including: – Abnormal heart rates and rhythms – Abnormal conduction pathways – Hypertrophy or atrophy of portions of the heart – Approximate location of ischemic or infarcted cardiac muscle

ECG Monitoring • The ECG tracing is only a reflection of the heart's electrical

ECG Monitoring • The ECG tracing is only a reflection of the heart's electrical activity • It does not provide information regarding mechanical events such as force of contraction or blood pressure

Voltage • Voltage may be: – Positive--seen as an upward deflection on the ECG

Voltage • Voltage may be: – Positive--seen as an upward deflection on the ECG tracing – Negative--seen as a downward deflection on the ECG tracing – Isoelectric--no electrical current detected • Seen as a straight baseline on the ECG

Application of Monitoring Electrodes • Electrodes are pre-gelled, stick-on disks that can easily be

Application of Monitoring Electrodes • Electrodes are pre-gelled, stick-on disks that can easily be applied to the chest wall • When applying electrodes: – Cleanse the area with alcohol to remove dirt and body oil – Use the inner surfaces of the arms and legs when attaching electrodes to extremities

Application of Monitoring Electrodes • When applying electrodes: – Trim excess body hair (if

Application of Monitoring Electrodes • When applying electrodes: – Trim excess body hair (if necessary) before placing the electrodes – Attach the electrodes to the prepared site – Attach the ECG cables to electrodes – Turn on the ECG monitor and obtain a baseline tracing

Monitoring Electrodes • If the signal is poor, recheck the cable connections and electrode

Monitoring Electrodes • If the signal is poor, recheck the cable connections and electrode contact with the patient's skin • Other causes of a poor signal include: – Excessive body hair – Dried conductive gel – Poor electrode placement – Diaphoresis

ECG Monitoring

ECG Monitoring

ECG Monitoring

ECG Monitoring

ECG Monitoring

ECG Monitoring

Calibration • The sensitivity of the 12 -lead ECG machine is standardized • When

Calibration • The sensitivity of the 12 -lead ECG machine is standardized • When properly calibrated, a 1 -m. V electrical signal produces a 10 -mm deflection (two large squares) on the ECG tracing Figure 28 -21

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram

The Electrocardiogram – Refractory Periods • Absolute – no other electrical impulse can be

The Electrocardiogram – Refractory Periods • Absolute – no other electrical impulse can be generated • Relative – very dangerous time another electrical impulse can interfere with the rhythm – V Tach can occur or V Fib

Conduction System of the Heart • Sinoatrial (SA) node • Atrioventricular (AV) node /

Conduction System of the Heart • Sinoatrial (SA) node • Atrioventricular (AV) node / bundle of His • Purkinje fibers Figure 6 -41

Normal Conduction • Sequence of normal impulse conduction – SA node – Both atria

Normal Conduction • Sequence of normal impulse conduction – SA node – Both atria • Atrial contraction – – AV node Bundle of His Purkinje fibers Both ventricles • Ventricular contraction Figure 6 -41

Inherent Rates • SA node – 60 -100 • AV node – 40 -60

Inherent Rates • SA node – 60 -100 • AV node – 40 -60 • Ventricular – 20 -40

P Wave • First positive (upward) deflection on ECG • Represents atrial depolarization •

P Wave • First positive (upward) deflection on ECG • Represents atrial depolarization • Usually rounded and precedes the QRS complex – Begins with first positive deflection from baseline – Ends at point where wave returns to baseline Figure 28 -22

P Wave • Duration normally 0. 10 second or less • Amplitude normally 0.

P Wave • Duration normally 0. 10 second or less • Amplitude normally 0. 5 to 2. 5 mm • Usually followed by a QRS complex unless conduction disturbances are present Figure 28 -22

PR Interval • Represents the time it takes for an electrical impulse to be

PR Interval • Represents the time it takes for an electrical impulse to be conducted through the atria and the AV node up to the instant of ventricular depolarization – Measured from the beginning of the P wave to the beginning of the next deflection on the baseline (the onset of the QRS complex) • Normal is 0. 12 -0. 20 second Figure 28 -25

PR Interval • A normal PR interval indicates that the electrical impulse has been

PR Interval • A normal PR interval indicates that the electrical impulse has been conducted through the atria, AV node, and bundle of His normally and without delay • PRI < 0. 2 secs Figure 28 -25

QRS Complex • Generally composed of three individual waves: the Q, R, and S

QRS Complex • Generally composed of three individual waves: the Q, R, and S waves • Begins at the point where the first wave of the complex deviates from the baseline • Ends where the last wave of the complex begins to flatten at, above, or below the baseline Figure 28 -25

QRS Complex • Direction of the QRS complex may be: – Predominantly positive (upright)

QRS Complex • Direction of the QRS complex may be: – Predominantly positive (upright) – Predominantly negative (inverted) – Biphasic (partly positive, partly negative)

QRS Complex • The normal QRS complex is narrow and sharply pointed • Duration

QRS Complex • The normal QRS complex is narrow and sharply pointed • Duration is generally 0. 08 to 0. 12 second • Amplitude normally varies from less than 5 mm to more than 15 mm Figure 28 -25

Q Wave • The first negative (downward) deflection of the QRS complex on the

Q Wave • The first negative (downward) deflection of the QRS complex on the ECG – May not be present in all leads • Represents depolarization of the interventricular septum Figure 28 -25

R Wave • First positive deflection after the P wave – Subsequent positive deflections

R Wave • First positive deflection after the P wave – Subsequent positive deflections in the QRS complex that extend above the baseline and that are taller than the first R wave are called R prime (R’), R double prime (R’’), and so on Figure 28 -23

S Wave • Negative deflection that follows the R wave – Subsequent negative deflections

S Wave • Negative deflection that follows the R wave – Subsequent negative deflections are called S prime (S’), S double prime (S”), and so on • R and S waves represent the sum of electrical forces resulting from depolarization of the right and left ventricles Figure 28 -25

QRS Complex • Follows the P wave • Marks the approximate beginning of mechanical

QRS Complex • Follows the P wave • Marks the approximate beginning of mechanical systole of the ventricles, which continues through the onset of the T wave • Represents ventricular depolarization – Conduction of an electrical impulse from the AV node through the bundle of His, Purkinje fibers, and the right and left bundle branches

QRS Complex Figure 28 -22

QRS Complex Figure 28 -22

ST Segment • Represents the early phase of repolarization of the right and left

ST Segment • Represents the early phase of repolarization of the right and left ventricles • Immediately follows the QRS complex and ends with the onset of the T wave Figure 28 -24 A

ST Segment • The point at which the ST segment “takes off” from the

ST Segment • The point at which the ST segment “takes off” from the QRS complex is called the J point Figure 28 -24 D

ST Segment • The position of the ST segment is commonly judged as normal

ST Segment • The position of the ST segment is commonly judged as normal or abnormal using the baseline of the PR or TP interval as a reference – ST segment elevation – ST segment depression Figure 28 -24 A, B, & C

ST Segment • Abnormal ST segments may be seen in: – Infarction – Ischemia

ST Segment • Abnormal ST segments may be seen in: – Infarction – Ischemia – Pericarditis – After digitalis administration – Other disease states

T Wave • Represents repolarization of ventricular myocardial cells • Occurs during the last

T Wave • Represents repolarization of ventricular myocardial cells • Occurs during the last part of ventricular systole • May be above or below the isoelectric line and is usually slightly rounded and slightly asymmetrical Figure 28 -25

T Wave • Deep and symmetrically inverted T waves may suggest cardiac ischemia •

T Wave • Deep and symmetrically inverted T waves may suggest cardiac ischemia • A T wave elevated more than half the height of the QRS complex (peaked T wave) may indicate a new onset of myocardial ischemia or hyperkalemia

Artifact • A series of deflections on the ECG display or tracing produced by

Artifact • A series of deflections on the ECG display or tracing produced by factors other than the heart's electrical activity • Common causes of artifact: – – – Improper grounding of the ECG machine Patient movement Loss of electrode contact with the patient's skin Patient shivering or tremors External chest compressions

Artifact - Muscle Tremors Figure 28 -26 A

Artifact - Muscle Tremors Figure 28 -26 A

Artifact - AC (60 cycle) Interference Figure 28 -26 B

Artifact - AC (60 cycle) Interference Figure 28 -26 B

Artifact – Loose Electrode Figure 28 -26 C

Artifact – Loose Electrode Figure 28 -26 C

Reading ECG’s

Reading ECG’s

ECG Measurements 1 sec 0. 20 sec 0. 04 sec 5 large squares= 25

ECG Measurements 1 sec 0. 20 sec 0. 04 sec 5 large squares= 25 mm = 1 second 1 large square = 5 mm = 5 small squares =0. 20 seconds 1 small square = 1 mm = 0. 04 seconds 0. 1 m. V Voltage Standard calibration for an ecg is 10 mm=1 m. V, or 1 mm = 0. 1 m. V Time

Rate Determination The Six Second Method 1. ECG paper is marked at three second

Rate Determination The Six Second Method 1. ECG paper is marked at three second intervals (15 large boxes) 2. Count the R Waves in 6 seconds (30 large boxes/two 3 -second intervals) 3. Multiply the number of complexes by 10 to determine the rate (in this example 7 X 10 = 70) 1 2 3 4 5 6 7

Interpreting ECG’s • Questions to ask – Are there P waves? – Do they

Interpreting ECG’s • Questions to ask – Are there P waves? – Do they all look alike? – PRI – short or long? – QRS – tight or wide? – Any extra P waves? – Any extra QRS complexes? – What is the rate? – WHAT IS THE UNDERLYING RHYTHM?

Atrial Rhythms • Sinus rhythm – – P waves PRI – normal No extra

Atrial Rhythms • Sinus rhythm – – P waves PRI – normal No extra beats Rate 60 - 100

 • Sinus Bradycardia – – P waves PRI – normal No extra beats

• Sinus Bradycardia – – P waves PRI – normal No extra beats Rate is < 60

 • Sinus Tachycardia – – P waves PRI – normal No extra beats

• Sinus Tachycardia – – P waves PRI – normal No extra beats Rate is 100 -150

 • Wandering Atrial Pacemaker – P waves are present but they do not

• Wandering Atrial Pacemaker – P waves are present but they do not look alike – QRS intervals are regular

 • Wolfe-Parkinson-White – P waves are present – Delta wave – Reentry rhythm

• Wolfe-Parkinson-White – P waves are present – Delta wave – Reentry rhythm

 • Sinus Rhythm with unifocal Premature Ventricular Contractions (PVC) – – – P

• Sinus Rhythm with unifocal Premature Ventricular Contractions (PVC) – – – P waves are present PRI is normal Some QRS complexes come early and are wide Premature QRS complexes look alike Must differentiate whether the PVC’s look alike or not

 • Sinus Rhythm with multifocal PVC’s – – – P waves are present

• Sinus Rhythm with multifocal PVC’s – – – P waves are present PRI is normal Some QRS complexes come early and are wide Early QRS complexes are different Must differentiate whether the PVC’s look alike or not

 • Sinus Rhythm with couplets – P waves are present – PRI is

• Sinus Rhythm with couplets – P waves are present – PRI is normal – 2 QRS complexes come early together and are wide

 • Sinus Rhythm with a run of V Tach – P waves are

• Sinus Rhythm with a run of V Tach – P waves are present – PRI is normal – 3 or more PVC’s together

 • Sinus Rhythm with R on T phenomenon – P waves are present

• Sinus Rhythm with R on T phenomenon – P waves are present – PRI is normal – Can go into V Fib

 • Sinus Rhythm with bigeminy – Underlying rhythm is a SR – Every

• Sinus Rhythm with bigeminy – Underlying rhythm is a SR – Every other QRS complex is a PVC

 • Sinus Rhythm with an aberrant conduction or Bundle Branch Block – P

• Sinus Rhythm with an aberrant conduction or Bundle Branch Block – P waves are present – PRI is normal – QRS complex is wide

 • Atrial fibrillation – No discernable P waves – QRS – irregularly irregular

• Atrial fibrillation – No discernable P waves – QRS – irregularly irregular

 • Atrial Flutter – P waves are flutter waves or “sawtooth pattern” –

• Atrial Flutter – P waves are flutter waves or “sawtooth pattern” – QRS can be regular or irregular

Heart Blocks • Sinus Rhythm with 1 st degree HB – – P waves

Heart Blocks • Sinus Rhythm with 1 st degree HB – – P waves are present PRI – longer than normal QRS complex is usually narrow MUST GIVE AN UNDERLYING RHYTHM

 • 2 nd degree HB Type I or Wenckebach – P waves are

• 2 nd degree HB Type I or Wenckebach – P waves are present – Extra P waves – PRI gets progressively longer then you get a “dropped QRS”

 • 2 nd degree HB Type II or Classic 2 nd degree HB

• 2 nd degree HB Type II or Classic 2 nd degree HB – P waves are present – Extra P waves – PRI stays the same but then you get a “dropped QRS”

 • 3 rd degree HB or Complete HB – – – – P

• 3 rd degree HB or Complete HB – – – – P waves are present P waves map out QRS complexes are usually wide QRS complexes map out P waves do not map out with the QRS complexes PRI has no consistency Sometimes it looks like the P waves are marching towards the QRS

Junctional Rhythms • Junctional Rhythm – No P waves – QRS complex is tight

Junctional Rhythms • Junctional Rhythm – No P waves – QRS complex is tight – Rate 40 -60

 • Junctional Bradycardia – No P waves – QRS complex is tight –

• Junctional Bradycardia – No P waves – QRS complex is tight – Rate < 40

 • Accelerated Junctional Rhythm – No P waves – QRS complex is tight

• Accelerated Junctional Rhythm – No P waves – QRS complex is tight – Rate 60 -100

 • Junctional Tachycardia – No P waves – QRS complex is tight –

• Junctional Tachycardia – No P waves – QRS complex is tight – Rate 100 -150

Ventricular Rhythms • Idioventricular Rhythm – – No P waves QRS complex is wide

Ventricular Rhythms • Idioventricular Rhythm – – No P waves QRS complex is wide Rhythm is regular Rate 20 -40

 • Agonal Idioventricular Rhythm – – No P waves QRS complex is extremely

• Agonal Idioventricular Rhythm – – No P waves QRS complex is extremely wide Will not produce a pulse Rate < 20

 • Accelerated Idioventricular Rhythm – – No P waves QRS complex is wide

• Accelerated Idioventricular Rhythm – – No P waves QRS complex is wide Rhythm is regular Rate 40 -100

 • “Slow” Ventricular Tachycardia – – No P waves QRS complex is wide

• “Slow” Ventricular Tachycardia – – No P waves QRS complex is wide Rhythm is regular Rate 100 -150

 • Ventricular Tachycardia – – No P waves QRS complex is wide Rhythm

• Ventricular Tachycardia – – No P waves QRS complex is wide Rhythm is regular Rate > 150

 • Ventricular Fibrillation – – No P waves QRS complex is wide and

• Ventricular Fibrillation – – No P waves QRS complex is wide and bizarre Rhythm is erratic Rate > 150

 • Fine Ventricular Fibrillation – – No P waves QRS complex is wide,

• Fine Ventricular Fibrillation – – No P waves QRS complex is wide, bizarre and small Rhythm is erratic Rate > 150

 • Coarse Ventricular Fibrillation – – No P waves QRS complex is wide,

• Coarse Ventricular Fibrillation – – No P waves QRS complex is wide, bizarre and large Rhythm is erratic Rate > 150

 • Torsades de Pointes (Turning of the Points) – – – No P

• Torsades de Pointes (Turning of the Points) – – – No P waves QRS complex is wide, bizarre and large QRS complexes seem to face different directions Rhythm is erratic Rate > 150

 • Asystole – – No P waves No QRS complexes “Flatline” Must confirm

• Asystole – – No P waves No QRS complexes “Flatline” Must confirm in at least two leads

 • Ventricular Pacemaker – P waves may or may not be present –

• Ventricular Pacemaker – P waves may or may not be present – Pacemaker spikes just prior to QRS complex – QRS complexes are wide

 • Atrial Pacemaker – Pacemaker spikes just prior to P waves – QRS

• Atrial Pacemaker – Pacemaker spikes just prior to P waves – QRS complexes are narrow

 • Atrial Ventricular Pacemaker or AV Sequential Pacemaker – Pacemaker spikes just prior

• Atrial Ventricular Pacemaker or AV Sequential Pacemaker – Pacemaker spikes just prior to P wave – Pacemaker spikes just prior to QRS complex – QRS complexes are wide

Any Questions? ? ?

Any Questions? ? ?