Heart Conduction Pathway

• Conduction Pathway carries electrical signals throughout the heart in a specific sequence:

Conduction Pathway Steps

• Sinoatrial (SA) node initiates the signal.
• Interatrial tracts transmit the signal from the SA node to the left atrium.
• The signal passes through the atrium.
• Internodal tracts conduct the signal within the right atrium.
• The atrioventricular (AV) node delays the signal.
• The Bundle of His then transmits the signal from the AV node.
• Bundle branches carry the signal down the ventricular septum.
• Purkinje fibers distribute the signal throughout the ventricles.
• The ventricles contract.
• Depolarization (contraction) of the ventricles follows Purkinje fiber activation.
• The sinoatrial (SA) node's rate is 60-100 beats per minute.
• The atrioventricular (AV) node's rate is 40-60 beats per minute.
• The ventricle's rate is 20-40 beats per minute.
• Atria and ventricles contraction is separated by 0.1 second.
• The delay allows for coordinated blood movement, with atria contracting together, followed by ventricles.
• The ECG measures electrical activity of the heart from different angles, with each angle being called a lead, totaling 12 leads.

ECG Placement Leads

• ECG limb leads include:
• Right arm (white)
• Left arm (black)
• Right leg (green)
• Left leg (red)
• ECG precordial leads include:
• V1: 4th intercostal space (ICS) to the right of the sternum.
• V2: 4th ICS to the left of the sternum.
• V3: Midway between V2 and V4.
• V4: 5th ICS midclavicular line.
• V5: 5th ICS anterior axillary line.
• V6: 5th ICS midaxillary line.

Modified Chest Lead

• Continuous monitoring uses a modified chest lead
• Placement:
• Abdomen (negative electrode)
• Right shoulder (negative electrode)
• Left shoulder (positive electrode)
• It aligns with heart's electrical axis for clear P-wave visualization.

ECG Interpretation Guidelines

Voltage Measurements

• Each small block is 0.04 seconds.
• Five blocks equal one second.

Measuring Time

• Each small block is 0.1 mV.
• Five small blocks equal 0.5 mV.

Eight Steps for ECG Interpretation

• Measure heart rate (HR).
• Examine R-R interval.
• Examine P wave.
• Measure PR interval.
• Determine if each P wave is followed by QRS complex.
• Examine/measure QRS complex.
• Examine and measure QT interval.
• Diagnose rhythm.
• Ectopic beats are extra or premature beats, often described as "skipping" or "fluttering."

R-R Interval

• A constant R-R interval indicates a regular rhythm.
• A variable R-R interval indicates an irregular rhythm.

P Waves

• Smooth and upright deflection normally.
• Altered or missing P waves suggest sinoatrial (SA) node is not the primary pacemaker.

PR Interval

• PR interval measures the time for an impulse to travels from atria to ventricle.
• It starts at the beginning of the P wave to the beginning of the QRS complex.
• Normal range: 0.12 to 0.20 seconds (3-5 small boxes).
• Intervals greater than 5 boxes can indicate conduction delays, AV Node.

QRS Complex

• Normal range: 0.06-0.10 seconds (1-2.5 boxes).
• Evaluation includes assessing if they look identical and are abnormally wide.
• Abnormally wide complexes may indicate delayed conduction through bundle branches.

QT Interval

• QT interval should be less than half of the R-R interval (less than 0.40 seconds).
• Higher heart rates shorten QT.
• Lower heart rates lengthen QT.

P waves & QRS

• Should precede each QRS complex with a stable 1:1 relationship btwn these two waves

Rhythms Originating in the Atria

• Rhythm can be diagnosed by examining the ECG readings.

Premature Atrial Complexes (PAC)

• PAC are premature beats originating in SA node (atrial rate regular rate).
• PACs are can be identified by narrow QRS complex and upright and different P wave morphology.
• PACs can be caused by mimicry of Atria & automaticity

Wandering Atrial Pacemaker (WAP) / Multifocal Atrial Tachycardia (MAT)

• Pacemaking impulses originate from at least 3 different sites in the atria.
• Each impulse creates its own P wave, resulting in 3 different shapes of P waves and rapid heart rate
• WAP: heart rate is usually less than 100 beats per minute (slower atrial arrhythmia).
• MAT: heart rate is usually greater than 100 beats per minute. Causes:
• Irregular rhythm
• Three P waves with different shapes.
• Variable PR intervals.
• Normal QRS complexes (less than 0.12 seconds).
• WAP: medication Side Effects, hypoxia, vagal stimulation.
• MAT is caused by underlying medical conditions like COPD or heart disease.
• Adverse Effects:
• WAP = none
• MAT= reduced cardiac output if heart rate is too fast.

Determining Atrial Origin in Arrhythmias

• Check for matching upright P waves, atrial rate >100 at rest.
• Check for lack of P waves (wavy or sawtooth baseline)
• Presence of premature abnormal P wave, with or without QRS disrupting.
• High HR, regular rhythm, P waves unclear (potentially present and unsure).

Explore the heart's conduction pathway, tracing electrical signals from the SA node through the atria, AV node, Bundle of His, bundle branches, and Purkinje fibers. Understand the specific sequence and timing crucial for coordinated heart contractions and efficient blood movement. Learn about the intrinsic rates of the SA node, AV node and ventricles.