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Physiology II
Cardiovascular Case B

complete atrioventricular block 

the patient: a 41-year-old woman

chief complaint: The woman was admitted while undergoing cardiopulmonary resuscitation. She had been found unconscious on the floor of her office at her place of work. No pulse or respirations had been detected; cardiopulmonary resuscitation was begun and was continued while en route to the hospital and in the emergency room. However, she could not be resuscitated and was pronounced dead. 

history: At the age of ten years, the patient had been noted to have a heart murmur and "skipped beats". There was no history of rheumatic fever or diphtheria, which may have damaged the valves or the conduction system of the heart. The pulse rate was 65 beats/min and the arterial pressure was 115/60 mm Hg. The ECG showed a normal atrial rhythm of 78 beats/min with a second-degree atrioventricular block (Wenckebach phenomenon). The second heart sound was loud, and a systolic murmur was heard. The heart appeared normal on a chest radiograph. 

Periodic re-examination revealed persistence of the systolic murmur and a ratio of atrial to ventricular beats as high as 2:1. At the age of 16 years, her resting pulse was found to be 44 beats/min, increasing to 58 beats/min during exercise. Her blood pressure was 1 10/85 mm Hg, and a systolic murmur was heard. The ECG revealed a complete heart block with an atrial rate of 95 beats/min and a ventricular rate of 44 beats/min at rest. At age 35, her arterial pressure was 185/70 and the pulse rate was 41 beats/min. An echocardiogram showed that the cardiac valves were normal, and the left ventricular ejection fraction was greater than normal. The ECG showed that the complete heart block persisted. At age 41 she collapsed and died. At autopsy, a benign mesothelioma was discovered which had completely replaced the atrioventricular node.


1. What is the significance of the difference between the pulse rate measured at the wrist and the atrial rate determined from the electrocardiographic tracing?  If you see it on the ECG but you don't feel it at the wrist then it means that that pulse was not perfused to the body.  Only the ones that you can feel are beats where blood flows.

2. What is a second-degree heart block? A third-degree heart block?  2nd degree is when the electrical flow is slowed down at the AV junction.  3rd degree is when there is a "complete heart block" at the AV junction.  The SA node fires as normal but no impulse from the SA node will reach the ventricles.  The ventricles will use either the perkinje fibers or the ventricular muscle as its pacer.

3. What is the significance of the increased left ventricutar ejection fraction?  Even though the heart was beating so slow, it still needed its normal output to appease the tissues, so, the left side of the heart became bigger and stronger so it could push out more blood with every heartbeat.

4. During the months preceding her death, what portion of the cardiac conduction system was most likely serving as the cardiac pacemaker?  The heart probably had been using the perkinje fibers for some time and prior to her death she may have started using her ventricular muscle (evident in the slowing down even further of her heart).

5. What can you conclude regarding her resting stroke volume during the months immediately preceding her death?  Do the the question above, her heart was beating stronger to keep up the CO.  The heart was beating very slow too.  This means that there was a very high arterial systolic pressure and do to the longer than usual time inbetween beats, the diastolic pressure would be quite low .. so that means that the pulse pressure would be very high.  PP = SBP - DBP

6. What was the most likely cause of her murmur?  The rushing of blood out of the aorta during systole.


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