Lab & Diag Exam 3

SR c 1 degree AV block

Interpretation?

Prolonged physiologic block in the AV node and PRI exceeding 0.20 seconds with a 1:1 P:QRS ratio

What is the primary diagnostic criterion for First-Degree Heart Block?

Prolonged PR interval > 0.20 seconds with a 1:1 P:QRS ratio

What is the primary diagnostic criterion for First-Degree Heart Block?

Prolonged physiologic block in the AV node

What is the underlying electrophysiologic mechanism of First-Degree Heart Block?

Regular

What is the rhythm regularity of First-Degree Heart Block?

Normal

What is the typical QRS complex width in First-Degree Heart Block?

None

How many dropped beats occur in First-Degree Heart Block?

Medication, vagal stimulation, and underlying disease

What are three common causes of First-Degree Heart Block?

Wenckebach

What is Mobitz I Second-Degree Heart Block also commonly called?

PR interval progressively lengthens between successive beats until a QRS complex is dropped

What is the characteristic PR interval pattern in Mobitz I Second-Degree Heart Block?

It shortens with each beat preceding the dropped beat

How does the R-R interval change during the cycle in Mobitz I Second-Degree Heart Block?

Regularly irregular

What is the overall rhythm regularity in Mobitz I Second-Degree Heart Block?

A diseased AV node with a long refractory period

What cellular or nodal pathology causes Mobitz I Second-Degree Heart Block?

Variable, such as 2:1, 3:2, 4:3, or 5:4

What is the P:QRS ratio in Mobitz I Second-Degree Heart Block?

Constant PR interval across all conducted beats before a dropped beat

What is the key diagnostic PR interval feature in Mobitz II Second-Degree Heart Block?

Below the AV node, usually in the Bundle of His

Where is the anatomical site of conduction block located in Mobitz II Second-Degree Heart Block?

Structural damage such as fibrosis, infarction, or necrosis

What type of pathology typically causes Mobitz II Second-Degree Heart Block?

All-or-nothing conduction failure

How does the conduction mechanism of Mobitz II differ from the progressive failure of Mobitz I?

Progression to complete (Third-Degree) heart block

What dangerous clinical event is Mobitz II Second-Degree Heart Block a harbinger of?

Autoimmune disease, inflammatory disease, past cardiac surgery, MI, hyperkalemia, and drugs

What are potential etiologies of Mobitz II Second-Degree Heart Block?

Complete block at the AV node resulting in AV dissociation

What is the hallmark electrophysiologic defect in Third-Degree Heart Block?

P waves fire regularly at their own rate, completely independent of QRS complexes

How do P waves relate to QRS complexes in Third-Degree Heart Block?

Variable with no repeating pattern

What is the behavior of the PR interval in Third-Degree Heart Block?

Junctional escape rhythm or ventricular escape rhythm

What two types of escape rhythms can drive ventricular contraction in Third-Degree Heart Block?

Normal QRS width

What QRS complex width is expected when the escape rhythm in Third-Degree Heart Block originates in the junction?

Wide QRS width

What QRS complex width is expected when the escape rhythm in Third-Degree Heart Block originates in the ventricles?

Regular, but P wave rate and QRS rate are different and dissociated

What is the regularity and rate relationship in Third-Degree Heart Block?

Lead I and Lead aVF

Which two limb leads are primarily analyzed to determine the electrical axis quadrant?

Lead I positive and Lead aVF positive

What QRS polarities in Lead I and Lead aVF indicate a Normal electrical axis?

Lead I positive and Lead aVF negative

What QRS polarities in Lead I and Lead aVF indicate Left Axis Deviation?

Lead I negative and Lead aVF positive

What QRS polarities in Lead I and Lead aVF indicate Right Axis Deviation?

Lead I negative and Lead aVF negative

What QRS polarities in Lead I and Lead aVF indicate Extreme Axis Deviation?

0 degrees to +90 degrees

What degree range defines a normal QRS axis on the hexaxial grid?

-30 degrees to -90 degrees

What degree range defines Left Axis Deviation on the hexaxial grid?

+90 degrees to +180 degrees

What degree range defines Right Axis Deviation on the hexaxial grid?

-90 degrees to 180 degrees

What degree range defines Extreme Right Axis Deviation on the hexaxial grid?

Positive (upright)

Is Lead I positive or negative in Left Axis Deviation?

Negative (downward)

Is Lead aVF positive or negative in Left Axis Deviation?

Negative (downward)

Is Lead I positive or negative in Right Axis Deviation?

Positive (upright)

Is Lead aVF positive or negative in Right Axis Deviation?

V1 through V6

Which leads make up the precordial lead set evaluating the horizontal (Z) axis?

Predominantly negative

What is the normal QRS complex orientation in lead V1?

Predominantly positive

What is the normal QRS complex orientation in lead V6?

Around lead V3

Where is the normal precordial QRS transition zone located?

Septal wall

Which anatomical region of the heart is monitored by leads V1 and V2?

Anterior wall

Which anatomical region of the heart is monitored by leads V3 and V4?

Lateral wall

Which anatomical region of the heart is monitored by leads V5 and V6?

Inferior wall

Which anatomical region of the heart is monitored by leads II, III, and aVF?

Lateral wall

Which anatomical region of the heart is monitored by limb leads I and aVL?

Mobitz I (Wenckebach)

Which heart block displays grouped beating on the ECG strip?

Third-Degree Heart Block

In which heart block do atria and ventricles fire completely independently ("to their own drummer")?

First-Degree Heart Block

Which heart block maintains a 1:1 P:QRS ratio while displaying a PR interval greater than 0.20 seconds

SR c 1 degree AV block

Interpretation?

Normal Axis deviation

Axis Interpretation?

Left Axis Deviation

Axis Interpretation?

Right Axis Deviation

Axis Interpretation?

Fibrosis along the bundle branches

What is the primary underlying cause of altered electrical conduction in Bundle Branch Blocks?

Delay in complete ventricular depolarization

What fundamental electrophysiologic abnormality causes the widened QRS complex in Bundle Branch Blocks?

Incomplete Bundle Branch Block

What is the diagnosis when an ECG shows BBB characteristics but the QRS duration is less than 0.12 seconds?

Complete Bundle Branch Block

What is the diagnosis when an ECG shows BBB characteristics with a QRS duration of 0.12 seconds or greater?

Greater than 0.12 seconds

What QRS duration criterion must be met to diagnose a complete Right Bundle Branch Block?

rSR' pattern (rabbit ears)

What classic QRS complex morphology is seen in lead V1 in Right Bundle Branch Block?

Leads I and V6

In which ECG leads do you typically find slurred S waves in Right Bundle Branch Block?

Old or new myocardial infarction

What does a QR' or qR' pattern in lead V1 indicate in a patient with Right Bundle Branch Block?

Right ventricular hypertrophy, pulmonary embolism, ischemic heart disease, rheumatic heart disease, ASD, and degenerative conduction disease

What are common etiologies of Right Bundle Branch Block?

Yes, standard criteria can still be used

Can Left Ventricular Hypertrophy be diagnosed on an ECG in the presence of a Right Bundle Branch Block?

Greater than 0.12 seconds

What QRS duration criterion is required to diagnose Left Bundle Branch Block?

Leads I, aVL, and V6

In which leads are broad, monomorphic R waves characteristically seen in Left Bundle Branch Block?

Broad S wave (with or without a small r wave)

What QRS morphology is typically observed in lead V1 in Left Bundle Branch Block?

Leads I and V6

In Left Bundle Branch Block, which leads characteristically demonstrate a lack of normal septal Q waves?

Left ventricular hypertrophy, systemic hypertension, ischemic heart disease, dilated cardiomyopathy, acute MI, hyperkalemia, and digoxin toxicity

What are major clinical causes of Left Bundle Branch Block?

No, ventricular hypertrophy cannot be accurately diagnosed

Can Left or Right Ventricular Hypertrophy be diagnosed on an ECG in the presence of Left Bundle Branch Block?

Left Bundle Branch Block

Which bundle branch block severely limits the clinician's ability to evaluate an ECG for acute ischemia or infarction?

Intraventricular Conduction Delay (IVCD)

What term describes a QRS complex duration greater than 0.10 seconds that does not meet full criteria for RBBB or LBBB?

QRS duration between 0.10 and 0.11 seconds localized to specific leads

What defines a localized Intraventricular Conduction Delay?

QRS duration of 0.12 seconds or greater without typical LBBB or RBBB criteria

What defines a generalized Intraventricular Conduction Delay?

Ventricular rhythm, LBBB, RBBB, and generalized IVCD

What are the four main cardiac causes of a widened QRS complex greater than 0.12 seconds?

Hyperkalemia and tricyclic antidepressant toxicity

What two severe metabolic or toxicological conditions can cause supraventricular wide QRS conduction delays?

A block in one of the fascicles of the left bundle branch

What is the definition of a cardiac hemiblock?

Left Anterior Fascicular Block and Left Posterior Fascicular Block

What are the two types of left-sided hemiblocks?

Right Bundle Branch Block combined with a block in either the left anterior or left posterior fascicle

What constitutes a bifascicular block?

Axis determination

What ECG measurement plays the most prominent role in diagnosing fascicular hemiblocks?

Set the pace of cardiac depolarization and contraction to maintain cardiac output

What is the primary therapeutic function of an artificial cardiac pacemaker?

Pulse generator and pacing leads

What are the two main physical components of a pacemaker system?

Ability to deliver electrical shocks to defibrillate lethal ventricular arrhythmias

What additional capability does an Implantable Cardiac Defibrillator (ICD) have compared to a standard pacemaker?

Bipolar leads

What type of leads is most commonly used in modern pacemakers?

Atrial, Ventricular, Dual-chamber (A-V), and Biventricular

What are the four major chamber-specific types of pacing devices?

Leadless pacemaker

What type of miniature pacemaker is implanted directly into the heart chamber without transvenous leads?

Transcutaneous pacing via external defibrillator pads

What is the non-invasive method of temporary external cardiac pacing?

Pacemaker detecting intrinsic depolarization of native myocardial cells

What is meant by pacemaker sensing?

Under-pacing (inhibition of needed pacing spikes)

What is the clinical consequence of pacemaker oversensing?

Over-pacing (inappropriate delivery of electrical spikes)

What is the clinical consequence of pacemaker undersensing?

Successful myocardial depolarization resulting from a pacemaker output spike

What is meant by pacemaker capture?

Electrical threshold

What term refers to the minimum voltage required from a pacemaker to consistently cause myocardial depolarization?

Under-pacing or absent ventricular response following a pacer spike

What is the ECG result of pacemaker capture failure?

Maintenance or improvement of cardiac output

What is the primary hemodynamic goal when initiating cardiac pacing?

Narrow vertical deflection (pacer spike) preceding a P wave, wide QRS, or both

What characteristic ECG deflection confirms the presence of an active artificial pacemaker

Extreme axis deviation

Interpretation Axis?

2 degree AV block Mobitz I (Wenchebach)

Interpretation?

2 Degree AV block Mobitz II

Interpretation?