- Define and Identify the following:
- Sinus rhythm
- Sinus bradycardia
- Sinus tachycardia
- Sinus arrhythmia
- Correctly measure the heart rate in any regular rhythm.
- Correctly measure the heart rate in atrial fibrillation.
- Define the pathophysiology of Sinus tachycardia Sinus bradycardia.
- List possible underlying causes of Sinus tachycardia Sinus bradycardia.
- Describe findings on physical examination or laboratory testing that would clarify the etiology.
The EKG provides a skilled reader with a wealth of information about the heart. One of the most basic yet important pieces of information the EKG provides is the heart rate (HR).
- The heart rate is defined as the number of times the heart beats per minute.
- It is a vital sign.
- It is always clinically relevant.
Calculating the heart rate is easy because the EKG is always recorded on graph paper that measures time as it travels horizontally through the machine. Ignoring the heart rate on an EKG is the single most common mistake in learning to read an EKG!
The Sinus Node: Master and Servant
The sinus node normally sets and controls the rate of depolarization and contraction of the rest of the heart. In this sense, the sinus node is the master of the heart. Yet, the sinus node is itself under the control of two parts of the nervous system—the sympathetic and parasympathetic nervous systems. These two forces are always active, with either one able to predominate depending on the clinical situation.
critical concept
Sinus Tachycardia:Pathophysiology
Sinus tachycardia represents a relative imbalance in the normal sympathetic/parasympathetic balance of the heart. There are two basic causes of sinus tachycardia:
- Increased sympathetic activity
- Decreased parasympathetic activity.
Increased sympathetic activity is by far more common clinically. Increased sympathetic activity is part of the ancient “flight or fight” protective emergency system of the body. It is analogous to someone inside the patient’s body calling a “code” or pulling a fire alarm. It is that serious, and that significant. The underlying cause should always be determined. It will typically be very relevant clinically.
Causes of increased sympathetic activity include:
- Shock.
- Heart failure.
- Infection.
- Bleeding.
- Pain.
- Pulmonary embolism.
- Hypoxia.
- Hypoglycemia.
- Anxiety.
- Drugs.
All are major disorders. Commonly used drugs that cause increased sympathetic activity include bronchodilators, inotropic infusions, and pressors. From the EKG, diagnose sinus tachycardia, and then evaluate the patient to determine its cause. Decreased parasympathetic activity is a much less common cause of sinus tachycardia and is most commonly related to atropine administration or poison ingestion. The most common big mistake EKG readers make is ignoring the presence of sinus tachycardia. A return to the bedside frequently provides the answer!
