Posterior Myocardial Infarction (Heart Attack)

What is Posterior Myocardial Infarction (Heart Attack)?

A heart attack, or myocardial infarction (MI), often leads to chest pain and can cause serious health problems and even death. A specific type of heart attack, called a posterior wall myocardial infarction, happens when the blood flow to the back part of the heart gets blocked. This condition often happens alongside other types of heart attacks, but when it happens alone, it’s hard to diagnose. This is because the changes seen on an EKG, which is a test that monitors heart activity, are less noticeable. As a result, this condition is often overlooked or mistaken for something else. Quick identification of this type of heart attack is essential, as it allows for proper treatment and a lower risk of complications, including death.

What Causes Posterior Myocardial Infarction (Heart Attack)?

A heart attack, or myocardial infarction, is typically caused by a reduction in the blood flow to the heart. This is often due to the rupture of an atherosclerotic plaque or a clot inside the blood vessel, known as Type I myocardial infarction. However, a heart attack can also occur when the heart muscle is deprived of oxygen either due to increased demand or limited supply, referred to as a Type II myocardial infarction. Conditions like high or low blood pressure, spasms in the coronary artery, anemia, infection in the bloodstream and abnormal heart rhythms can trigger this type of heart attack.

A posterior myocardial infarction happens when the blood flow to the back of the heart is disrupted. The heart’s blood supply is primarily provided by two main arteries: the right coronary artery and the left main coronary artery. The latter, a short and wide vessel, splits into the left anterior descending (LAD) artery and the left circumflex artery (LCx). Sometimes, a small branch named the ramus intermedius emerges between these two arteries. In about 70% of people, the right coronary artery delivers blood to the posterior descending artery which supplies the back of the heart – this is known as “right dominant” circulation. In about 10% of people, this job is done by the LCx artery, referred to as “left dominant” circulation. The remaining 20% of the population has both these arteries supplying the posterior descending artery, called co-dominant circulation. A blockage in these arteries leads to a lack of oxygen in the area they supply. The patient’s anatomy dictates which arteries provide blood to the back of the heart.

There are several risk factors for developing coronary artery disease and heart attacks. For individuals aged over 21 years presenting with symptoms that suggest acute coronary syndrome (ACS), the HEART score is used. This tool helps determine the risk of experiencing a significant heart-related event within the next six weeks. It does not apply in certain situations like if there are new changes in heart’s electrical activity seen on an EKG, low blood pressure, or other severe health conditions. However, the risk factors remain important for anyone suspected of having ACS. They include high blood pressure, high cholesterol levels, diabetes, obesity (Body Mass Index over 30), current smoker or quit within three months, history of heart disease in the family (a parent or sibling diagnosed before age 65), and history of atherosclerotic disease, which could include previous heart attacks, angioplasty, bypass surgery, stroke or mini-stroke, or peripheral artery disease.

Risk Factors and Frequency for Posterior Myocardial Infarction (Heart Attack)

A posterior myocardial infarction, which refers to a type of heart attack that affects the back wall of the heart, represents 15% to 21% of all heart attacks. It is frequently linked with heart attacks that occur in the bottom or side walls of the heart, leading to a significant area of damage. Isolated posterior heart attacks, detected using specific testing leads, occur about 3.3% of the time. This figure might be an underestimate because these types of testing leads are not routinely used.

In addition, certain factors are associated with a late appearance of Acute Coronary Syndrome (ACS), a term that covers a range of conditions caused by a sudden, decreased blood flow to the heart. This includes being female, of older age, Black or Hispanic, having low educational status, and being of low socioeconomic status.

• Women are less likely to receive treatment based on medical guidelines and are less likely to undergo heart catheterization.
• While men usually report central chest pain, women might experience less typical symptoms.
• These atypical symptoms can include fatigue, shortness of breath, indigestion, nausea or vomiting, heart palpitations, or weakness.

Signs and Symptoms of Posterior Myocardial Infarction (Heart Attack)

Chest pain is a common reason people rush to the emergency department. It’s crucial for doctors to think about a wide range of potential causes. There are six particularly serious issues that doctors need to rule out quickly because they can be life-threatening. These are heart attacks, severe heart inflammation, a tear in the main artery of the body (the aorta), a blood clot in the lungs, a punctured lung, and a tear in the esophagus (the tube that connects your throat to your stomach).

In emergencies, patients reporting chest pain are usually given an EKG (a test that checks how your heart is working) immediately. However, the EKG results alone are not enough to make a diagnosis. Doctors need to compare the new EKG with previous ones and consider other potential causes to avoid missing something critical.

Doctors will ask about your symptoms – when they began, how long they last, what makes them worse or better, what they feel like, and if there are other symptoms. For example, heart attacks often come with a crushing pressure in the chest, a feeling some patients describe as “an elephant sitting on my chest.” This pressure can sometimes spread to the arms, jaw, or upper abdomen. Heart attack patients might also feel nauseous, sweat excessively, or feel worse when they’re physically active or emotionally stressed. On the other hand, pain that feels sharp or stabbing, lasts for less than a minute, changes depending on your body position, or can be reproduced by applying manual pressure, is less likely to be due to a heart attack.

However, grave heart conditions cannot be ruled out based on these factors alone. In such cases, doctors will look for additional signs of conditions that could potentially cause chest pain, such as blood clots in the lungs. These signs could include a recent history of swelling in one leg, surgery or trauma, hormone use, or being immobilized for extended periods. Similarly, chest pain following a physical strain or injury might signal a muscle problem. Conditions such as acid reflux, gallstones, and ulcers could also cause chest pain.

You can expect doctors to perform a physical exam for everyone complaining of chest pain. This includes monitoring your heart rate and blood pressure, examining your general appearance, inspecting your neck and chest, and listening to your heart and lungs. Notably, a substantial difference in blood pressure between your arms could indicate a tear in your aorta. They will also examine your abdomen, arms and legs, and evaluate your nerve function.

• Factors that increase the probability of a heart attack:
  • Nausea or vomiting
  • Excessive sweating
  • Pain gets worse with physical activity or stress
  • Chest pain spreading to the arms or jaw
• Factors that decrease the probability of a heart attack include:
  • Sharp or stabbing chest pain under one minute
  • Pain that changes with body position
  • Pain that can be reproduced by pressing on the chest

If your heart stops beating (cardiac arrest) and you need to be revived, and the cause of the arrest was an irregular heart rhythm, doctors recommend that you undergo a heart procedure to visualize and treat potential blockages in the heart arteries (coronary angiography) once you’re stable.

Testing for Posterior Myocardial Infarction (Heart Attack)

If a patient comes in with chest pain that suggests they might have acute coronary syndrome (ACS), several tests should be conducted. These include a detailed medical history and physical examination, an electrocardiogram (EKG), and assessment of specific cardiac proteins in the blood known as cardiac biomarkers.

The EKG, also known as an ECG, is a crucial test that measures the electrical activity of the heart. It uses 12 leads or sensors placed on the patient’s body: four on the extremities and six on the chest. These sensors read the heart’s electrical signals, helping doctors identify which area of the heart might be damaged.

In a typical 12-lead EKG, some heart damages might be hard to detect due to the lead placement. For example, the EKG might not show visible changes for a heart attack occurring in the back of the heart (posterior myocardial infarction). In these cases, additional leads (V7-V9) can be attached to the patient’s back for a better assessment.

While the displacement of these additional leads can give more subtle results, an elevation greater than 0.5 mm in one of these leads shows a possible posterior heart attack. Other changes, such as ST-depression in the anterior leads or larger than usual R-waves in V2-V3, can also be indicative of a potential heart attack at the back of the heart. Doctors will often compare the current EKG to older ones to observe any changes.

Afterward, the patient might need to take some blood tests, including complete blood count (CBC), metabolic profile, troponin, coagulation studies, and possibly B-type natriuretic peptide (BNP). These tests can provide additional information about the heart’s condition and potential heart damage.

Apart from EKG and blood tests, imaging tests might be required. A chest X-ray can be taken right at the patient’s bedside, and a bedside echocardiography might also be considered. Echocardiography is an ultrasound test that gives images of the heart, providing valuable information about heart size, blood flow, and heart muscle health. Although it requires a trained operator, it can help in the diagnosis of ACS.

Treatment Options for Posterior Myocardial Infarction (Heart Attack)

The best way to treat acute posterior STEMI, a type of heart attack, is with therapy to restore blood flow, or reperfusion therapy. Ideally, this is done through a procedure called percutaneous coronary intervention (PCI). However, if PCI is not available or can’t be started within 120 minutes, then fibrinolytic therapy, which uses medication to dissolve blood clots, should be given within 30 minutes.

There are several additional treatments that can support reperfusion therapy:

• Aspirin: If STEMI is suspected, aspirin should be given immediately. It can reduce the risk of death. It can be given in a chewable form or as a rectal suppository.
• Nitroglycerin: This medicine can be quickly absorbed under the tongue and can help widen the coronary arteries and ease chest pain. But it doesn’t reduce the risk of death. A common side effect is a headache. In certain types of heart attacks, nitroglycerin should not be used due to the risk of low blood pressure. Also, it shouldn’t be used if the patient has recently used medications like sildenafil, vardenafil, or tadalafil, as the combination can cause dangerously low blood pressure.
• Oxygen: This should only be used if the blood oxygen level is below 90%. A study found that in non-oxygen-deficient heart attack patients, extra oxygen might increase heart damage and was linked to larger heart attacks after six months.
• Antiplatelet agents: Medications like clopidogrel or ticagrelor can help prevent clots.
• GPIIB/IIIa inhibitors: These are not commonly used nowadays due to the risk of bleeding.
• Beta-blockers: These medications, which can help to lower heart rate and blood pressure, should be started within 24 hours.
• ACE inhibitors or angiotensin receptor blockers (ARBs): These medications can help to relax blood vessels, and should also be started within 24 hours in stable patients.
• Statin: This type of medication, which can help to lower cholesterol levels, should be begun as soon as possible.
• Anticoagulation: Heparin, an anticoagulant medication to prevent new clots from forming, is required after thrombolysis. Other agents like low molecular weight heparin, fondaparinux, and bivalirudin may also be options.

What else can Posterior Myocardial Infarction (Heart Attack) be?

When diagnosing chest pain, doctors consider a wide range of possibilities. The actual cause is narrowed down by reviewing the patient’s medical history, conducting physical exams, and possibly performing other tests.

There are certain critical conditions associated with chest pain that need immediate attention. Often referred to as the “6 deadly causes of chest pain,” these include:

• Acute coronary syndromes: Severe, sudden heart conditions such as heart attacks
• Aortic dissection: Serious, life-threatening condition involving the major artery from the heart
• Pulmonary embolism: Blood clot in the lungs
• Cardiac tamponade: build-up of fluid around the heart, preventing it from working properly
• Tension pneumothorax: air build-up in the space around the lungs, leading to lung collapse
• Esophageal perforation (Boerhaave syndrome): A tear in the tube that connects your throat and stomach

Other non-critical but urgent diagnoses may include:

• Conditions of the heart lining, like pericarditis and myocarditis
• Conditions related to the lungs, such as pneumomediastinum, pneumothorax, hemothorax, Asthma, COPD, and pneumonia
• Different types of angina or chest pain caused by reduced blood flow to the heart
• Certain gut issues like cholecystitis, pancreatitis, GERD, peptic ulcer, esophageal spasm, and biliary colic
• Musculoskeletal conditions causing chest pain
• Chest pain related to fractures, Herpes zoster, and psychological causes

The list of potential causes of chest pain is extensive, and it’s important that physicians evaluate these possibilities to reach an accurate diagnosis.

What to expect with Posterior Myocardial Infarction (Heart Attack)

Diagnosing a posterior myocardial infarction can be challenging because the changes usually seen in an EKG (a test that measures heart activity) aren’t as noticeable compared to other types of heart issues. Yet, even if this starts to affect the back of the heart, the risk of death isn’t typically different compared to other forms of this condition.

If patients experience a severe form of this condition, known as STEMI, and receive a treatment called PCI within two hours, the likelihood of dying within 30 days is between 3% and 5%. But if the damage extends from the bottom or side of the heart to the back, the infarct (the area damaged by lack of oxygen) becomes significantly larger. This could lead to more serious complications like impaired heart function and an increased risk of death.

Possible Complications When Diagnosed with Posterior Myocardial Infarction (Heart Attack)

Myocardial infarction, or a heart attack, can lead to various complications. Arrhythmias, or irregular heart rhythms, are common and can occur early on, usually within the first three days. Risk of another heart attack or an extension of the existing one can happen too. Mechanical complications include various forms of heart ruptures and anomalies, which can be extremely serious. These can lead to heart failure or cardiogenic shock, both of which are severe conditions. There is also an increased risk of embolic events. This can result in peripheral ischemia or stroke because of an inadequate blood supply. Pericarditis, an inflammation of the sac surrounding the heart, can occur too. This condition can appear early or late and when it’s late in onset it’s known as Dressler syndrome or post-cardiac injury syndrome, which is an autoimmune response.

Potential complications of myocardial infarction include:

• Arrhythmias, usually occurring within the first three days
• Increased risk of another heart attack
• Various mechanical complications such as different forms of heart ruptures and anomalies
• Heart failure and cardiogenic shock
• Increased risk of embolic events leading to peripheral ischemia or stroke
• Pericarditis or inflammation of the sac surrounding the heart, which might lead to Dressler syndrome or post-cardiac injury syndrome if it’s late in onset

Preventing Posterior Myocardial Infarction (Heart Attack)

Heart disease is a serious condition that can lead to a high risk of illness and death. It’s important for people with heart disease to be educated about things they can change to lower their risk, like their lifestyle and habits. There are several known risk factors including smoking, diabetes, high blood pressure, and high cholesterol. Other harmful behaviors that can increase the risk of heart disease include being overweight, not getting enough exercise, and being too inactive or sedentary.

It’s also essential that patients are taught to recognize signs that may indicate a heart attack. They need to understand how and when to use their heart medication, like nitroglycerin if it’s been prescribed to them, and know when it’s necessary to call 911 for immediate help.