Disclaimer

If you are having severe symptoms including but not limited to chest pain, shortness of breath, or fainting, we recommend you call 911 (or your local emergency services). The explanations below are for informational purposes only and not designed for the treatment of emergencies.

 

Rhythms

ECG Basics Explanation Video

Normal sinus rhythm

Normal Sinus Rhythm Explaination Video

Explanation: This is the normal rhythm of your heart. The heartbeat starts in the sinus node, your heart’s built-in pacemaker. Electricity is conducted through the atrium (upper chambers) to the atrioventricular node. There is typically a short delay in the atrioventricular node before the electricity is conducted down into the ventricles (lower chambers).

Sinus bradycardia:

Explanation: This is a slow heart rate, defined as a heart rate less than 60 bpm. This rhythm is controlled by the heart’s normal electrical system. The heart’s normal pacemaker (the sinus node) is controlling this rate.  There are many reasons for a low heart rate. People often have a heart rate of less than 60 when resting or sleeping. The heart rate should be as high as it needs to be to support your body’s activity level. Medications can also reduce heart rate.

Symptoms: The majority of people with sinus bradycardia have no symptoms. Some people will develop fatigue and shortness of breath when the heart rate is lower than needed for any activity level

Treatment: Asymptomatic sinus bradycardia typically does not require any treatment. If the heart rate is consistently below 50 bpm OR symptoms are present then we recommend evaluation by a medical professional.

Sinus tachycardia:

Explanation: This is a fast heart rate, defined as a heart rate greater than 100 bpm. This rhythm is controlled by the heart’s normal electrical system. The heart’s normal pacemaker (the sinus node) is controlling this rate. There are many reasons for an elevated heart rate. It is normal and expected to have a heart rate greater than 100 when active, especially with strenuous exercise. The heart rate should be as high as it needs to be to support your body’s activity level. Stimulants (including caffeine), medications, and illness (i.e. flu, pneumonia, stress, dehydration, etc.) can also cause an elevated heart rate. Rarely people simply have an elevated resting heart rate.

Symptoms: The majority of people with sinus tachycardia have no symptoms. Generally, sinus tachycardia at rest is a symptom of an underlying condition, so any symptoms present are typically related to the underlying condition. Rarely people with chronically elevated heart rates, develop fatigue and palpitations.

Treatment: Sinus tachycardia with activity and exercise is expected. Sinus tachycardia at rest is usually secondary to another process and can typically be treated by fixing the underlying cause (ie. stress reduction, avoiding stimulants, treatment of illness, etc.). People with chronically elevated heart rates at rest should be evaluated by a medical professional to ensure there is no underlying heart disease that requires treatment.

Sinus Arrhythmia:

Explanation: This is an irregular heart rhythm. This rhythm is controlled by the heart’s normal electrical system. The heart’s normal pacemaker (the sinus node) is controlling this rate. This rate typically varies over time with activity. In people with sinus arrhythmia, the rate varies more than usual even at rest.

Symptoms: People with sinus arrhythmia typically have no symptoms.

Treatment: No treatment is required

Junctional Rhythm

Explanation: This is a rhythm that uses your heart’s normal conduction system, but is initiated from the AV node. The rate can vary from person to person. Occasionally sinus rhythm can be mistaken for a junctional rhythm, especially if the P waves on the ECG strip are very small.

Symptoms: Symptoms from a junctional rhythm typically depend on the heart rate. If the heart rate is in the normal range (60-100bpm), there will likely be no symptoms. If the heart rate is low (less than 60bpm) then common symptoms include fatigue, dizziness, and shortness of breath. If the heart rate is very low then symptoms can be severe.

Treatment: We recommend evaluation by a medical professional if you have a junctional rhythm. Junctional rhythms often require no treatment, however, if the heart rate is slow, or the rhythm is causing symptoms, then it may require intervention, ranging from medication changes to a pacemaker.

Wide complex Tachycardia

Explanation: This is a category of rhythm that may originate from the upper chambers or lower chambers. It represents a fast heart rate in the upper chambers that is conducted to the lower chambers with aberrancy, typically a bundle branch block (SVT with aberrancy), or a fast heart rhythm originating from the bottom chambers of the heart (ventricular tachycardia). It is often impossible to tell the difference between these two mechanisms on a single lead ECG.

Symptoms:

  • Ventricular Tachycardia (VT): VT can be fatal, symptoms are often severe including syncope (fainting), chest pain, fatigue, shortness of breath.
  • SVT with aberrancy: Symptoms of SVT with aberrancy are often less severe than VT, but can be severe depending on the heart rate. Symptoms are similar to SVT as detailed below

Treatment: It is usually impossible to tell the difference between VT and SVT with aberrancy on a single lead ECG, so wide complex tachycardia requires immediate evaluation by a medical professional.

Premature complexes

Premature atrial complex (PAC)

Explanation: Premature complexes (or Atrial premature complexes) are one of the most frequent causes of irregular heartbeats. Atrial premature complexes can be triggered from almost any part of the upper chambers. Although premature complexes commonly occur in normal hearts, they can be associated with structural heart disease. Premature complexes tend to increase with age.

Symptoms: Most people do not have symptoms with PAC, however occasionally they are symptomatic. Commonly people will describe skipped beats or pauses. This is related to the short pause that occurs following the extra beat, this usually occurs when the premature atrial complex is so close to the previous beat that it is not conducted into the ventricle.

Treatment: PACs generally do not cause cardiac problems, and generally do not require treatment. If symptomatic then these can usually be managed with medications and rarely with cardiac ablation.

Premature Ventricular Complex (PVC)

Explanation: Premature ventricular complexes (or ventricular premature complexes) are one of the most frequent causes of irregular heartbeats. PVCs can be triggered from almost any part of the lower heart chambers. Although premature complexes commonly occur in normal hearts, they can be associated with structural heart disease. Premature complexes tend to increase with age. Approximately 80% of apparently healthy people will have some PVCs in a 24 hour period.

Symptoms: Most people do not have symptoms with PVCs, however occasionally people are symptomatic. Commonly people will describe palpitations, skipped beats, or pauses. Rarely, PVCs can cause lightheadedness or syncope (fainting). Very frequent PVCs can cause fatigue and shortness of breath, especially with exercise.

Treatment: Occasional PVCs generally do not require treatment. Frequent PVCs can result in cardiomyopathy (weak heart) or heart failure over time. The definition of frequent is debated in the literature. We generally recommend further evaluation by a medical professional if you are symptomatic with PVCs or if PVCs comprise more than 10% of your heartbeats.

Supra-ventricular Tachycardia (SVT)

Supraventricular tachycardia is a category of fast heart rates, the most common of these are detailed below. It can be very difficult to distinguish between these types of fast heart rates on a single ECG, so often the interpretation will simply read SVT. We recommend further evaluation by a medical professional for all SVTs.

Atrial Tachycardia (AT)

Explanation: Atrial tachycardia is a fast heart rhythm that originates from the top chambers of the heart. Usually, the rate ranges from 150 – 200 bpm, but it can be slower. This rhythm can be seen in people with normal hearts, or with structural heart disease. Additionally, it can be triggered by certain medications. If atrial tachycardia persists over days to weeks, then it can cause cardiomyopathy (weak heart).

Atrial tachycardia is difficult to diagnose with a single lead ECG. It may be suggested by a heart rate that is higher than would be expected for a given activity level (i.e. heart rate of 160 bpm while sitting quietly on the couch), however, it can be mistaken for sinus tachycardia.

Symptoms: The most common symptoms are palpitations or fluttering. Rarely atrial tachycardias are associated with syncope (fainting). In people with underlying structural heart disease, AT is often associated with worsening of their underlying disease.

Treatment: People with underlying structural heart disease may require hospitalization to manage persistent atrial tachycardia. However, the majority of people with minimal or no symptoms can be monitored with clinic visits, managed with medications, or rarely considered for cardiac ablation. People with more severe symptoms can be managed with medications or considered for cardiac ablation.

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

Explanation: AVNRT is a regular fast heartbeat. A “short circuit” occurs in the heart electrical system, allowing the creation of an electrical loop in the area of the AV node. As electricity is quickly conducted around this loop, it drives the heart rate. This type of SVT is very common. It will often come and go, for many years before it is diagnosed. It can be misdiagnosed as panic attacks or anxiety.

Symptoms: The most common symptoms are palpitations, dizziness, and shortness of breath, that come and go. More severe symptoms including chest pain and syncope (fainting) are rare.

Treatment: AVNRT may cause palpitations and dizziness, but is generally not considered dangerous, except in rare instances where symptoms are severe. In the acute setting (while the heart is fast), many people find that they can stop the tachycardia using vagal maneuvers (bearing down, passive leg raises, etc.). If AVNRT continues, it will require an emergency room visit for treatment. Long term, AVNRT can be managed with medications or cardiac ablation.

Atrioventricular Reentrant Tachycardia (AVRT)

Explanation: AVRT is a regular fast heartbeat. An extra electrical connection is present in the heart, that has generally been present since birth. This extra connection between the top and bottom chambers of the heart allows for an electrical loop to be established. Electricity is quickly conducted around this loop, driving a fast heart rate. Rarely AVRT can be dangerous.

Symptoms: The most common symptoms are palpitations, dizziness, and shortness of breath, that come and go. More severe symptoms including chest pain and syncope (fainting) are less common. In rare instances, AVRT can be life-threatening.

Treatment: In the acute setting (while the heart is fast), many people find that they can break the tachycardia using vagal maneuvers (bearing down, passive leg raises, etc.). If AVRT continues, it will require an emergency room visit for treatment. Long term, AVRT can be managed with medications or cardiac ablation.

Atrial Flutter and Fibrillation

These rhythms have been placed in a separate category as the management for them is so much different. These can be fast or slow heartbeats, that are regular or irregular.

Atrial Flutter

Explanation: There are several categories of atrial flutter, for simplicity, we will focus on typical atrial flutter. This rhythm is driven by an electrical loop that forms in the upper chamber of the heart. This loop drives the upper chamber of the heart at approximately 300 bpm. This is usually conducted to the bottom chambers of the heart at approximately half that rate, 150 bpm. However, the heart rate can be much faster or slower.

Symptoms: Symptoms are often related to heart rate, at the extremes (fast or slow), people are generally more symptomatic. The most common symptoms are palpitations, dizziness, and shortness of breath. Many people have few or no symptoms. More severe symptoms including chest pain and syncope (fainting) are less common. If rapid flutter continues over days to weeks it can cause cardiomyopathy (weak heart). People with flutter are at increased risk of stroke.

Treatment: In people with minimal or no symptoms, flutter can be managed in the outpatient setting with medications or cardiac ablation. In people with a persistently fast heart rate or with more significant symptoms, an emergency room visit will be needed. Flutter can be managed with medications or cardioversion in the emergency room. Flutter can often be very difficult to manage with medications and may require cardiac ablation. We recommend evaluation by a heart rhythm specialist to discuss management options. Additionally, flutter usually requires treatment with a blood-thinning medication to prevent stroke.

Atrial fibrillation (Afib)

Explanation: Atrial fibrillation is the most common heart rhythm problem in the world with millions of cases in the USA. This rhythm is driven by chaotic electrical conduction in the upper chamber of the heart. This electrical storm can be conducted to the lower chamber of the heart at fast or slow rates. It is typically characterized by an irregular heart rhythm. When in afib, the top chambers of the heart are not contracting effectively. These chambers typically contract (squeeze) forcing blood into the lower chambers, priming them, prior to the lower chambers contracting and pumping blood to the lungs and body. The inefficient heart function in atrial fibrillation results in subtle symptoms.

Symptoms: Symptoms are often related to heart rate, at the extremes (fast or slow), people are generally more symptomatic. Atrial fibrillation symptoms are often subtle, with the most common symptoms being fatigue, frequently people do not know they have afib, because they do not have “cardiac” symptoms. Other common symptoms include palpitations, dizziness and shortness of breath. More severe symptoms including chest pain and syncope (fainting) are less common. If rapid afib continues over days to weeks it can cause cardiomyopathy (weak heart). Most people with Afib are at increased risk of stroke.

Treatment: In people with minimal or no symptoms, afib can be managed in the outpatient setting with medications or cardiac ablation. In people with persistently fast heart rates or with more significant symptoms, an emergency room visit may be needed. Afib can be managed with medications or cardioversion in the emergency room. We recommend evaluation by a heart rhythm specialist to discuss management options. Additionally, afib usually requires treatment with a blood-thinning medication to prevent stroke.

Heart block

These are a set of rhythm abnormalities related to slow conduction or block of electrical conduction within the cardiac electrical system.

1st Degree Heart Block

Explanation: 1st degree heart block results from slow conduction through the AV node.

Symptoms: Generally does not result in symptoms.

Treatment: Generally does not require treatment.

2nd Degree heart Block

2nd degree heart block is broken into 2 categories: Mobitz 1 and Mobitz 2. In people with 2:1 conduction (2 atrial beats for each ventricular beat) it can be impossible to distinguish between the 2 types.

Mobitz 1 Heart Block (Weinkebach)

Explanation: Mobitz 1 heart block results from slow conduction through the AV node. It is characterized by progressive lengthening of the conduction from the upper chambers to the lower chambers until a beat is not conducted. Following the non-conducted beat, the cycle is rest and the conduction time returns to baseline before progressively lengthening again.

Symptoms: People with mobitz1 often have no symptoms. Common symptoms include palpitations, fatigue, dizziness, and shortness of breath. More severe symptoms including chest pain and syncope (fainting) are less common.

Treatment: We recommend an evaluation by a medical professional for anyone with Mobitz 1 heart block. Asymptomatic people with Mobitz 1 often do not require treatment. In people with symptoms, options generally include medication adjustments (if possible) or a pacemaker.

Mobitz 2 Heart Block

Explanation: Mobitz 2 heart block results from slow conduction below the AV node. It is characterized by consistent conduction time from the upper chambers to the lower chambers until a beat is not conducted. Typically the conduction time before and after the dropped beat is similar.

Symptoms: People with Mobitz 2 may have no symptoms. Common symptoms include palpitations, fatigue, dizziness, and shortness of breath. More severe symptoms including chest pain and syncope (fainting) can occur.

Treatment: People with Mobitz 2 require an evaluation by a medical professional, preferably a heart rhythm specialist. Mobitz 2 heart block can be dangerous and usually requires a pacemaker.

3rd Degree Heart Block

Explanation: 3rd Degree Heart Block (complete heart block), is a complete failure of the conduction of electricity from the top chambers to the bottom chambers. This means the heart’s normal pacemaker (SA node) is disconnected from the lower chambers, typically resulting in a slow heart rate, which can be very dangerous. The severity of symptoms typically correlates to the heart’s “escape” rate. This is the heart rate of the lower chambers during 3rd degree heart block, which can vary widely from person to person.

Symptoms: People with complete heart block often have severe symptoms, including syncope (fainting), fatigue, dizziness, chest pain. 3rd degree heart block can be fatal. Rarely people are minimally symptomatic or asymptomatic.

Treatment: People with complete heart block, need immediate evaluation by a medical professional. This rhythm is considered dangerous and can be fatal.

Non-Specific Pause

Explanation: On some single lead ECGs the atrial activity can be very difficult to see, but usually ventricular activity is clear. If the interpreting doctor is unable to clearly discern atrial activity, then it is impossible to further characterize a pause. In this case, a pause may represent sinus arrhythmia, a PAC that does not conduct to the ventricle, or 2nd or 3rd degree heart block.

Treatment: As we are not able to completely classify these types of pauses, we recommend further evaluation by a medical professional.

Intervals

P wave: The p wave represents the contraction of the upper chambers of the heart, the right and left atrium.

PR interval: The PR interval represents the time from the start of atrial (upper chambers) contraction to the beginning of ventricular (lower chambers) contraction.

  • Long PR interval represents the delay in the conduction from the atrium to the ventricle
    • This finding is discussed in more detail in the heart block section
  • Short PR interval represents a short time between atrial and ventricular contractions, as the name suggests, we recommend people with a short PR interval be evaluated by a medical professional
    • This can represent ventricular pre-excitation, a junctional heart rhythm, or more rare syndromes

Delta Wave: This represents preexcitation of the ventricle, commonly referred to as Wolf-Parkinson-White (WPW) Syndrome. This can lead to AVRT as discussed in the supraventricular tachycardia section.

QRS Duration: this represents the contraction of the lower chambers of the heart, the left and right ventricles.

  • Intraventricular conduction delay: this is caused by a delay in the conduction into the ventricles (lower chambers), the most common cause of delay is a bundle branch block. There are 3 bundles that typically connect the upper and lower chambers of the heart. The left bundle branch is made up of the left anterior fascicle (LAF) and left posterior fascicle (LPF), making up 2 of the bundles. The third is the right bundle branch. It can be very difficult to tell the cause of intraventricular conduction delay on a single lead ECG.
    • Left bundle branch block: this occurs when there is block or significant delay of conduction through the left bundle.
    • Right bundle branch block: this occurs when there is conduction block or significant conduction delay in the right bundle

ST Segment, T Wave: The ST segment represents the time between electrical depolarization of the ventricle and repolarization, the time the ventricle is squeezing before relaxing. The T wave represents repolarization or relaxing of the ventricle.

  • Non-specific ST changes: Elevation and depression of this segment or inversion of the T wave can have important implications. Unfortunately, these changes are impossible to interpret on a single lead ECG, that is why we refer to them as non-specific changes. We recommend people with these changes be evaluated by a medical professional.

QT Interval and QTc: This represents the time from the beginning to the ventricular contraction to near the end of relaxation. The QTc is the QT interval mathematically corrected for heart rate.

  • Prolonged QT or QTc Interval: this can be difficult to measure on a single lead ECG, and may be over or underestimated. QT can be lengthened due to genetic abnormalities, electrolyte imbalances, and a long list of medications. We recommend all people with a prolonged QT have further evaluation by a medical professional for a more accurate assessment.

U Wave: These are thought to represent delays in repolarization (relaxing) of the ventricle.

  • Prominent U wave can be seen in the setting of electrolyte abnormalities, or occasionally in people genetic abnormalities affecting the heart
  • Inverted U waves are more concerning and can be seen in the setting of myocardial ischemia (heart attacks), coronary disease, and structural heart disease.
  • We recommend all people with a U wave identified have further evaluation by a medical professional for a more accurate assessment.

Still have questions?

Phone: (214) 206-4099
Email: support@myecgmd.com
Mon-Fri 8am-8pm ET (12pm – 12am GMT)
Sat & Sun 10am-7pm ET (2pm – 11pm GMT)
Address: Texas Cardiac Rhythm Specialists, PLLC, 208 Hewitt Dr. Ste 103-211, Waco, TX 76712