Angina ECG vs. Normal ECG

Many of us, scientists and lay population alike, would argue that the heart is the most crucial part of the body. Indeed, cardiovascular problems constitute a great cost to society, both financially and from a health perspective because of the large number of affected patients. Angina Pectoris is one of the most common heart conditions. However, a large body of research allows us to understand and detect this disorder. 

This article outlines the definition of angina, its causes, symptoms and treatment, as well as information about the electrocardiogram test (ECG) and how it is interpreted to detect heart problems. 

What is Angina?

Angina refers to a tight pain in the chest caused by a disruption in blood flow along coronary arteries – the vessels that supply oxygen and nutrients, which are crucial for the heart to function. Said arteries become narrowed, reducing the amount of blood that can flow through them and therefore the amount of oxygen the heart receives. Why the vessels narrow will be discussed further below. As the heart is responsible for pumping blood around the body, inadequate oxygen supply constitutes a problem, especially at high levels of activity when its need increases. 

Although angina is not a disease by itself, it can be a symptom of coronary artery disease (CAD), a more serious condition which can lead to myocardial infarction (heart attack). Therefore, even though angina alone isn’t life-threatening, can be a warning sign of more serious heart problems and requires medical attention. 

Types of Angina

There are four types of angina depending on its specific cause.

• Stable angina: It’s the most common type of angina. It’s triggered by situations in which our heart needs more oxygen, such as physical exercise or stress, and goes away with rest or medication. Stable angina usually lasts a few minutes.
•  Unstable angina: As opposed to stable angina, unstable angina can start in the absence of exercise or stress, tends to last longer and doesn’t go away with rest or medication. It’s a more serious condition that requires urgent medical help.
•  Variant angina: Also referred to as Prinzmetal’s angina, variant angina is an uncommon type. It’s caused by vasospasm (a sudden narrowing of the artery) and happens at rest, sometimes during sleep.¹
• Microvascular angina: Like variant angina, its cause is vasospasm, but in this case, the vessels affected are thin coronary arteries (hence the term microvascular). Microvascular angina is triggered by exercise or anxiety.

Signs and Symptoms

The main symptom of angina is tight chest pain, a feeling as if a strong force was pressing on the thorax. The pain may spread to the arms, shoulders, neck or jaw. Other symptoms include shortness of breath, fatigue, nausea, dizziness and sweating.² In addition, experiencing angina often produces anxiety and nervousness. Symptoms usually last a maximum of 10 minutes; if the pain stays for longer, it could indicate a more serious heart condition such as a heart attack, and emergency care should be sought.

Causes and Risk Factors

Angina is caused by an insufficient blood supply to the heart, which leads to too little oxygen available for the heart to function properly, eventually triggering a pain sensation. The medical term for a lack of oxygen in the cardiac muscle is ischemia.

The cause of insufficient blood supply in angina is a narrowing of the coronary arteries that supply blood to the heart tissue. This narrowing is usually a result of atherosclerosis: the build-up of fat on the walls of the arteries, making the space through which blood can flow smaller.² Sometimes, angina can also be caused by vasospasm (a sudden narrowing of the artery), leading to, again, reduced blood flow.³ 

Risk factors of angina include:

Figure: Risk Factors for Angina

Created by Aastha Malik

Diagnosis

The first step for an angina diagnosis usually involves visiting a GP and describing the symptoms. This will allow the doctor to rule out any other potential causes of chest pain, such as a panic attack or rib injury. After this, there are several tests that can be carried out to diagnose angina and assess cardiovascular health.

Electrocardiogram (ECG)

An ECG is usually the first test carried out to check for abnormal heart activity. How it works and how its results are interpreted will be described in detail later in the article.

Stress test

In this case, stress refers to a situation in which the heart is required to work harder. A stress test involves monitoring heart activity and rhythm, usually by an ECG device, while the patient walks or jogs on a treadmill.

Coronary angiogram

This is a useful x-ray that provides images of the coronary arteries and how well they supply blood to the heart. It’s a more invasive test that involves inserting a catheter (a small tube) through the groin, and moving it up to the heart. A coronary angiogram can detect abnormally narrow vessels

Blood tests

High levels of the protein troponin can indicate heart muscle damage. Blood tests can also measure cholesterol levels, a risk factor for atherosclerosis

Treatment

Specific treatment varies depending on the type of angina as well as its severity. It ranges from medication to, in the most serious cases, surgery.

Medication

• Nitrates: commonly used for quick pain relief. They work by widening the arteries (vasodilation).
• Beta-blockers: a common medication for heart conditions. They reduce the need for oxygen by decreasing blood pressure and heart rate.
• Calcium-channel blockers: there are several different types of calcium-channel blockers, but they all act by increasing vasodilation. Some also lower heart rate and blood pressure as well as prevent vasospasm.
• Ranolazine: a drug that also reduces oxygen demand; however, it does not lower heart rate or blood pressure.
• Aspirin: This common painkiller also helps prevent blood clots, which constitute a major risk factor for heart attack as they block the vessels.

Surgery

• Coronary angioplasty: a small tube with a balloon tip is inserted and moved up towards the chest into the blocked coronary artery. The balloon tip inflates, opening up the vessel to increase blood flow. The balloon is later deflated, and the catheter removed. On some occasions, a wire mesh called a stent is kept on the walls of the artery to prevent it from being blocked again. 
• Coronary bypass: blood flow along a blocked coronary artery is redirected by inserting a small piece of a blood vessel from a different part of the body, often the leg.

Prevention

Although not much can be done about some of the factors that increase the risk of angina, such as a family history of heart disease, following a healthy lifestyle and taking care of overall health can help prevent this cardiovascular disease. Listed below are some possible lifestyle changes you can make to reduce your risk of developing angina:

• Follow a balanced diet, low in cholesterol and saturated fats
• Maintain a healthy weight
• Stop smoking
• Reduce alcohol consumption
• Reduce sources of anxiety and stress, and seek psychological help if applicable 
• Increase cardiovascular exercise, such as walking or jogging regularly
• Correctly manage diabetes 
• Correctly manage high blood pressure

Complications

Myocardial infarction (heart attack)

Suffering from angina significantly increases the risk of myocardial infarction (heart attack).³ The difference between angina and a heart attack is whether any heart muscle cells die as a result; in angina, there is no loss of tissue. However, during a heart attack, the lack of blood flow is so severe that some regions of the heart may be left dysfunctional due to a prolonged lack of oxygen.⁵ Therefore, a heart attack may have long-lasting consequences and require more serious surgical interventions and further treatment.

Surgery risks

Angina can sometimes require surgical intervention, which comes with its risks, such as excessive bleeding or the formation of blood clots.

Life quality

The symptoms of angina can also impact the quality of life, as daily activities may need to be adapted to reduce the risk of more cardiovascular damage.

What is an ECG?

An electrocardiogram (ECG or EKG) is a common, short cardiovascular test that records the heart’s rhythm and electrical activity. 

What Does an ECG Measure?

Every heartbeat carries and is triggered by electrical activity; an ECG detects electrical impulses at different points in the heart, recording their strength, rhythm and regularity. 

In an ECG trace, each waveform represents a heartbeat. The results of the test will show several lines of this waveform pattern repeating itself. The shape and regularity of the waves observed can help determine any abnormalities in heart function. 

How is an ECG performed?

An ECG can be carried out at a hospital or a doctor’s clinic. The patient is asked to lay on their back and remove any upper clothing, leaving the chest bare. A doctor then places small patches on the thorax; sometimes, they will also be placed on the arms or legs. These patches are called electrodes and are connected to a computer through wires. The electrodes will pick up and record heart activity, which is transferred to the computer and show up on the screen as waves. A video demonstration by the NHS can be found here.

Who Performs an ECG?

An ECG is ordered by a cardiologist or a GP, and is usually performed by a medical technician.

Exercise ECG

An exercise ECG is performed while the patient exercises, usually walking or jogging on a treadmill. Heart activity is recorded to find out how well the muscle works under stress conditions when abnormalities are more likely to show up in an ECG test.

Static ECG

In contrast to an exercise ECG, a static ECG is carried out when the patient is at rest, with lower heart activity.

ECG Waveform Segments and Their Meaning

The general ECG has 5 identifiable waves: P, Q, R, S and T. On some occasions, an additional wave, called U, can be observed. The characteristics of each wave and the segments between them can provide doctors with detailed information about electrical activity in different parts of the heart, and as a result, help identify abnormalities.

The P wave is a slight upwards wave at the start of each heartbeat waveform. It represents the electrical activation of the atria (the two small upper chambers inside the heart), which precedes their contraction.

The PR segment is the flat line between the end of the P wave and the onset of the QRS complex. Its elevation is used as a baseline measure for the ECG.

The QRS complex usually includes a short downwards wave (Q), a sharp upwards wave (R) and a further negative wave (S). It represents the activation of the ventricles (the two lower, larger chambers inside the heart) just before they contract.

The ST segment starts at the J point, which occurs just after the QRS complex. This part of the ECG wave is of special importance when diagnosing angina or a heart attack.

The T wave is a smooth upwards wave that constitutes the end of the ST segment. It represents ventricle relaxation.

Sometimes, an additional small upwards wave can be observed after the T wave. This is called the U wave.

The QT interval is the time between the onset of the QRS complex and the end of the T wave, which represents the time between ventricle contraction and relaxation. Its duration holds an inverse relationship with heart rate: the larger the QT interval, the slower the heart rate, and vice versa. Because of this, the QT interval value is usually converted through a mathematical formula to the QTc (corrected QT)⁶. This allows doctors to assess ventricular function without the influence of heart rate.

How is the ECG Result Changed in Angina Patients?

Heart Attack and ECG

Myocardial infarction or heart attack is a serious cardiovascular event characterised by the death of cells within the heart due to a prolonged lack of blood flow.⁷ Myocardial infarction and angina have the same cause - insufficient blood flow to the heart. The physiological difference is that the former results in cell death, whereas the latter doesn’t. 

An ECG can detect myocardial infarction. The ECG trace of an affected patient will show certain characteristics and wave abnormalities including ST-segment elevation or depression, T wave irregularities and (abnormal) QT intervals.

What is ST-Segment Elevation and Depression?

ST elevation is defined as an abnormally high ST segment. It’s one of the main signs of a serious type of heart attack called a STEMI (ST elevation myocardial infarction).⁸

ST segment depression is also sometimes observed in heart attack and unstable angina patients.⁹ Heart attacks that don’t present ST elevation on an ECG are called NSTEMI (non-ST elevation myocardial infarction). They are usually less severe than STEMIs.

Negative vs. Positive T-Wave

A negative T wave alone is usually not a cause of concern. However, when observed in addition to an abnormal ST segment, an inverse T wave can indicate acute myocardial ischemia.⁹ The term acute means that the lack of oxygen in the heart is ongoing when the ECG is recorded. 

A positive T wave is expected in healthy individuals. However, an abnormally high T wave, called hyperacute, is sometimes found in variant angina and can also be an early sign of STEMI. It can also indicate disease in the case of T wave pseudonormalisation.

T-wave pseudonormalisation

Sometimes, patients who had shown negative T waves in past healthy ECGs may display positive T waves when presenting with symptoms of angina.¹⁰ So, although the reversing of the wave from negative (uncommon) to positive (seen in healthy individuals) could seem to indicate better cardiovascular activity, it’s actually a symptom of the disease.

Negative U-Wave

A negative U wave may also indicate abnormal heart activity. It’s regarded as an early sign of different types of angina or myocardial infarction.

Prolonged QTc interval

A slightly longer QTc interval than usual can be a symptom of myocardial ischemia, and it can also help predict future events related to coronary artery disease.¹¹

However, this is not the same as long QT syndrome, a condition in which the interval duration is much more extended than standard due to electrical activity abnormalities in the heart. 

Summary

Angina refers to tight chest pain due to insufficient flow of oxygen to the heart as a result of reduced blood flow. The specific cause for this is a narrowed coronary artery, although the nature of this narrowing depends on the type of angina. While it’s not a severe disease itself, angina can lead to serious future conditions, such as a heart attack.

One of the most common tools for diagnosing angina is an ECG, a test which measures electrical activity within the heart. The shape and duration of its waves and segments can help detect abnormalities in the patient, which in turn leads to a quick medical response to start treating the condition. Treatment for angina includes various forms of medication, lifestyle changes and, in the gravest cases, coronary artery surgery.