Pearls of Knowledge: Reentry

Interpreting Rhythms: Reentry 

Pearls of Knowledge          ©

Reentry is one of the most common causes of supraventricular and ventricular rhythms. It is seen with atrial fibrillation, atrial flutter, and runs of beats such as in ventricular tachycardia or paroxysmal atrial tachycardia. 

Typically, the myocardial tissue is depolarized and then becomes refractory. In patients with structural  heart  disease,  or  scar  tissue  from ischemia or infarction, a change in conduction occurs in some of the myocardial tissue and the tissue is not depolarized at the same time. Reentry occurs when a portion of the tissue is reactivated by an impulse that had already stimulated it. 

Local reentry

 Local reentry occurs within a small area (single site) of the atrium or ventricle such as atrial flutter, ventricular tachycardia, or paroxysmal atrial tachycardia. In atrial...

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Pearls of Knowledge: AV Dissociation

Dysrhythmias: AV Dissociation 

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AV dissociation occurs when there are two pacemakers present in the heart, usually for a relatively short period of time. The rate of the atria and ventricles will be very similar, but they are not “married”. The rhythm is easy to mistake for third-degree heart block. 

Generally, the P waves will appear to “fade” into the QRS complexes and come out the back.

Rhythm analysis

(The P waves fade into the QRS and come out the back. The P waves are caused by the SA node. The QRS complexes are coming from the AV junction since the QRS is a normal duration.)


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Pearls of Knowledge: Detecting Murmurs

Advanced Heart Sounds: Detecting Murmurs

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To elevate clinical practice, health care professionals should be listening to all four areas of the heart valves during an assessment. 

In acute conditions, listening to heart sound is very important on presentation and then with subsequent assessments. If heart sounds change, it generally signifies a deterioration in condition such as ischemia or infarction (especially with inferior wall), or rupture of a papillary muscle, or the perforation of the intraventricular septum due to scar tissue.

Four areas of the valves to listen to:

  • Aortic: 2nd ICS, right sternal border
  • Pulmonic: 2nd ICS, left sternal border
  • Tricuspid: 4th ICS, left sternal border
  • Mitral: 5th ICS, left midclavicular line under the breast

Murmurs may be innocent or benign, all of which will be systolic murmurs.

  • Innocent murmurs are heard in children, adolescents,...
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Pearls of Knowledge: Anemia and Hydration

Lab Values: Anemia and Hydration 

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The CBC with differential is a frequently ordered lab test and provides much information regarding infection, anemia, coagulation, and hydration. When bone marrow suppression occurs, low levels of red blood cells, white blood cells, and platelets will be seen. 

Monitoring anemia 

Anemia is seen frequently in many different types of patients. When the red blood cells are low, pallor will be seen. If the red blood cells are too numerous, such as in polycythemia vera, the blood is “thicker” and there is a risk for blood clotting and myocardial dysfunction due to the strain.

Men have a higher red blood cell count mostly due to hormonal differences which stimulate higher hemoglobin production and greater muscle mass. For ease in clinical practice, it is helpful to remember the normal level for hemoglobin for everyone is...

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Pearls of Knowledge: Junctional Rhythms

Dysrhythmias: Junctional rhythms 

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In junctional rhythm, the SA node is no longer in control and the AV node becomes the pacemaker by default due to the property of automaticity. Because the AV node is a less reliable pacemaker, the development of junctional rhythm is cause for concern. The analysis of junctional rhythms is determined by the P waves and the rate. 

Because the impulse starts in the AV node, the atria are depolarized in a retrograde manner resulting in an inverted P wave in the upright (positive) leads (such as lead II).

Analysis of inverted P waves (in the upright leads) 

  • Inverted P wave before the QRS when the atria depolarize before the ventricles. 
  • Inverted P wave buried in the QRS when the atria and ventricles depolarize at the same time. 
  • Inverted P wave after the QRS when the ventricles depolarize before the...
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Pearls of Knowledge: Second-degree AV Blocks

Dysrhythmias: Second-degree AV Blocks 

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A defect in the AV node causes sinus rhythm with second-degree AV block, type I. Transmission takes longer with each successive impulse until one fails to be conducted to the ventricles. The PR interval gets progressively longer until some sinus impulses are blocked by the AV node. The rhythm usually occurs in a cyclic pattern such as 3:2, 5:4, etc. It is usually a temporary disorder and does not necessitate a pacemaker because it is not progressive. 

A defect below the AV node in the Bundle of His or bundle branch system due to ischemia or injury causes second- degree AV block, type II. The sinus impulses are usually blocked at regular intervals, allowing only every second, third, or fourth impulse to be conducted to the ventricles. The PR intervals which are present will be constant. 2:1 conduction is common in second-degree,...

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Pearls of Knowledge: Friction Rubs

Assessment: Friction Rubs 

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Friction rubs are dry, cracking, and grating sounds caused by inflamed, roughened surfaces rubbing together. Due to the irritation in pericarditis and pleurisy, effusions will develop, and the friction rub will no longer be heard. The friction rub, heard early in the course, may be transient in both conditions and can cause significant pain. 

Pericardial friction rub

  • Heard during S1 and S2.
  • Heard during inhalation and exhalation.
  • Loudest at the apex and left sternal border.
  • Heard best in the left lateral position or when leaning forward.
  • Will be present in pericarditis and cardiac contusion.

Pleural friction rub

  • Heard only on inhalation.
  • Will be present in pleurisy and pulmonary embolus with pulmonary infarction. 


So, the next time you hear a “grating” sound in the chest during your assessment, have the patient...

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Pearls of Knowledge: SA Nodal Dysfunction

Advanced Dysrhythmias: SA Nodal Dysfunction 

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The SA node is composed of P cells. Blood supply is from the SA nodal artery which is easily damaged. When damaged, ischemia results, fibrosis develops, and the node becomes dysfunctional. Initially the dysfunction may produce only mild symptoms, depending on the rate and duration of pauses. In more advanced disease, dizziness and possible syncopal episodes may be seen.

Three types of SA nodal dysfunction are covered here. They include abnormal overdrive suppression, sinus arrest, and sick sinus rhythm. With sick sinus syndrome the problem may be in the SA node or in the AV node.

Overdrive Suppression 

In normal conduction, when an early beat occurs (such as a PAC), there is a pause in the rhythm. In healthy hearts, the conduction system “resets” itself and the rhythm resumes after the early beat....

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Pearls of Knowledge: WBC and the Differential

Lab Values: WBC and the Differential 

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There are many conditions that will alter the white blood cell count. The most common cause of an elevation is a bacterial or parasitic infection or any type of an inflammatory disorder. Some of the immune system and thyroid disorders may be implicated. Select drugs, such as glucocorticoids will also elevate the count. Leukemia will elevate the count; however, the cells are dysfunctional, and a risk for infection is present.

A low white blood cell count is often caused by viral infections, severe infections due to depletion of the cells, congenital disorders, damage to the bone marrow, autoimmune disorders, and medications such as anti-infectives or chemotherapy that suppress the bone marrow. Leukopenia is white blood cells < 1,000 cells/mm3. Agranulocytosis is a severe decrease of < 200 cells/mm3.

Types of white blood cells 


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Pearls of Knowledge: Torsades de pointes

Dysrhythmias: Torsades de Pointes

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Torsades de pointes is a life-threatening type of ventricular tachycardia that is associated with a prolonged QT interval. The QT interval is comprised of the absolute (ARP) and relative refractory (RRP) periods. During the absolute refractory period, no stimulus can cause an electrical response in the heart. During the relative refractory period, a strong stimulus can trigger a response, such as Torsades de pointes.

The prolongation of the QT interval may be due to a congenital defect but is most frequently caused by drug therapy (of which, there are many). A prolonged QT interval is also seen in electrolyte imbalances, particularly hypokalemia and hypomagnesemia. Treatment for Torsades de pointes is the administration of magnesium, even in the presence of a normal magnesium level. If pulseless, then defibrillation.

Measuring the QT Interval

The QT...

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