Cardiac Conduction and Dysrhythmias Practice Flashcards

Vocabulary practice flashcards covering cardiac conduction, EKG interpretation, telemetry rules, waveforms, intrinsic pacing rates, nursing interventions, and dysrhythmias.

Pulse Deficit

The numerical difference between the apical pulse and the radial pulse, occurring when heart contractions are not strong enough for the pulse wave to reach peripheral arteries.

Systolic Blood Pressure Threshold for Instability

A systolic blood pressure of less than $90\,\text{mmHg}$, which categorizes a patient presenting with a dysrhythmia as clinically unstable.

Synchronized Cardioversion

The delivery of an electrical shock timed specifically to align with the patient's $R\text{-wave}$ to avoid delivery during the T-wave refractory period; indicated for unstable patients who are alive.

Defibrillation

An unsynchronized electrical shock delivered regardless of cardiac cycle timing; indicated for patients in a dead or pulseless state (such as pulseless V-tach or V-fib).

Four Capabilities of Cardiac Myocytes

Conductivity, contractility, automaticity, and excitability.

Sinoatrial (SA) Node

The primary intrinsic pacemaker of the heart, located in the right atrium, which normally generates electrical impulses at a rate of $60\text{--}100\,\text{beats per minute}$.

Atrioventricular (AV) Node

A secondary pacemaker region that takes over cardiac pacing if the SA node fails, pacing the heart at an intrinsic rate of $40\text{--}60\,\text{beats per minute}$.

Bundle of His and Purkinje Fibers Intrinsic Rate

The backup pacing rate of the Bundle of His, bundle branches, and Purkinje fibers, which fire at an intrinsic rate of $20\text{--}40\,\text{beats per minute}$.

Isoelectric Line

The flat baseline on an EKG tracing representing zero electrical potential, from which positive deflections (upward) and negative deflections (downward) are measured.

Repolarization

The electrical recovery or relaxation phase of the heart cardiac cells (represented by the T-wave for the ventricles).

Depolarization

The electrical activation or contraction phase of the cardiac cells (represented by the P-wave for atria and QRS complex for ventricles).

P-Wave

The EKG waveform representing atrial depolarization starting from the SA node, normally round, upright, uniform in appearance, and preceding each QRS complex.

PR Interval

The time required for electrical conduction through the AV node, measured from the start of the P-wave to the start of the QRS complex; normal duration is $0.12\text{--}0.20\,\text{seconds}$ ($3\text{--}5\,\text{small boxes}$).

QRS Complex

The EKG waveform representing ventricular depolarization, with a normal duration defined as less than $0.10\,\text{seconds}$ (less than $2.5\,\text{small boxes}$).

Narrow vs. Wide QRS Complex

A narrow QRS ($< 0.10\,\text{seconds}$) indicates normal conduction originating in the Atria; a wide QRS ($> 0.10\,\text{seconds}$) indicates abnormal conduction originating in the ventricles.

T-Wave

The EKG wave representing ventricular repolarization (relaxation), where a spiked appearance can signal hyperkalemia.

QT Interval

The measurement representing the complete cycle of ventricular contraction and recovery; prolongation can lead to fatal dysrhythmias and can be caused by drugs such as Amiodarone and Zofran.

EKG Small Square Measurement

A single small box measuring $1\,\text{mm}$ horizontally, which represents $0.04\,\text{seconds}$ of time.

EKG Large Square Measurement

A grid box made up of $5 \times 5\,\text{small boxes}$ ($5\,\text{mm}$), which represents $0.20\,\text{seconds}$ of time.

Six-Second Strip Heart Rate Rule

A method to calculate heart rate on an EKG strip by counting the total number of QRS complexes in a $6\text{-second}$ interval and multiplying that count by $10$.

Precise Heart Rate Calculation Formula

A precise method to calculate heart rate by dividing $1500$ by the number of small squares between two consecutive R-waves ($\text{HR} = \frac{1500}{\text{small squares between R-waves}}$).

Normal Sinus Rhythm (NSR)

A regular rhythm characterized by evenly spaced R-waves, a heart rate of $60\text{--}100\,\text{beats per minute}$, round upright P-waves preceding each QRS, a PR interval of $0.12\text{--}0.20\,\text{seconds}$, and a narrow QRS ($< 0.10\,\text{seconds}$).

Sinus Bradycardia

A regular sinus rhythm possessing normal P-waves, PR interval, and narrow QRS complex, but with an abnormally slow rate of less than $60\,\text{beats per minute}$.

Atropine

The primary first-line medication administered to treat symptomatic, stable sinus bradycardia.

Transcutaneous Pacing

An emergency, temporary pacing method using large external pads connected to a defibrillator; highly painful because electrical current passes through skin and muscle tissue.

Pacemaker Capture

The successful depolarization of cardiac muscle following a pacemaker impulse, visualized on an EKG as a QRS complex immediately following every pacer spike.

Failure to Capture

A pacemaker complication where electrical spikes appear on the EKG without producing a subsequent QRS complex, resulting in absent ventricular contractions and inadequate perfusion.

Failure to Sense

A dangerous pacemaker malfunction where the device fails to detect intrinsic heart activity and fires spikes inappropriately, such as directly on a T-wave.

Sinus Tachycardia

A regular rhythm with normal P-waves, normal PR interval, and narrow QRS complex, but with an elevated rate exceeding $100\,\text{beats per minute}$.

Premature Atrial Contraction (PAC)

An early ectopic beat originating in the Atria characterized by an abnormally shaped P-wave occurring sooner than expected, followed by a narrow QRS complex.

Supraventricular Tachycardia (SVT)

A rapid, regular dysrhythmia with a heart rate of $150\text{--}250\,\text{beats per minute}$ and a narrow QRS complex, where P-waves are hidden inside preceding T-waves.

Adenosine

A rapid IV push medication administered closest to the heart followed by an immediate $20\,\text{mL}$ saline flush to briefly stop and reset cardiac rhythm in stable SVT.

Atrial Fibrillation (A-fib)

An irregularly irregular rhythm featuring chaotic atrial fibrillatory waves at $350\text{--}400\,\text{beats per minute}$, absence of distinct P-waves, loss of atrial kick, and a narrow QRS complex.

Rapid Ventricular Rate (RVR)

A complication in Atrial Fibrillation or Atrial Flutter where the ventricular rate exceeds $100\,\text{beats per minute}$, significantly reducing cardiac output and coronary perfusion.

Atrial Flutter

An atrial dysrhythmia characterized by classic regular saw-tooth flutter waves, an atrial rate up to $300\,\text{beats per minute}$, narrow QRS complexes, and regular or irregular ventricular response.

First-Degree AV Block

A cardiac conduction delay where every P-wave is conducted to the ventricles, but the PR interval is prolonged beyond $0.20\,\text{seconds}$ ($> 5\,\text{small boxes}$).

Third-Degree AV Block (Complete Heart Block)

A severe medical emergency defined by complete AV dissociation; P-waves and wide QRS complexes occur regularly but completely independent of one another at a slow ventricular rate ($20\text{--}40\,\text{beats per minute}$).

Premature Ventricular Contraction (PVC)

An ectopic impulse originating in the ventricles without a preceding P-wave, generating a wide and bizarre QRS complex.

Ventricular Tachycardia (V-tach)

A rapid ventricular rhythm ($100\text{--}250\,\text{beats per minute}$) with consecutive wide, bizarre QRS complexes and no P-waves; can occur with a pulse or pulseless.

Ventricular Fibrillation (V-fib)

A lethal, chaotic rhythm with quivering ventricles, no identifiable waves or QRS complexes, zero cardiac output, and no pulse; requires immediate CPR and defibrillation.

Torsades de Pointes

A form of polymorphic Ventricular Tachycardia ("twisting of the points") associated with a prolonged QT interval and hypomagnesemia; treated primarily with IV Magnesium.

Asystole

Complete absence of electrical activity in the heart (flatline); treated with immediate CPR and Epinephrine, NOT defibrillation.

Pulseless Electrical Activity (PEA)

A state where organized electrical activity is visible on the monitor screen, but there is no mechanical heart contraction or palpable pulse; treated with CPR and Epinephrine, NOT defibrillation.