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2. A. Sinus bradycardia. Each cycle commences with a P wave and the PR interval is normal. Therefore, rhythms are sinus paced and differ only in rate: normal sinus rhythm, sinus bradycardia, or sinus tachycardia. In this case, it is sinus bradycardia, because the rate is 60. B. Junctional rhythm. There are no P waves and a PR interval cannot be ascertained. Therefore, the sinoatrial node is not pacing this rhythm. But the QRS complexes are narrow, so the pacemaker is above the ventricles. The logical conclusion is that the atrioventricular node or neighboring tissue is pacing the heart. This is called junctional rhythm. Because this node has a slower firing rate than the sinoatrial node (See Figure 1), rates of 50 and 90 are the cutoffs for bradycardic and tachycardic rates, ie, junctional bradycardia or tachycardia. C. Normal sinus rhythm with second-degree (Mobitz) atrioventricular block. Each cycle commences with a P wave, but occasionally the P wave is not followed by a QRS and another P wave appears. This is called a "dropped beat" and is the fundamental defect in a second-degree or Mobitz block. Notice that all PR intervals are identical. They may be normal in length or delayed, but they are all the same; even after a beat is dropped, they resume their duration. This is called a Mobitz 2 block. In this particular example, the ratio of P waves to QRS complexes is 2 1. Therefore, the R-R intervals are regular. With any other ratio, eg, 3: 1 or 4: 1, the R-R interval would appear irregular. D. Atrial flutter. Multiple waves appear between each QRS complex and we cannot ascertain whether they are P or T waves. This pattern emerges when an ectopic pacemaker emerges in the atrial muscle and fires more rapidly than the sinoatrial node. This generates multiple depolarizations in the atrial muscle, reflected as so-called flutter waves. Each has a slant to its anterior portion; we can describe this as a saw-toothed pattern. Normally, the atrioventricular node allows only one of them to pass into the ventricle each cycle, which results in a regular ventricular response.

2. A. Sinus bradycardia. Each cycle commences with a P wave and the PR interval is normal. Therefore, rhythms are sinus paced and differ only in rate: normal sinus rhythm, sinus bradycardia, or sinus tachycardia. In this case, it is sinus bradycardia, because the rate is 60. B. Junctional rhythm. There are no P waves and a PR interval cannot be ascertained. Therefore, the sinoatrial node is not pacing this rhythm. But the QRS complexes are narrow, so the pacemaker is above the ventricles. The logical conclusion is that the atrioventricular node or neighboring tissue is pacing the heart. This is called junctional rhythm. Because this node has a slower firing rate than the sinoatrial node (See Figure 1), rates of 50 and 90 are the cutoffs for bradycardic and tachycardic rates, ie, junctional bradycardia or tachycardia. C. Normal sinus rhythm with second-degree (Mobitz) atrioventricular block. Each cycle commences with a P wave, but occasionally the P wave is not followed by a QRS and another P wave appears. This is called a "dropped beat" and is the fundamental defect in a second-degree or Mobitz block. Notice that all PR intervals are identical. They may be normal in length or delayed, but they are all the same; even after a beat is dropped, they resume their duration. This is called a Mobitz 2 block. In this particular example, the ratio of P waves to QRS complexes is 2 1. Therefore, the R-R intervals are regular. With any other ratio, eg, 3: 1 or 4: 1, the R-R interval would appear irregular. D. Atrial flutter. Multiple waves appear between each QRS complex and we cannot ascertain whether they are P or T waves. This pattern emerges when an ectopic pacemaker emerges in the atrial muscle and fires more rapidly than the sinoatrial node. This generates multiple depolarizations in the atrial muscle, reflected as so-called flutter waves. Each has a slant to its anterior portion; we can describe this as a saw-toothed pattern. Normally, the atrioventricular node allows only one of them to pass into the ventricle each cycle, which results in a regular ventricular response.

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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A. Sinus bradycardia. Each cycle commences with a P wave and the PR interval is normal. Therefore, rhythms are sinus paced and differ only in rate: normal sinus rhythm, sinus bradycardia, or sinus tachycardia. In this case, it is sinus bradycardia, because the rate is 60. B. Junctional rhythm. There are no P waves and a PR interval cannot be ascertained. Therefore, the sinoatrial node is not pacing this rhythm. But the QRS complexes are narrow, so the pacemaker is above the ventricles. The logical conclusion is that the atrioventricular node or neighboring tissue is pacing the heart. This is called junctional rhythm. Because this node has a slower firing rate than the sinoatrial node (See Figure 1), rates of 50 and 90 are the cutoffs for bradycardic and tachycardic rates, ie, junctional bradycardia or tachycardia. C. Normal sinus rhythm with second-degree (Mobitz) atrioventricular block. Each cycle commences with a P wave, but occasionally the P wave is not followed by a QRS and another P wave appears. This is called a "dropped beat" and is the fundamental defect in a second-degree or Mobitz block. Notice that all PR intervals are identical. They may be normal in length or delayed, but they are all the same; even after a beat is dropped, they resume their duration. This is called a Mobitz 2 block. In this particular example, the ratio of P waves to QRS complexes is 2 1. Therefore, the R-R intervals are regular. With any other ratio, eg, 3: 1 or 4: 1, the R-R interval would appear irregular. D. Atrial flutter. Multiple waves appear between each QRS complex and we cannot ascertain whether they are P or T waves. This pattern emerges when an ectopic pacemaker emerges in the atrial muscle and fires more rapidly than the sinoatrial node. This generates multiple depolarizations in the atrial muscle, reflected as so-called flutter waves. Each has a slant to its anterior portion; we can describe this as a saw-toothed pattern. Normally, the atrioventricular node allows only one of them to pass into the ventricle each cycle, which results in a regular ventricular response.
Transcribed Image Text:A. Sinus bradycardia. Each cycle commences with a P wave and the PR interval is normal. Therefore, rhythms are sinus paced and differ only in rate: normal sinus rhythm, sinus bradycardia, or sinus tachycardia. In this case, it is sinus bradycardia, because the rate is 60. B. Junctional rhythm. There are no P waves and a PR interval cannot be ascertained. Therefore, the sinoatrial node is not pacing this rhythm. But the QRS complexes are narrow, so the pacemaker is above the ventricles. The logical conclusion is that the atrioventricular node or neighboring tissue is pacing the heart. This is called junctional rhythm. Because this node has a slower firing rate than the sinoatrial node (See Figure 1), rates of 50 and 90 are the cutoffs for bradycardic and tachycardic rates, ie, junctional bradycardia or tachycardia. C. Normal sinus rhythm with second-degree (Mobitz) atrioventricular block. Each cycle commences with a P wave, but occasionally the P wave is not followed by a QRS and another P wave appears. This is called a "dropped beat" and is the fundamental defect in a second-degree or Mobitz block. Notice that all PR intervals are identical. They may be normal in length or delayed, but they are all the same; even after a beat is dropped, they resume their duration. This is called a Mobitz 2 block. In this particular example, the ratio of P waves to QRS complexes is 2 1. Therefore, the R-R intervals are regular. With any other ratio, eg, 3: 1 or 4: 1, the R-R interval would appear irregular. D. Atrial flutter. Multiple waves appear between each QRS complex and we cannot ascertain whether they are P or T waves. This pattern emerges when an ectopic pacemaker emerges in the atrial muscle and fires more rapidly than the sinoatrial node. This generates multiple depolarizations in the atrial muscle, reflected as so-called flutter waves. Each has a slant to its anterior portion; we can describe this as a saw-toothed pattern. Normally, the atrioventricular node allows only one of them to pass into the ventricle each cycle, which results in a regular ventricular response.
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