What is Acute Myocardial Infarction (Heart Attack)?
Acute myocardial infarction (AMI), commonly known as a heart attack, is one of the leading causes of death in developed countries. It affects nearly 3 million people worldwide, and results in more than 1 million deaths in the United States every year. Heart attacks can be split into two types: non–ST-segment elevation myocardial infarction (NSTEMI) and ST-segment elevation myocardial infarction (STEMI). Unstable angina is similar to an NSTEMI, but it can be identified differently due to normal levels of heart-specific proteins.
A heart attack causes permanent harm to the heart muscle because it doesn’t get enough oxygen. This can alter the way the heart fills with and pumps out blood, and increase the likelihood of irregular heartbeats. It can also lead to a variety of serious health complications. Quickly restoring blood flow to the heart is absolutely critical. Starting treatment within 6 hours of the first symptoms can greatly improve the chances of a better outcome.
A heart attack is identified when 2 of the following signs are seen:
- Symptoms of poor blood supply to the heart.
- New changes in the electrical activity of the heart, or a condition known as a left bundle branch block (LBBB).
- The presence of specific patterns on an electrocardiogram (ECG), known as pathological Q waves.
- New motion abnormalities in the heart wall visible on an imaging study.
- The presence of a blood clot within a coronary artery, identified at autopsy or angiography.
What Causes Acute Myocardial Infarction (Heart Attack)?
Acute myocardial infarction, or a heart attack, happens when the heart doesn’t get enough oxygen because of reduced blood flow due to various reasons. Traditionally, it occurs when something called atherosclerotic plaques – fats deposit on artery walls – rupture and start a clot, which blocks blood flow in the heart arteries. Heart attacks can also be triggered by a blood clot traveling to the heart (coronary artery embolism), which affects about 2.9% of patients. Other causes can include the effects of drug use like cocaine, a tear in the coronary artery, and sudden tightening of the arteries (coronary vasospasm).
There are risk factors for heart attacks that can’t be changed, such as sex, age, family history of heart disease, and male pattern baldness.
But there are also modifiable risks that you can control, including smoking, unhealthy blood lipid levels (dyslipidemia), diabetes, high blood pressure, obesity, not getting enough exercise (sedentary lifestyle), not taking care of your teeth and gums (poor oral hygiene), having peripheral vascular diseases, and having high levels of a substance called homocysteine in the blood.
Other factors causing heart attacks include physical damage to the heart (trauma), inflammation of the blood vessels (vasculitis), use of drugs like cocaine, abnormalities in the heart arteries, blood clots in the heart arteries (coronary artery emboli), an internal tear in the main artery that carries blood out of the heart (aortic dissection), and situations that put extra strain on the heart, like an overactive thyroid (hyperthyroidism) or anemia.
Risk Factors and Frequency for Acute Myocardial Infarction (Heart Attack)
Most fatal heart attacks, about 70%, are caused by blocked arteries due to atherosclerosis, a build-up of plaques in the arteries. Therefore, managing risk factors for atherosclerosis is often key to preventing heart attacks. Lifestyle choices, which are factors we can change, account for 90% of heart attack cases in men and 94% in women. These choices include:
- Smoking cigarettes
- Having a sedentary lifestyle
- Living with high blood pressure
- Being obese
- Having high cholesterol levels, especially LDL (‘bad’ cholesterol)
- Having high triglyceride levels.
However, some risk factors for atherosclerosis and heart attacks can’t be changed. These nonmodifiable risk factors are:
- Age
- Sex
- Family history of heart disease.
Signs and Symptoms of Acute Myocardial Infarction (Heart Attack)
Diagnosing Acute Myocardial Infarction (AMI) or a heart attack may not always be straightforward based on just patient’s history and a physical examination. Doctors aim to understand the symptoms on the onset, their characteristics, and any related symptoms. Research has found that profuse sweating and pain radiating to both arms are often signs of a heart attack in men. Other accompanying symptoms may include:
- Feeling lightheaded
- Anxiety
- Cough
- Having a sensation of choking
- Profuse sweating
- Wheezing
- An irregular heart rate
A physical check-up would involve measuring the patient’s vital signs and observing the patient’s overall appearance, heart, and lung function. Particular aspects of the examination might include:
- Heart rate: A fast heart rate, atrial fibrillation (irregular heart rhythm), or ventricular arrhythmia (serious heart rhythm disturbance) might be present, signaling problems with the heart’s electrical system.
- Pulses: If the patient’s pulses are noticeably different between limbs, it could mean an issue such as aortic dissection, an arterial problem.
- Blood pressure: Although high blood pressure is common in AMI cases, it may drop if the patient’s heart isn’t pumping enough blood (shock) due to the heart muscle damage.
- Respiratory findings: Quick breaths and fever could be signs of an inflammation response.
- Neck veins: Swollen neck veins could indicate right heart failure and increased blood pressure in the veins.
- Cardiac findings: The heart’s position might have changed, and there might be sound irregularities in the heartbeats, and an abnormal heart sound (murmur) due to damaged heart valves. A particular type of loud, lasting heart murmur that spreads to the breastbone could mean a hole in the heart wall.
- Pulmonary findings: Wheezing and crackling sounds from the lungs could mean fluid buildup in the lungs.
- Extremities: Swollen or blue limbs might indicate that the circulation is poor, and can also feel cold to touch.
Testing for Acute Myocardial Infarction (Heart Attack)
An electrocardiogram (ECG) is a routine test that doctors use when patients come in with chest pain. Sometimes, women and older patients may experience different symptoms, like a stomach ache, dizziness, or shortness of breath. These symptoms should also result in an ECG test.
Although the ECG is very accurate (95-97%) when it comes to diagnosing a heart attack (myocardial infarction, or MI), it is not of much help in excluding a heart attack because of its low sensitivity rate of 30%. Changes in the ECG such as peaked T-waves or ST-elevation could suggest early heart damage. But ECG’s can be harder to interpret in patients with existing heart diseases or ones using pacemakers.
If a person has symptoms of a heart attack but their ECG doesn’t necessarily agree, doctors may look for non-ST-elevation myocardial infarction (NSTEMI). This refers to a type of heart attack that doesn’t cause major changes in an ECG but causes damage nonetheless. Doctors often look for changes in the heart’s electrical activity over time and use diagnostic guides to find patients who may have an NSTEMI.
Because ECG’s aren’t perfect at detecting all heart attacks, doctors often test for a protein called troponin in the blood, which increases when the heart is damaged. The HEART score is a measure that doctors can use to estimate the risk of a heart attack by combining the doctor’s suspicion, the patient’s risk factors, ECG findings, and troponin levels.
Certain lab tests are routinely done when a heart attack is suspected. Primary among these is the troponin test but tests for creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH), along with complete blood counts and metabolic panels, are also often done.
Gauging the levels of these different proteins can provide doctors a clearer understanding of an ongoing heart attack. For instance, troponin levels peak at 12 hours and remain raised for about a week. Then, there’s a substance called high-sensitivity troponin, which is more sensitive than standard troponin, but it may also yield many false-positive results. CK-MB levels peak at 10 hours and return to normal in two to three days. Finally, LDH levels peak after 72 hours and return to normal within 10 to 14 days.
Furthermore, imaging techniques such as cardiac angiography and echocardiography can aid in the diagnosis of a heart attack. Cardiac angiography is used to identify blockages in the blood vessels of the heart, and an echocardiogram is used to evaluate the motion of the heart wall, the degree of valve abnormality, and to check for other complications.
Treatment Options for Acute Myocardial Infarction (Heart Attack)
All patients suffering from heart attacks should immediately be given a chewable aspirin. The dose should be between 162 mg and 325 mg. They should also have an IV line put in place. If their oxygen levels drop below 91%, oxygen should be provided. For controlling pain, drugs like sublingual nitroglycerin can be given if their blood pressure is in the safe range. Opioids might also be used for the same.
The main treatment goal for a type of heart attack called STEMI is to restore blood flow immediately. Ideally, this is done using a technique called PCI. Before this, patients are given a combination of blood-thinning drugs including heparin and ticagrelor. Other agents that prevent clotting could also be used during PCI. If PCI can’t be performed within 90 minutes of a STEMI diagnosis, a clot-busting drug should be given.
For patients with another type of heart attack, NSTEMI, who are stable and show no symptoms, medication is usually the first approach. These medications include antiplatelet drugs among others. However, if needed, PCI can be done within 48 hours of hospital admission. Doing this could potentially improve patient survival and reduce hospital stay.
If patients with NSTEMI have constant chest pain or other serious symptoms, emergency PCI is needed.
Before they are sent home, patients who have had a heart attack may be given prescriptions for aspirin, a cholesterol-lowering medicine (a high-dose statin), a beta-blocker, and sometimes an ACE inhibitor.
If PCI is chosen as the treatment for a heart attack, it should ideally be done within 12 hours of experiencing symptoms. If a drug that can dissolve clots is chosen as the main strategy for restoring blood flow, it should be given within 120 minutes. In all heart attack patients, additional blood-thinning therapy is recommended regardless of whether they undergo PCI or get a clot-busting treatment.
What else can Acute Myocardial Infarction (Heart Attack) be?
When determining if a person has an Acute Myocardial Infarction (AMI), or heart attack, doctors also consider other health conditions that have overlapping symptoms:
- Aortic dissection: This severe condition involves a tear in the aorta’s inner layer. It can cause the aorta’s layers to separate and potentially impede blood flow.
- Pericarditis: This condition is an inflammation of the pericardium, a protective layer around the heart. Its main symptom, chest pain, can mimic those of an AMI.
- Acute gastritis: In this condition, the stomach lining becomes inflamed, causing upper abdominal pain that might be mistaken for chest pain related to the heart.
- Acute cholecystitis: This inflammation of the gallbladder results in pain in the upper right section of the abdomen. The pain can radiate to the chest, similar to heart-related symptoms.
- Asthma: Intense asthma attacks can cause difficulty breathing, wheezing, and chest tightness, which could be confused for heart-related symptoms.
- Esophagitis: This inflammation of the esophagus can cause chest discomfort, especially if it’s linked to gastroesophageal reflux disease (GERD) or other esophageal disorders.
- Myocarditis: This condition is inflammation of the heart muscle, which can cause chest pain and produce symptoms similar to a heart attack.
- Pneumothorax: Also known as a collapsed lung, this can result in sudden chest pain and difficulty breathing – similar to symptoms experienced with heart-related issues.
- Pulmonary embolism: This condition occurs when a blood clot travels and blocks a lung artery. This can cause chest pain and shortness of breath, which might resemble a heart attack.
Doctors need to rule out these possibilities to correctly diagnose and treat an AMI.
What to expect with Acute Myocardial Infarction (Heart Attack)
Acute myocardial infarction (AMI), also known as a heart attack, carries a significant risk of death, especially outside of the hospital. Statistics show that about one-third of patients unfortunately pass away before reaching the hospital. Additionally, around 40% to 50% do not survive upon arrival. What’s more, another 5% to 10% of patients may pass away within the first year following a heart attack.
The likelihood of recovering from a heart attack largely depends on the extent of the heart muscle damage. Patients who get treatment right away, including therapies to restore blood flow within the first 30 minutes to 90 minutes of arrival at the hospital, generally have better outcomes. Similarly, patients with a preserved ejection fraction—which refers to how well your heart pumps blood—have a better prognosis than those with a reduced ejection fraction.
Proper medical care after a heart attack is crucial for improving long-term survival. Standard practices include starting on medications like aspirin, beta-blockers, and ACE inhibitors, all of which help prevent recurring heart problems.
Several factors can worsen prognosis, including age, diabetes, having had a heart attack previously, having vascular disease or stroke, delayed treatment, reduced ejection fraction, congestive heart failure, high levels of inflammation (measured by C-reactive protein) and B-type natriuretic peptide (BNP), and depression.
Roughly 50% of patients end up being readmitted within the first year after their initial heart attack. The overall prognosis depends on factors like the ejection fraction, age, and other medical conditions. Generally, patients who’re unable to have procedures to restore blood flow have poorer outcomes than those who can. The best prognosis is usually seen in patients with early and successful treatment and preserved heart pumping function.
Possible Complications When Diagnosed with Acute Myocardial Infarction (Heart Attack)
The main complications that can occur after an Acute Myocardial Infarction (AMI), or heart attack, include:
- Developing a new kind of heart murmur (new-onset mitral regurgitation)
- A tear in the wall that separates the two large chambers of the heart (ventricular septal rupture)
- Ballooning out, or an aneurysm, of the left chamber of the heart (left ventricular aneurysm)
- Heart rhythm problems (arrhythmias)
- Clots traveling through the bloodstream (emboli)
Recovery from Acute Myocardial Infarction (Heart Attack)
Cardiac rehabilitation significantly helps in a patient’s recovery after a heart attack (AMI). Studies have pointed out the many advantages of this, such as improved quality of life, less disability and lower chances of dying.
The rehab process needs to be tailored to each patient, taking into account their specific needs, available resources, set goals and physical abilities before and after the heart attack. Working together, rehab therapists and the overall care team play a crucial role in providing uninterrupted care.
Besides helping with recovery, cardiac rehab has been seen to reduce the risk of future heart or blood vessel related incidents. Yearly check-ups indicate that cardiac rehab can lessen the likelihood of future cardiovascular problems.
Preventing Acute Myocardial Infarction (Heart Attack)
Here are some recommended steps to take if you think you might be having a heart attack, also known as an Acute Myocardial Infarction (AMI):
If you’re feeling symptoms that might suggest a heart attack, such as chest pain, trouble breathing, feeling sick or feeling light-headed, it’s crucial that you seek medical help immediately. Don’t hesitate – make your way to the emergency room as quickly as you can.
If you’ve taken nitroglycerin (a medication often used to treat chest pain) but you’re not feeling any better, you should call for emergency help right away.
Adopting a diet low in salt could also be helpful, especially in managing high blood pressure. This could also reduce the strain on your heart.
Join a cardiac rehabilitation program. These are designed to provide support and guidance for individuals recovering from heart-related conditions, including AMI.
Stop smoking right away. Indeed, smoking is a major risk factor for developing heart and blood vessel diseases.
It’s also very important to take any prescribed medication as instructed by your doctor.