Which rhythm has a slow rate that can cause signs or symptoms of low cardiac output?

Which rhythm has a slow rate that can cause signs or symptoms of low cardiac output?

• A. First Degree Heart Block
• B. Second Degree Heart Block Type I
• C. Second Degree Heart Block Type II
• D. Junctional Escape Rhythm

Answer: (B)

The key idea is that a slow ventricular rate can reduce cardiac output enough to produce symptoms like dizziness or fatigue. In this rhythm, the PR interval progressively lengthens from beat to beat until a beat is dropped (a Wenckebach pattern). That intermittent loss of ventricular beats lowers the overall heart rate, which can compromise stroke volume and output, especially if the patient has limited compensatory reserve or ongoing factors like ischemia or AV-nodal–blocking drugs. Because the rate is intermittently slowed due to AV nodal conduction delay, symptoms from bradycardia are more likely. Other patterns either keep all beats conducted with a longer PR but normal rhythm, or produce abrupt dropped beats without the gradual PR lengthening, or reflect a separate slow escape rhythm from the AV junction. Among these, the gradual slowing with occasional failures to conduct best explains slow rate causing signs of low cardiac output.

The key idea is that a slow ventricular rate can reduce cardiac output enough to produce symptoms like dizziness or fatigue. In this rhythm, the PR interval progressively lengthens from beat to beat until a beat is dropped (a Wenckebach pattern). That intermittent loss of ventricular beats lowers the overall heart rate, which can compromise stroke volume and output, especially if the patient has limited compensatory reserve or ongoing factors like ischemia or AV-nodal–blocking drugs. Because the rate is intermittently slowed due to AV nodal conduction delay, symptoms from bradycardia are more likely. Other patterns either keep all beats conducted with a longer PR but normal rhythm, or produce abrupt dropped beats without the gradual PR lengthening, or reflect a separate slow escape rhythm from the AV junction. Among these, the gradual slowing with occasional failures to conduct best explains slow rate causing signs of low cardiac output.