Basic Electrophysiology - Lecture Notes

Flashcards covering basic cardiac electrophysiology, types of cardiac cells, properties, the conduction system, ECG components, and rhythm interpretation based on Chapter 2 lecture materials.

Myocardial cells

Working or mechanical cells responsible for contraction.

Pacemaker cells

Specialized cells of the electrical conduction system that are able to form electrical impulses spontaneously and to alter the speed of electrical conduction.

Automaticity

The ability of pacemaker cells to initiate an electrical impulse without being stimulated from another source.

Excitability (irritability)

The ability of cardiac muscle cells to respond to an outside stimulus.

Conductivity

The ability of a cardiac cell to receive an electrical stimulus and conduct that impulse to an adjacent cardiac cell.

Contractility

The ability of cardiac cells to shorten, causing cardiac muscle contraction in response to an electrical stimulus.

Polarization

The resting phase of a cardiac cell.

Depolarization

The stimulation phase of a cardiac cell.

Repolarization

The recovery phase of a cardiac cell, equating to resting.

Atrial Depolarization

Represented on the ECG by the P wave.

Ventricular Depolarization

Represented on the ECG by the QRS complex.

Ventricular Repolarization

Represented on the ECG by the ST segment and T wave.

Effective refractory period (ERP)

The interval from the beginning of the action potential until the myocardial fiber is able to conduct another action potential, during which the cell cannot respond to further stimulation.

Relative refractory period (RRP)

Begins at the end of the ERP and ends when the cell membrane is almost fully repolarized; some cells can be stimulated by a stronger-than-normal stimulus.

Sinoatrial (SA) node

The primary pacemaker of the heart, with an intrinsic rate of $60$ to $100\text{ beats/min}$, usually supplied by the right coronary artery.

Secondary (subsidiary) pacemakers

Sites other than the SA node, such as the AV junction and Purkinje fibers, that can assume pacemaking responsibility with slower intrinsic rates.

Atrioventricular (AV) node

Structure that delays the conduction of the impulse from the atria to the ventricles.

Bundle of His (AV bundle)

Connects the AV node with bundle branches and has an intrinsic pacemaker rate of $40$ to $60\text{ beats/min}$.

Purkinje fibers

Fibers that receive impulses from bundle branches and relay them to ventricular myocardium, with an intrinsic pacemaker rate of $20$ to $40\text{ beats/min}$.

Accessory pathway

An atypical route that bypasses the AV node and bundle.

Altered automaticity

A condition where non-pacemaker cardiac cells depolarize spontaneously or a secondary pacemaker site increases its firing rate beyond normal.

Triggered activity

Abnormal electrical impulses (afterdepolarizations) occurring during repolarization when cells are normally quiet.

Reentry

A disorder of impulse conduction where an impulse returns to stimulate tissue that was previously depolarized.

Bipolar lead

A lead consisting of a positive and negative electrode, such as Leads I, II, and III.

Lead I

Records the difference in electrical potential between the left arm ($+$) and right arm ($-$) electrodes, viewing the lateral wall of the left ventricle.

Holter Monitor

A battery-powered continuous AECG recorder used for $24$ to $72\text{ hours}$ when symptoms occur frequently.

Implantable Loop Recorders

Small ECG recording devices implanted under the skin with a battery life of $2$ to $3\text{ years}$, used for infrequent symptoms.

ECG Paper Small Box

Measures $1\text{ mm}$ wide and $1\text{ mm}$ high, representing $0.04\text{ second}$.

ECG Paper Large Box

Comprised of $5$ small squares, representing $0.20\text{ second}$.

Isoelectric line (baseline)

A straight line recorded on the ECG when no electrical activity is detected.

P wave characteristics

Normally smooth and rounded, no more than $2.5\text{ mm}$ in height and $0.12\text{ second}$ in duration.

Pathologic Q wave

A Q wave more than $0.03\text{ second}$ in duration or more than $30\text{\%}$ of the following R wave height.

J point

The junction where the QRS complex and the ST segment meet.

PR interval

Represents total supraventricular activity and normally measures $0.12$ to $0.20\text{ second}$ in adults.

Artifact

Distortion of an ECG tracing by electrical activity noncardiac in origin, such as shivering, muscle tremors, or loose electrodes.