Cardiac Conduction Disorders - Exam 2 Review

What is sinus bradycardia?

A slow rhythm originating in the SA node with a rate below 60 bpm; Each beat has normal P wave, QRS, and T wave; Common in rest, athletes, or due to medications; Causes: normal at rest, trained athletes, drug side effects; Effects/Symptoms: ↓ cardiac output, dizziness or lightheadedness if rate too low~

What is sinus tachycardia?

A fast rhythm originating in the SA node with a rate >100 bpm (usually 100–150 bpm); Normal P wave, QRS, and T wave; Can exceed 150 bpm during extreme stress/exertion; Causes: fever, anemia, hypermetabolic states, sympathetic stimulation, stimulant drugs; Effects/Symptoms: ↓ stroke volume & LV filling time, may reduce cardiac output~

What are premature atrial contractions (PACs)?

Early electrical impulses originating above the AV junction, causing a premature heartbeat; Early P wave before next expected beat, usually followed by normal QRS; Causes: caffeine, tobacco, stress, fatigue, heart disease; Effects/Symptoms: usually benign, may feel like “skipped” or “extra” beats~

What are premature ventricular contractions (PVCs)?

Extra early beats that begin in the ventricles instead of the atria; Wide, bizarre QRS complex, often not followed by normal pulse; Causes: low potassium, stress, caffeine, heart disease; Effects/Symptoms: can lead to flutter or fibrillation, reduces effective blood flow if frequent~

What is atrial fibrillation (A. Fib)?

Disorganized, rapid depolarization of atrial tissue causing atria to quiver instead of contract; Atrial rate often >300 bpm, irregular ventricular rhythm, no identifiable P waves; Causes: heart disease, alcohol, caffeine, electrolyte imbalances; Effects/Symptoms: inefficient ventricular contraction → possible heart failure, blood pooling → ↑ risk for thrombosis/clots~

What is atrial flutter?

Rapid but organized atrial rhythm due to reentry circuit activity; Atrial rate 250–350 bpm, “sawtooth” pattern on EKG, ventricular response may be regular or irregular; Causes: heart disease, similar to A. Fib; Effects/Symptoms: risk for heart failure and thrombosis~

What is ventricular fibrillation (V. Fib)?

Chaotic, disorganized electrical activity in ventricles → no effective contraction; No distinct waveforms, no pulse, no cardiac output; Causes: myocardial ischemia or damage; Effects/Symptoms: life-threatening emergency, patient pulseless and unconscious, requires immediate defibrillation~

What are heart blocks (atrioventricular conduction disorders)?

Disorders of impulse conduction through AV node; Types include: First-degree (delayed conduction, all impulses reach ventricles, prolonged PR interval, usually asymptomatic), Second-degree Type I (Wenckebach, progressive PR lengthening until QRS dropped, often mild), Second-degree Type II (some P waves not followed by QRS, slower ventricular rate, ↓ pulse & cardiac output, dizziness), Third-degree/Complete (atria & ventricles beat independently, slow ventricular rate, ↓ cardiac output, can cause fainting)~

What is first-degree heart block?

Impulse conduction through AV junction is delayed but all impulses reach ventricles; Prolonged PR interval on EKG; Rhythm regular; Usually asymptomatic~

What is second-degree heart block Type I (Wenckebach)?

Progressively greater delay in AV conduction until one impulse is blocked; PR interval gets longer with each beat until one QRS dropped; Repeating pattern; Often mild or no symptoms~

What is second-degree heart block Type II?

Intermittent failure of some atrial impulses to conduct through AV node; Some P waves not followed by QRS complexes; Ventricular rate slower than atrial rate; Effects/Symptoms: ↓ pulse & cardiac output, dizziness, lightheadedness, fainting~

What is third-degree (complete) heart block?

Complete blockage of atrial impulses → atria & ventricles beat independently; No relationship between P waves & QRS, slow ventricular rate; Causes: MI, heart disease, drug/electrolyte disturbances; Effects/Symptoms: ↓ heart rate, ↓ cardiac output, ↓ pulse, severe dizziness/fainting~

What is asystole (ventricular standstill)?

Absence of any cardiac electrical activity → no rhythm, no heartbeat; Flat line on EKG, no pulse or cardiac output; Causes: end-stage heart disease, severe acidosis, hyperkalemia; Prognosis poor without immediate intervention~