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Q: I thought heart attacks are caused by sudden complete blockage in a heart artery. But my father’s happened because his blood pressure suddenly got too low. Are there different types of heart attacks?

A: Yes, there are different types of heart attacks. Most often the underlying problem is the same. One or more of the coronary arteries (the vessels that supply blood to the heart) have some or often a lot of fatty plaque buildup. During a heart attack, not enough oxygen-rich blood — or none at all — gets delivered to an area of the heart.

There are two different mechanisms that cause this compromised blood flow. Doctors define them as type 1 and type 2 heart attacks. The distinction is important because they may be treated differently.

Type 1 heart attacks: With a type 1 heart attack, the cap over a plaque deposit ruptures and releases chemicals that trigger the formation of a blood clot. The clot blocks the artery, interfering with blood flow to part of the heart.

Type 2 heart attacks: A type 2 heart attack does not involve a ruptured plaque. Instead, it happens when there is a mismatch between the amount of blood a portion of the heart muscle needs and the blood supply in the coronary artery feeding that area of the heart.

The trigger for a type 2 heart attack can be a condition that puts extra stress on the heart, like the flu or pneumonia, an abnormal heart rhythm resulting in an accelerated heart rate, or a sudden drop in blood pressure.

With any concern for a heart attack, the doctor will immediately order an electrocardiogram (ECG) and a blood test to measure levels of troponin, a protein in heart muscle cells that spills into the bloodstream when any type of heart damage occurs.

Doctors look for high troponin levels and certain changes in the electrical pattern on the ECG to make a diagnosis. Both tests are used because either one can be normal or show only minimal changes in the earliest stage of a heart attack.

In fact, even with normal ECG and troponin results, emergency department doctors will begin immediate treatment if your symptoms are highly suggestive of a heart attack, especially if you have multiple heart risk factors.

If you’re diagnosed with a likely type 1 heart attack, the doctor will probably send you to the cardiac catheterization lab for angioplasty and stent placement to restore blood flow to the injured heart muscle and minimize permanent damage.

For a type 2 diagnosis, the goal is to improve the balance between blood supply and demand. It’s important to address any medical problem that stresses the heart, such as an infection, an abnormally fast heart rhythm, or low blood pressure.

Q: My brother was diagnosed with an aortic aneurysm. Do I need to be tested to see if I have one?

A: The aorta is the thick-walled vessel that carries blood from the heart’s left ventricle to the rest of the body. It curves up and over the heart in a gentle arc, narrowing slightly as it extends down through the center of the body.

As is true for most heart problems, smoking and high blood pressure can heighten the risk of problems with the aorta.

But so can genes and certain medical conditions, which can weaken the wall of the aorta. As a result, the aortic wall may tear (aortic dissection) or bulge outward (aortic aneurysm) and possibly rupture.

About three-quarters of all aortic aneurysms occur in the center of the body, below the kidneys. Known as abdominal aortic aneurysms (AAAs), most grow very slowly and don’t cause any symptoms. But an undiscovered one can expand rapidly and burst with little warning.

Aneurysms in the chest area (thoracic aortic aneurysms, or TAAs) are classified by location.

Those in the descending aorta (the section after the arch of the aorta) are more common in older people who smoke and have high blood pressure.

Aneurysms in the ascending aorta (the section closest to the heart) usually occur in younger people and may be linked to certain genetic conditions, including a bicuspid aortic valve, in which the valve has only two flaps instead of the usual three. About one in every 100 people has a bicuspid aortic valve, and half of them have an enlarged aorta.

You should ask your doctor about getting a screening test to see if you might be developing an aortic aneurysm. But which test you might need depends on the location of your brother’s aneurysm.

Screening for an abdominal aortic aneurysm involves a simple abdominal ultrasound, which the guidelines recommend for people at greatest risk: (1) anyone with a family history of an AAA, and (2) men ages 65 to 75 who have ever smoked.

A heart ultrasound (echocardiogram) or CT scan can be used to screen for a TAA. You should be tested for a thoracic aortic aneurysm if you:

• have a bicuspid aortic valve; have had a bicuspid aortic valve replaced; or have a parent, sibling, or child with one
• have had surgery to replace or repair an aortic valve before age 70
• have a parent, sibling or child who has a thoracic aortic aneurysm or who has experienced a rupture of an aneurysm or an aortic dissection
• have Marfan syndrome, Loeys-Dietz syndrome, vascular Ehlers-Danlos syndrome, Turner syndrome or certain other genetic conditions.

Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, see health.harvard.edu.