Basic ECG Rhythm Recognition for Nurses

The continual beep-beep-beep of ECG machines forms the auditory backdrop of many healthcare environments. ECG rhythm recognition and interpretation is an essential skill for nurses practicing in areas where patients are cardiac monitored. They should also be able to identify ECG patterns that warrant immediate interventions.

Related: Basic ECG Recognition and Interpretation, 2nd edition

Basic ECG rhythm recognition: Types of ECG machines

While there are many variations, these are some of the main types of ECG machines:

Hard-wired bedside monitor
Telemetry monitor
12-lead ECG machine
Combination monitor, 12-lead, pacemaker, and defibrillator (usually portable)
Continuously worn event monitors, such as Holter monitors

Although designed for continuous use, there are some limitations to the information these monitors can provide. The 12-lead machines offer perhaps the most detail, with information recorded in 10-second intervals.

Some slight variations in ECG rhythms are normal; others require closer attention, and possible intervention. Here are some common abnormal rhythms and what they might mean.

Sinus tachycardia

A sinus rhythm faster than 100 bpm is called sinus tachycardia. Sinus tachycardia is usually a normal physiologic reaction to the body’s need for increased cardiac output. For example, a sudden fright causes release of adrenaline, and the sinus node responds by speeding up. The cause of sinus tachycardia can usually be discovered simply by assessing the patient.

Some possible causes of sinus tachycardia:

Fear and anxiety
Fever
Pain
Hypovolemia (dehydration or bleeding)
Hypoxia
Drug effects

Sinus bradycardia

When a rhythm meets all criteria for sinus rhythm, but the rate is below 60 bpm, it is called sinus bradycardia. Sinus bradycardia is often a normal finding, but it can be problematic for the patient if the rate is too slow to maintain adequate cardiac output. When sinus bradycardia results in hemodynamic instability and poor tissue perfusion, intervention is necessary.

Some possible causes of sinus bradycardia:

Medications used to lower rate or blood pressure, including calcium channel inhibitors, beta blockers, and digitalis
Hypoxia
Acidosis
Hyperkalemia or hypothermia
Increased vagal tone, such as that seen in young, fit, healthy people or when a person is gagging or vomiting
Trauma: tension pneumothorax, cardiac tamponade

Sinus arrhythmia

A normal sinus rhythm or sinus bradycardia that shows a fluctuation in rate along with the patient’s breathing is called sinus arrhythmia, or sometimes respiratory sinus arrhythmia (RSA).

RSA is considered a normal variant, especially in young, healthy people. The heart rate will increase slightly during inspiration and decrease to normal baseline on expiration. This can reflect the increased vagal tone of the healthy athletic person. It may also be a physiologic phenomenon that saves energy by speeding the heart rate during time of peak perfusion of the lungs and slowing it during expiration and less perfusion

Atrial tachycardia

A fast, regular rhythm, usually between the rates of 150 bpm and 250 bpm, but always over 100 bpm, is called atrial tachycardia. There are several different mechanisms that can cause atrial tachycardia, and there are many names associated with them. Atrial tachycardia is one of the supraventricular tachycardias, which means tachycardia coming from above the ventricles, but not from the sinus node.

Sometimes atrial tachycardia is caused by a rapidly firing pacemaker influenced by increased automaticity. More often, it is caused by one premature atrial contraction (PAC) getting caught in a re-entry loop.

Re-entry results in a sudden onset of tachycardia and then a sudden offset, either spontaneously or with medical treatment. This is called paroxysmal supraventricular tachycardia (PSVT). PSVT rhythms warrant close observation to determine if they are persistent and require treatment.

Recognizing atrial tachycardia:

The rate is over 100 bpm, most often 150 to 250 bpm
P waves are present but may be “buried” in preceding T waves
P waves have different morphology than sinus P waves
The rhythm is regular and usually starts and stops suddenly
QRS complexes are narrow unless affected by a separate conduction delay in the ventricles

Atrial flutter

Another supraventricular tachycardia that results from a re-entry circuit in the atria is atrial flutter. Typically, in atrial flutter, the atrial rate is 250 bpm to 350 bpm, but it can be 130–400 bpm. When a clinician views leads with prominent P waves, called flutter (F) waves, the baseline can look like a sawtooth pattern.

A quick way to recognize atrial flutter is to identify one F wave for every large box on the ECG paper. That indicates an atrial rate of 300 bpm.

Recognizing atrial flutter:

A regular atrial rhythm with a rate of approximately 250–350 bpm
Flutter waves, especially visible in leads II, III, and aVF. No isoelectric (flat) baseline
Narrow QRS complexes that are all alike
P to QRS conduction ratio may be 1:1 (rare); 2:1 (common); 3:1, 4:1, or greater

Atrial fibrillation

Atrial fibrillation (AFib) is another supraventricular tachycardia, like atrial tachycardia and atrial flutter. Experts do not yet completely understand the exact mechanisms of AFib. Multiple pacemakers, or multiple re-entry circuits, produce hundreds of uncoordinated waves that are unable to depolarize the atria in a synchronized way. Instead, each focus depolarizes a small amount of tissue, resulting in the atria quivering. This quivering prevents the atria from contracting and pumping blood into the ventricles.

The patient experiences a loss of “atrial kick,” which is a large part of the preload of the ventricles. Loss of atrial kick can lower cardiac output by up to 20% to 30%.

Classifications of AFib:

Paroxysmal AFib spontaneously returns to a normal rhythm within 7 days
Persistent AFib lasts longer than 7 days
Permanent AFib lasts longer than 12 months

Practicing ECG rhythm recognition and interpretation

Clinicians can enhance their fluency and confidence in ECG rhythm recognition and interpretation by developing a system for reading each rhythm strip. Here’s a sample of a systematic approach to rhythm interpretation.

Assess the strip for artifact: If there is too much artifact to accurately read the strip, correct the problem and obtain another strip.
Calculate rate: Correlate the rate with the patient’s hemodynamic status. Is immediate action needed?
Assess the rhythm: Is the rhythm regular, regularly irregular, or irregularly irregular?
Assess the width of the QRS: Wide QRS can mean a ventricular rhythm or an intraventricular conduction delay.
Assess the P waves and PR intervals: Are the P waves regular? Do they all look alike? Are the PR intervals within normal limits and all the same? Do the P waves precede the QRS complexes?
Determine the name of the rhythm: What is your first impression? If the ECG criteria of that educated guess do not match what you see, try again.
Obtain assistance if necessary: Notify the patient’s primary care provider, other members of the health care team, or resuscitation team if the patient’s cardiac rhythm requires intervention beyond what is already ordered.