Myocardial infarction

• 1. Introduction

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  Myocardial infarction strikes about 15.9 million people worldwide every year, yet the image most people carry of a heart attack is almost entirely wrong. Popular media tends to show someone collapsing dramatically, losing consciousness, falling to the floor. In reality, chest pain that quietly builds over more than 20 minutes, a jaw that aches for no clear reason, or an arm that simply feels wrong can all be the first signal that the heart's blood supply has been cut off. Women face an extra layer of confusion: their most common warning signs are shortness of breath, weakness, and unusual tiredness, symptoms that are easy to dismiss as something far more ordinary. Among people over 75, roughly 5% have already had a heart attack and never knew it at all.

  At its core, a myocardial infarction is tissue death. When blood flow through one of the coronary arteries decreases or stops, the heart muscle that artery feeds begins to die, and those cells do not come back. A collagen scar forms in their place. What follows is a cascade that can touch the heart's electrical system, its structural walls, and its ability to pump. The questions that matter are: what causes an artery to block in the first place, how does the medical system race to restore flow before the damage becomes permanent, and why does a person's ZIP code or income level still determine whether they survive?

• 2. The Blocked Artery

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  Atherosclerosis is the slow accumulation, typically over decades, of cholesterol and fibrous tissue within the walls of the coronary arteries. Inflammatory cells, particularly macrophages, move into those walls and gradually become laden with LDL cholesterol, transforming into what pathologists call foam cells. As foam cells die, a cholesterol core forms. Smooth muscle cells migrate in and begin to stabilize the growing mass. In time, a stable plaque may develop a thick fibrous cap, sometimes calcified.

  The danger arises when that cap thins or breaks. Exposed to the pressure of blood flow, a plaque with a thin lining can rupture in minutes. The cholesterol crystals inside have been linked to rupture through both mechanical injury and inflammation. Once the surface tears open, the blood-clotting system responds to the breach, and a thrombus can form fast enough to seal the artery entirely. Cells in the area just below the heart's inner surface, the subendocardial region, are the first to suffer; tissue there begins to die within 15 to 30 minutes of losing its blood supply. The initial wave of infarction can spread over 3 to 4 hours.

  Not every heart attack traces back to plaque rupture. Coronary artery spasm can also block flow, sometimes triggered by cocaine, by extreme cold, or by severe emotional stress, a pattern known as Takotsubo syndrome or broken heart syndrome. Fever, a fast heart rate, hyperthyroidism, anemia, and low blood pressure can tip the balance in a heart already working with a limited supply. Kawasaki disease can also produce a myocardial infarction as a late consequence, a reminder that the coronary arteries can be damaged through many different routes.

• 3. Who Is at Risk

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  Tobacco smoking appears to account for roughly 36% of coronary artery disease cases, making it the single most important modifiable risk factor. Obesity accounts for around 20%, and physical inactivity has been linked to somewhere between 7 and 12% of cases. Job stress and chronic high stress levels together explain perhaps 3% of cases, a smaller share than is often assumed but still measurable.

  Genetics shape risk in ways that no lifestyle change can fully correct. Genome-wide association studies have identified 27 genetic variants tied to elevated myocardial infarction risk. The strongest single association points to chromosome 9, on the short arm at locus 21, a region containing the genes CDKN2A and 2B. Notably, the single nucleotide polymorphisms implicated there sit within a non-coding region, meaning the mechanism is not straightforward. Family history carries independent weight: having a male first-degree relative who had a heart attack before 55, or a female first-degree relative before 65, raises a person's own risk.

  Some risk factors sit outside the familiar lists. Endometriosis in women under 40 is a documented risk factor. Short-term exposure to air pollution, specifically carbon monoxide, nitrogen dioxide, and sulfur dioxide, has been associated with acute cardiovascular events; every 30-unit increase in the Pollutant Standards Index correlated in one analysis with an 8% higher risk of out-of-hospital cardiac arrest on the day of exposure. Even the shift to daylight saving time has been linked in one analysis to a brief spike in heart attacks. Heart attacks also cluster in the morning, occurring at least three times more often between 6 AM and noon than in the late evening.

• 4. Reading the Signals

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  Troponin, a protein released into the bloodstream when heart muscle is injured, has become the cornerstone of diagnosis. A rise in troponin begins within 2 to 3 hours of injury and peaks within 1 to 2 days. One high-sensitivity cardiac troponin test can rule out a heart attack when combined with a normal ECG. CK-MB, an older test, is no longer preferred because it is less specific for acute injury and can be elevated after past cardiac surgery or electrical cardioversion.

  The electrocardiogram adds a different kind of evidence. Electrodes placed on the chest record the heart's electrical activity, and the resulting waveform can reveal an ST segment that has risen above its normal position, new Q waves, or changes in the shape of T waves. A rise in the ST segment in leads V2 and V3 requires at least 2 mm, or 0.2 mV, in men and at least 1.5 mm, or 0.15 mV, in women to meet diagnostic criteria. That distinction matters because ST elevation determines the classification: a STEMI, which makes up roughly 25 to 40% of all myocardial infarctions, triggers a different and more urgent treatment pathway than an NSTEMI.

  Silent heart attacks, where no symptoms are felt at all, account for between 22 and 64% of all infarctions by some estimates. They are more common in older people, in those with diabetes, and in people who have had a heart transplant. In the transplanted heart, the donor organ is not fully connected to the recipient's nervous system, so the normal pain signals never arrive. These cases often surface only later, through a routine ECG, a blood enzyme test, or at autopsy.

• 5. The Race Against Time

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  Aspirin given immediately to someone with a suspected heart attack is known to reduce mortality associated with acute myocardial infarction by at least 50% by shrinking the clot and slowing further clotting. P2Y12 inhibitors such as clopidogrel, prasugrel, and ticagrelor are added concurrently. Prasugrel and ticagrelor are favored in European and American guidelines because they act more quickly and more consistently than clopidogrel.

  For a STEMI, the preferred treatment is primary percutaneous coronary intervention, known as PCI, ideally performed within 90 to 120 minutes of contact with a medical provider. In PCI, small probes travel through peripheral blood vessels, often the femoral or radial artery, to reach the blocked coronary artery. Tiny balloons drag the clot away or stents are inserted to hold the vessel open. When PCI cannot be delivered within that 90 to 120 minute window, fibrinolysis takes over: medications including tissue plasminogen activator, reteplase, streptokinase, and tenecteplase activate the enzymes that dissolve clots. Fibrinolysis carries its own risks, particularly intracranial bleeding, and is not appropriate for patients who have had recent strokes or severe hypertension.

  For people with NSTEMI, heparin is a standard choice, and PCI is added for those considered high risk, ideally within 1 to 3 days. In cases where multiple coronary arteries are blocked and the patient also has diabetes, coronary artery bypass surgery may be preferred over angioplasty. Beta blockers such as metoprolol or carvedilol are started within 24 hours, and ACE inhibitor therapy follows, both continued long-term at the highest dose tolerated. Statins are added to lower LDL cholesterol and reduce the chance of a future event.

• 6. Survival and Its Inequalities

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  In the developed world, the risk of dying after a STEMI has fallen to around 10%. In the United States specifically, between 5 and 6% of STEMI patients die before leaving the hospital, and 7 to 18% die within a year. Without any treatment, roughly a quarter of those affected die within minutes and about 40% within the first month. In 2011, myocardial infarction ranked among the five most expensive conditions for inpatient hospital stays in the US, with costs reaching approximately 11.5 billion dollars across 612,000 hospitalizations.

  But who survives depends on much more than biology. Among people living in low-socioeconomic areas, which represent close to 25% of the US population, heart attacks occurred twice as often as in higher-income areas. Researchers have found that compared to people with graduate degrees, those with lower educational attainment face a higher risk of heart attack, cardiovascular death, and overall mortality. In 2018, many lawfully present immigrants who were eligible for health coverage remained uninsured because of fear, confusion about eligibility, and difficulty navigating enrollment systems, and uninsured undocumented immigrants remained ineligible for coverage entirely. Delays in reaching emergency care because of lack of insurance or financial concern can significantly worsen outcomes.

  Racial disparities are also documented. African Americans in the US carry a greater burden of myocardial infarction, partly because risk factors are more often unrecognized and untreated at a population level. South Asians, including those who have migrated to other countries, experience higher rates of heart attacks at younger ages, driven largely by a higher prevalence of risk factors earlier in life. Rates of death from cardiovascular disease in the US did fall by almost a third between 2001 and 2011, a meaningful improvement. In India, meanwhile, ischemic heart disease had already become the leading cause of death by 2004, accounting for 1.46 million deaths, or 14% of all deaths that year, and deaths were expected to double over the period from 1985 to 2015.