Sinus Rhythm | Sinus Bradycardia | Sinus Tachycardia

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Authors and Reviewers

Authored by Thomas O'Brien.
Medically reviewed by Dr. Jonathan Keroes, MD, Cardiology.
Last Update: 2/4/2022

Introduction

• The five-steps of rhythm analysis must be followed regardless of how simple of complex the tracing is you are reviewing.
• The information gathered in these steps are telling a story.
• The title of that story is the interpretation.

Sinus Rhythm Types

The dysrhythmias in this category occur as a result of influences on the Sinoatrial (SA) node. Rhythms in this category will share similarities in a normal appearing P wave, the PR interval will measure in the “normal range” of 0.12 – 0.20 second, and the QRS typically will measure in the “normal range” of 0.06 – 0.10 second. For the most part, dysrhythmias in this category either effect the rate, rhythm regularity or both within a particular tracing. We will be discussing the following complexes and rhythms:

• Normal Sinus Rhythm
• Sinus Bradycardia
• Sinus Tachycardia
• Sinus Dysrhythmia (Arrhythmia)
• Sinus Arrest
• Sinus Exit Block

Introduction

• Also known as Sinus Rhythm is the only rhythm when each of the five steps of rhythm analysis are “normal”.
• All other rhythms you will analyze will have at least one of the 5-steps presenting an abnormality.
• This rhythm will be regular, in a heart rate range between 60 – 100 bpm, P waves are upright and uniform in appearance (in Lead II), with a P wave for each QRS complex, the PR interval will measure in the normal range of 0.12 – 0.20 second (and measure the same each time), and the QRS complex morphology will be similar beat-to-beat and measure between 0.06 – 0.10 second (and measure the same each time).

Practice Strip

Analyze this tracing.

Description

• Rhythms are often named according to the origin of the electrical activity in the heart or the structure where the problem is occurring.
• Sinus Rhythms are aptly named due to the locus of stimulation being the SA (sinoatrial) node.
• With Sinus Bradycardia the locus of stimulation is the same as normal sinus rhythm, just now the rate will be less than 60 bpm. Recall that “brady” means slow.
• The only difference between sinus bradycardia and normal sinus rhythm is the rate. All other steps in the rhythm analysis are “normal”.

Practice Strip

• Analyze this tracing using the five steps of rhythm analysis.
• Compare your answers with the answers on the next slide.

Description

• Sinus Tachycardia occurs when the rate of electrical impulse formation occurs at a rate exceeding 100 bpm.
• This can occur for a number of different reasons i.e. diet, stress, illness, response to physical exertion etc.
• The only difference between Normal Sinus Rhythm and Sinus Tachycardia is the rate exceeds 100 bpm. All other steps of rhythm analysis will be “normal.
• An additional challenge that will present as rhythm rates accelerate is that the cardiac complexes will come closer together. This can result in the P wave becoming partially or completely buried within the T wave of the previous cardiac complex.
• The result of a partially buried P waves means you are unable to establish the beginning of atrial depolarization. Meaning you will be unable to measure and report the PR interval. The only way it will be possible is if the physician instructs you to increase the machine printing speed (remember interval times will double at 50 mm/sec).

Practice Strip

Analyze this tracing using the five steps of rhythm analysis.

Description

• Sinus Dysrhythmia often occurs as a normal variant. It is commonly seen in young healthy people and athletes. It is frequently related to breathing and pressure on the vagus nerve. As the patient inhales and the lungs expand, pressure is applied to the vagus nerve which causes a parasympathetic response and a decrease in heart rate.
• Sinus Dysrhythmias may also occur as a result of medication effects or diseases such as multiple sclerosis.
• This dysrhythmia often requires no treatment, but may require medication or therapy such as a pacemaker to regulate the heart rate if the ventricular response becomes too slow.
• Sinus Dysrhythmia closely resembles Normal Sinus Rhythm with the only distinction being the intervals from one cardiac complex to the next are changing as influenced by the patients respiratory pattern.
• Note the changing R to R Intervals.

Practice Strip

Analyze this tracing using the five steps of rhythm analysis.

Description

• Sinus Arrest occurs when there is a sudden absence of electrical activity initiated by the SA node. This results in a pause in the electrical activity seen on the tracing. Remember, no electrical activity = no depolarization and contraction. Hence, a drop in blood pressure.
• The longer the pause, the further the blood pressure will drop.
• A pause of six-seconds is considered a medical emergency and emergency procedures must be initiated.
• The rhythm typically will demonstrate constant R to R intervals prior to and following the pause. This pause results in the rhythm tracing presenting as irregular.

Analysis

• It is important to measure the duration of the pause and report this information along with the frequency of the pauses if there are more than one.
• The pause is measured by placing your caliper tips on the last R wave just prior to the pause and the R wave immediately following the pause. Count the number of small boxes and multiply by 0.04 second. This will be reported as part of the interpretation.

Practice Strip

Analyze this tracing using the five steps of rhythm analysis.

Description

• Sinus Exit Block looks very much the same as Sinus Arrest with one important distinction.
• The duration of the pause with Sinus Exit Block is in a direct multiple of the R to R interval of the underlying rhythm. Sinus Arrest does not have this specific feature.

Practice Strip

Analyze this tracing using the five steps of rhythm analysis.