Conduction Physiology
This conduction structure is specifically designed with switchbacks and multiple changes in direction to intentionally slow electrical propagation.
Answer: What is the AV node?
The SA node suppresses lower pacemakers because it possesses this unique characteristic.
Answer: What is the lowest automaticity threshold (fastest intrinsic firing rate)?
Mechanical systole begins during this portion of the EKG.
Answer: What is the ST segment?
The AV node lies within this anatomical triangle.
Answer: What is the Triangle of Koch?
An EKG demonstrates a PR interval of 0.10 seconds. According to the lecture, this interval is considered:
Answer: What is abnormally short?
Without this fibrous structure, atrial impulses could bypass the AV node and depolarize the ventricles directly.
Answer: What is the fibrous cardiac skeleton?
Immediately after ventricular depolarization, what happens to the automaticity timers throughout the myocardium?
Answer: They are reset simultaneously.
The atria repolarize during this electrical event, making atrial repolarization normally invisible.
Answer: What is the QRS complex?
Name all three borders of the Triangle of Koch.
Answer: What are the coronary sinus, septal leaflet of the tricuspid valve, and interatrial septum?
An EKG has a heart rate of 92 bpm, regular rhythm, PR interval of 0.16 sec, QRS duration of 0.09 sec, and a 1:1 P:QRS ratio. Identify the rhythm.
Answer: What is normal sinus rhythm?
If the Bundle of His is completely interrupted, what intrinsic pacemaker tissue would most likely maintain ventricular contraction?
Answer: What are the Purkinje fibers (ventricular pacemakers)?
Besides pacemaker cells, what other cardiac cells possess automaticity?
Answer: What are mechanical (myocardial) cells?
Which electrical event immediately precedes isovolumic contraction?
Answer: What is ventricular depolarization (QRS complex)?
This fascicle courses toward the inferior and posterior left ventricle.
Answer: What is the left posterior fascicle?
An EKG has a heart rate of 48 bpm, normal PR interval, narrow QRS, and a 1:1 P:QRS ratio. Identify the rhythm.
Answer: What is sinus bradycardia?
A depolarization begins in the SA node but cannot travel through the anterior internodal tract. Which remaining pathways still conduct the impulse to the AV node?
Answer: What are the middle and posterior internodal tracts?
Which myocardial property would be most directly affected if intercalated discs suddenly failed?
Answer: What is conductivity?
A patient demonstrates ventricular depolarization but no preceding atrial depolarization. Which EKG wave is absent?
Answer: What is the P wave?
This fascicle wraps around the apex before traveling basally along the anterior LV wall.
Answer: What is the left anterior fascicle?
An EKG has a heart rate of 132 bpm, normal PR interval, narrow QRS, and every QRS is preceded by a P wave. Identify the rhythm.
Answer: What is sinus tachycardia?
Name every structure an impulse must travel through to depolarize the anterior wall of the left ventricle.
Answer: What is SA node → internodal tracts → AV node → Bundle of His → Left Bundle Branch → Left Anterior Fascicle → Purkinje fibers?
A ventricular myocyte experiences increased intracellular calcium binding to troponin. Which myocardial property is directly enhanced?
Answer: What is contractility?
Name every electrical component occurring between the onset of atrial depolarization and the onset of ventricular repolarization.
Answer: What are the P wave, PR segment, PR interval, QRS complex, and ST segment?
This conduction pathway allows the left atrium to depolarize nearly simultaneously with the right atrium.
Answer: What is Bachmann's Bundle?
A rhythm has a heart rate of 88 bpm but demonstrates a PR interval of 0.28 seconds. Does this meet the criteria for normal sinus rhythm?
Answer: No. Although the rate and rhythm are sinus, the PR interval is prolonged (>0.20 sec), so it does not meet the criteria for normal sinus rhythm as defined in the lecture.