ECG abnormalities finding, causes, & examples

ECG abnormalities Posted On


In my last post, I explained the basic interpretation of an ECG report. Now, we will discuss how to read ECG abnormalities in different heart pathological conditions. 

If you want to know whether your heart is working correctly or not. In that case, ECG is the best and easiest technology to detect many heart problems like heart attack, arrhythmias, ischemic heart disease, etc. 

Here, you are going to learn the abnormalities of ECG waves with various examples.   

ECG gives information about the history of heart disease and also forecasting future heart disease.  

Let’s see the various examples and causes of ECG abnormalities –


Heart rate abnormalities 

Naturally, the heart is under-influenced by the autonomic nervous system, i.e., parasympathetic and sympathetic outflow. This outflow helps to control the automaticity of the heart. 

Usually, every component of your heart has its own heart rate. It starts the electrical activity from the SA node (60 to 100 bpm), then conduction goes to the AV node (50 bpm). After that, it diverted into the left bundle branch and right bundle branch (30 to 40 bpm) by Purkinje fibers

ECG abnormalitiesSuppose your SA node is unable to provide electrical activity due to any pathological conditions. In that condition, other components of your heart will start to beats at their own rate. 

Heart rate (pulse rate) represents the number of beats of your heart in a minute. In other words, how many times your heart pushes the blood to the rest of your body. The normal heart rate is 60 to 100 bpm. 

It is straightforward to calculate heart rate. You need to just count large squares in between R-R interval and then divide it by 300. 

If you got 5 large squares in between R-R interval = 300/5= 60 bpm

Similarly, if there is 4 large square = 75 bpm

3 large square = 100 bpm

2 large square = 150 bpm

1 large square = 300 bpm


If you get fewer large squares in between R-R intervals, that represent a fast heart rate. This rapid heart rate is called sinus tachycardia (more than 100 bpm). It means the SA node is firing more frequently. It mainly occurs when you have a fever, pain, anxiety, stress, hyperthyroidism problem, and during exercise.

If the large squares are more in between R-R intervals representing slow heart rate, called sinus bradycardia (under 60 bpm). It generally happens in the condition of hypothyroidism, hypoglycemia, liver problems (like jaundice), hypothermia, and during sleep conditions. 


Tachy-Brady Syndrome (Sinus Tachycardia + Sinus Bradycardia)

If you observe fast heart rate (sinus tachycardia) initially and then slow heart rate (sinus bradycardia) later in the ECG graph. This type of arrhythmia is called Tachy-Brady Syndrome. It is also known as Sick Sinus Syndrome

In this condition, your heart sometimes beats too quickly and sometimes beats too slowly. 

Naturally, the electrical activity of your heart originates from the SA node. Due to this, you may see an upright P wave + narrow QRS complex. 

But suppose your heart’s electrical activity originates from the AV node. In that case, ECG reflects P wave absent + narrow QRS complex.


  • If electrical activity starts from atria = P wave absent + narrow QRS complex + R-R distance very close
  • If electrical activity starts from ventricles = P wave absent + wide QRS complex.


ECG abnormalities in heart rhythm

After calculating the heart rate, you need to check heart rhythm. It represents the pattern of heartbeats.

The disturbances in heart rhythm cause arrhythmia. Here, you need to check R-R distance is the same or not.

If the R-R distance is the same or equal, then it is a regular rhythm.

If the R-R distance is unequal, then it will be an irregular rhythm.


Abnormal P wave in ECG

In ECG, the P wave represents atrial depolarization. P wave abnormalities indicate a problem in the upper chamber (atrium) of your heart. 

It may be a type of – 

a. Multiple P-wave forms 

If you find more than one P wave in the ECG pattern followed by a QRS complex, it is called Atrial Tachycardia. 

In these multiple atrial activities, your heart generally beats fast, around 125-250 bpm. It is not much life-threatening, but it may be a sign of severe heart problems and breathing problems. 

Your doctor may clinically coordinate the ECG results with your symptoms. 


b. Appearance of F wave 

If your heart beats too fast in the upper (atrium) chamber, it will form a tooth-like shape (sawtooth). 

Here, you will see inverted P waves followed by a QRS complex with irregular heart rhythm. This type of wave is known as the F wave. Sometimes, it is difficult to recognize. It is usually seen in Atrial Flutter arrhythmia (250-350 bpm). It may be due to heart muscle damage. 

Due to this type of ECG abnormalities, you may experience palpitation, shortness of breath, fatigue, and fainting. 

ECG abnormalities


c. Absence of p waves   

If you don’t find any P – wave in ECG paper, it represents Atrial fibrillation.

It means there is chaotic electrical activity in the upper chamber with a rapid heart rate, around 350-550 bpm. 

It indicates your heart is not circulating enough blood to your body. Due to this, it may lead to heart failure, pulmonary embolism, COPD (Chronic Obstructive Pulmonary Disease), ischemic heart disease, acute Myocardial infarction, and atrial septal defects.

ECG abnormalities

In these ECG abnormalities, you will see no P wave or a very small fluctuation in baseline followed by a QRS complex with irregular heart rhythm. 

Long-standing hypotension is also a cause of Atrial fibrillation because it reduces the filling time (diastolic interval). It means your heart is unable to fill ventricles appropriately because of rapid heart rate. 

Under this circumstance, it causes decreased cardiac output and reduces blood pressure. 

Note – If you find an increased P wave in height and length, it indicates enlargement of the heart’s upper chamber (atrium).  


Abnormal PR interval in ECG

PR interval (P wave + PR segment) represents electrical activity from the SA node to the AV node. AV node act as a gatekeeper which holds the current for 0.1 sec. 

Here, the AV node is your primary culprit. The ECG abnormalities in PR intervals represent junctional or nodal arrhythmia.  

a. Delta wave with no PR segment

If you find a quick or disappear PR segment followed by a wide QRS complex. It forms a deep sleep wave or delta wave. This type of abnormality in ECG is called Junctional tachycardia.

It is also called WPWS (Wolff-Parkinson-White Syndrome). 

ECG abnormalities

In this syndrome, an extra conduction pathway (bundle of Kent) is formed. This pathway directly connects from the atria to the ventricles and bypasses the AV node.

It may be in two forms – 

Type A pre-excitation = If electric pathway communicates between the left atrium and the left ventricle.

Type B pre-excitation = If electric pathway communicates between the right atrium and the right ventricle

Due to this, you may feel a fast heartbeat, shortness of breath, palpitation, lightheadedness, and fainting.

The cause of WPWS is unknown. But it is most commonly seen in congenital heart disease patients.

This type of ECG abnormalities may worsen your condition if you have too much coffee, do an excessive workout, too much alcohol consumption, and an anxious state. 


b. Long PR interval 

Long PR interval represents abnormalities from the beginning of the P wave and until the starting of the QRS complex. It gives ideas about the degree of heart block

It is also called Junctional bradyarrhythmia, junctional blocks, nodal blocks, or heart blocks. 

First-degree heart block – It usually happens during pathological prolongation of the PR segment. In this condition, every P wave followed the QRS complex but an unusual delay of the PR segment. So, you may see a prolongation of PR interval (greater than 0.2 sec.)


Second-degree heart block – All P waves are not followed the QRS complex. There are two types of second-degree heart block.

Mobitz 1 (Wenckebach) – Prolonging PR interval

You will observe gradual prolongation of every PR segment until one P wave fails to conduct to the ventricles. 

It occurs due to blockage of AV junction conduction. 

ECG abnormalities


Mobitz 2 – The PR segment will remain the same and stable. But sometimes, you will occasionally miss (P wave+PR segment+QRS complex). 

It may be in 2:1 (two P waves after each QRS complex)

ECG abnormalities


Third-degree heart block – In this block, there is AV dissociation, which is called complete heart block. It means electrical activity can’t pass through the atria to ventricles. 

Due to this, ventricles need to conduct electricity at their own rate (30-40 bpm). So, the P wave and QRS complex won’t be stable here. 

In this circumstance, you should avoid drugs like calcium channel blockers (amlodipine, verapamil, nifedipine, etc.), digitalis, beta-blockers (propranolol, atenolol, metoprolol, etc.), and adenosine. These drugs slow down the AV node.  


Abnormal R wave progression

To examine the R wave progression, you need to carefully look at precordial chest leads.

In a normal ECG report, you will see a small R wave and a deep S wave in the V1 lead.

You need to focus only on R wave deflection. As you move from V1 to V5, you will find R wave is progressively increasing or taller. This is called R wave progression. 

But in V6, the R wave is less tall than V5 because it is applied in the mid-axillary region. 

In case if you find an abnormal increase in the size of the R wave is called poor R wave progression. It indicates acute myocardial infarction, left ventricular hypertrophy, and right ventricular hypertrophy. 


Abnormal QRS complex 

a. Axis deviations

Axis deviation gives information about the direction of the heart. If your left heart muscle is week and your right heart muscle is strong, then it moves towards the left.

To check the axis deviation, you need to observe the QRS complex in Lead I and aVF.

Normally, QRS shows positive deflection in both – Lead I and aVF. 

Suppose you find positive QRS deflection in the Lead I and negative QRS deflection in aVF; it represents LAD (Left Axis Deviation). It is most commonly seen in left ventricular hypertrophy.

On another side, you find negative QRS deflection in the Lead I and positive QRS deflection in aVF; it represents RAD (Right Axis Deviation). It is often seen in right ventricular hypertrophy.


b. Bundle branch block in ECG

It does not indicate the problem in the blockage of arteries. 

It represents the only failure of electrical activity in the ventricles. The blockage may be seen either in the right bundle branch or the left bundle branch. 

The normal width of QRS is 0.06 to 0.10 sec. If the width is more than 0.12 sec, then there is a bundle branch block. 

To determine the location of blocks, you need to check V1 lead represents the right side of the heart and the V6 lead represents the left side of the heart. 

Right bundle branch block (RBBB) – It refers right ventricular hypertrophy. RBBB is not much serious concern, but it gives a signal for conditions like anterior wall MI, cardiomyopathy, and pulmonary embolism. 

You may find the “rSR” wave. R – Prime represents terminal R. It means two R waves reflect in lead V1 – a small wave – “r” and a large wave – “R” with a wide QRS complex.  

In lead V6, slurred S wave may be present. 


Left bundle branch block (LBBB) – It represents left ventricular hypertrophy. It rarely happens but is life-threatening. It is caused by hypertensive heart disease, aortic stenosis, and ischemic heart disease

You will see these characteristics in ECG if there is LBBB – 

  • Wide QRS complex
  • No Q waves in lead V6
  • Tall notch R wave (M – shape) in lead V6
  • Deep S wave in lead V1
  • T wave negative deflection


Abnormal ST segment in ECG

ST segments represent the plateau phase interval between depolarisation and repolarisation. If there is any disturbance in shape, height, and duration of ST segments show abnormalities – 

a. ST-elevation 

If you find uprighted and elevated ST-segment above the baseline, it represents ST elevation. 

It is also called STEMI (ST-elevation myocardial Ischemia). It also represents early repolarization. 

ECG abnormalities

This type of ST-elevation indicates –

  • Myocardial ischemia 
  • Transmural ischemia (ischemia in an entire thick wall – endocardium, myocardium, and epicardium)
  • Hyperkalemia (high potassium level near the ischemic region) 
  • Other associated heart defects. 


The infarction may occur in any part of your heart. To find the ST elevation, you need to check – 

  • Lead II, Lead III, and aVF refer to an inferior (below) portion of the heart
  • Lead I, aVL, V5, and V6 refer to the lateral (towards the right side) part of the heart
  • V1 and V2 refer to the anteroseptal (front of the septum) portion of the heart.
  • V3 and V4 refer to the anteroapical (front of bottom) part of the heart.


b. ST-segment depression 

If you find ST-segment below the standard baseline in ECG, it is called ST-segment depression.

It forms a J curve. It may be determined by V5, V6, aVF, and Lead III.

ST-segment depression is mostly seen in patients with hypokalemia, 

subendocardial ischemia, medications such as digitalis, and other heart problems. 

ECG abnormalities


Prolong the QT interval

In a healthy person, the QT interval covers 10 small squares with 0.4 secs. If it is longer than normal represents long QT syndrome.

Long QT interval responsible for torsades de pointes. It is a special form of polymorphic ventricular tachycardia that twisting around the baseline. 

There are few characteristics of Torsades de points, which reflects in ECG lead II or V5, V6 – 

  • High heart rate = 150-250 bpm
  • Rhythm = irregular
  • P wave = absent
  • QRS complex = wide QRS complex with changing amplitude.


It is such a life-threatening condition. You may have experienced rapid heartbeat, fainting, seizure, and sudden deaths. 

The main cause of QT prolongation maybe – 

  1. Genetic reason – congenital long QT syndrome.
  2. Drug-induced QT prolongation – amiodarone, quinidine, ibutilide, erythromycin, ciprofloxacin, citalopram, escitalopram, haloperidol, and sotalol. 
  3. Electrolyte imbalances – hypokalaemia, hypomagnesemia, and hypocalcemia.



Now, you have got a complete idea of how ECG technology is beneficial for us. It provides a lot of information about heart diseases by ECG abnormalities.

Your doctor uses this tool to diagnose your disease. But it needs to correlate with your symptoms. 

If you found this post (ECG abnormalities) informative, please share it on social media to spread knowledge. 


Source – Lippincott Williams and Wilkins. ECG interpretation. Made incredibly easy. Wolters Kluwer Health, 5th edition, 2011.


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