A heart attack, medically termed a myocardial infarction, occurs when blood flow to a section of the heart muscle is severely reduced or completely cut off. This interruption, typically caused by a blood clot forming over a ruptured plaque in a coronary artery, deprives the muscle of oxygen and causes tissue death. While a change in heart rate is common during such an event, no single beats-per-minute (BPM) number definitively diagnoses a heart attack. Heart rate changes are secondary effects resulting from the underlying cardiac distress, not the primary diagnostic criteria.
Why Heart Rate is Not a Definitive Indicator of a Heart Attack
A heart attack is fundamentally a problem of plumbing (an obstructed artery), but the resulting heart rate change is an electrical issue. The lack of oxygen delivery, known as ischemia, irritates heart muscle cells, leading to electrical instability. This instability can trigger an abnormal rhythm, or arrhythmia, which manifests as a noticeable change in heart rate.
The resulting heart rate depends entirely on the location and severity of the blockage. If the blockage supplies the heart’s natural pacemaker (the sinoatrial or atrioventricular node), the rhythm can slow dramatically, resulting in an abnormally low rate. Conversely, the body’s stress response to pain and lack of blood flow releases adrenaline, which can cause the heart to beat excessively fast to compensate.
The heart may also continue to beat within a normal range if the damage is confined to an area that does not disrupt the main electrical conduction pathways. Relying solely on a heart rate reading provides an incomplete and potentially misleading assessment of the cardiac crisis. Physicians rely on diagnostic tools like the electrocardiogram (ECG) and blood tests for cardiac biomarkers, which directly measure electrical activity and muscle damage.
Defining Abnormal Heart Rates in a Cardiac Context
For a healthy adult at rest, the typical heart rate range is between 60 and 100 beats per minute (BPM). Rates outside this standard range are classified into two main categories of rhythm disturbance. These definitions provide context for abnormal heart activity but are not specific to a heart attack.
A heart rate below 60 BPM is defined as bradycardia. Tachycardia is defined as a heart rate exceeding 100 BPM at rest. While a heart attack can precipitate these rhythms, both conditions can also be triggered by numerous other factors.
For example, dehydration or fever can lead to temporary tachycardia, and a high level of physical fitness can result in resting bradycardia. The presence of an abnormal heart rate serves as a general sign of cardiac stress but is insufficient evidence to isolate a heart attack as the cause.
Recognizing the Physical Symptoms
Since heart rate is an unreliable indicator, the most important information involves recognizing the physical symptoms that signal a life-threatening event. The classic presentation involves crushing chest pain or pressure that feels like a weight sitting on the chest. This intense discomfort often lasts for more than a few minutes or may repeatedly subside and return.
The pain frequently radiates outward from the chest to other areas of the upper body, extending down one or both arms, into the back, the neck, or the jaw. These classic symptoms are the most direct signal of myocardial distress and require immediate attention. However, a heart attack does not always present with dramatic chest pain.
Atypical symptoms are common in women, the elderly, and individuals with diabetes. These subtle signs must not be dismissed and can include:
- Extreme fatigue, which may feel sudden or inexplicable.
- Unexplained shortness of breath.
- Nausea.
- Vomiting.
- A cold sweat.
- Lightheadedness.
For many, the discomfort may feel more like indigestion or generalized upper back and shoulder pain rather than sharp chest pain.
Immediate Emergency Response Protocol
If any critical physical symptoms are present, the immediate action is to call 911 or the local emergency medical service number. Emergency medical services personnel can begin administering life-saving treatment and monitoring the heart rhythm en route, which significantly reduces the time to definitive care. Do not attempt to drive oneself or the affected person to the hospital, as the heart could suddenly stop beating during transport.
The person should sit down and rest quietly to minimize the heart’s oxygen demand until help arrives. If the person is not allergic to aspirin, has no medical condition that prevents its use, and is advised by the emergency operator, chewing a regular-strength aspirin (325 mg) or four low-dose aspirins (81 mg each) can be beneficial. Aspirin helps inhibit blood clotting and can reduce the extent of damage to the heart muscle.