A heart attack, or myocardial infarction, signals a serious blockage of blood flow to the heart muscle, demanding immediate medical attention. While chest pain is the most recognized symptom, pain often radiates into the arm. This specific symptom is common, yet the reason behind it is often confusing. Understanding this connection requires examining how the nervous system processes pain signals from internal organs, which can misdirect the sensation to areas like the arm.
The Phenomenon of Referred Pain
The pain felt in the arm during a heart attack is an example of a neurological concept known as referred pain. This occurs when a painful stimulus originating in a deep organ is perceived by the brain as coming from a different, often distant, part of the body. The phenomenon happens because the internal organs, called viscera, have fewer sensory nerve fibers compared to the skin and skeletal muscles. The brain is therefore not accustomed to receiving precise pain signals from these organs.
When the heart muscle is deprived of oxygen during a heart attack, it sends out distress signals along its visceral sensory nerves. These internal signals enter the spinal cord and converge with signals coming from the body’s surface, such as the arm. Because the brain receives these combined signals through the same pathway, it misinterprets the visceral pain from the heart as somatic pain from the more sensitive area of the arm. The pain is genuine, but its perceived location is incorrect due to this shared neural circuitry.
The Specific Nerve Connection
The specific anatomical reason for this misdirection lies in how the sensory nerves from the heart and the arm enter the spinal cord. Sensory nerves from the heart, which are part of the autonomic nervous system, primarily enter the spinal cord at the upper thoracic segments, specifically T1 through T5. At these same spinal cord levels, the sensory nerves that innervate the chest wall, shoulder, and the inner side of the left arm also enter the cord.
Both the heart and the arm share the same second-order neurons in the spinal cord that carry the pain message up to the brain. When the heart experiences a lack of oxygen, the resulting pain signal travels to the T1-T5 spinal levels. Because the spinal neurons are accustomed to carrying sensory information from the arm and shoulder, the brain projects the pain back to that familiar area. This is why the pain is most frequently felt radiating down the left arm, though it can also affect the right arm or both arms.
Other Critical Heart Attack Symptoms
While arm pain is a well-known symptom, a heart attack includes a larger clinical picture that may involve various other signs of distress. The most common symptom for both men and women is discomfort in the chest, often described as a crushing pressure, squeezing, or fullness that lasts more than a few minutes or goes away and comes back. This chest discomfort may radiate not only to the arm but also to the jaw, neck, back, or stomach.
Symptoms can vary significantly between individuals, and women are more likely to experience less traditional symptoms. These symptoms often include:
- Unusual fatigue
- Sleep disturbance
- Nausea or vomiting
- Pain in the back or jaw
- Shortness of breath
- Breaking out in a cold sweat
- Feeling lightheaded and dizzy
Because a heart attack is a medical emergency, anyone experiencing these symptoms should seek immediate emergency medical help.