Heart Attack, What’s happening to our body?

A heart attack (also known as a myocar­dial infarc­tion) is the death of heart mus­cle from the sud­den block­age of a coro­nary artery by a blood clot. Coro­nary arter­ies are blood ves­sels that sup­ply the heart mus­cle with blood and oxy­gen. Block­age of a coro­nary artery deprives the heart mus­cle of blood and oxy­gen, caus­ing injury to the heart mus­cle. Injury to the heart mus­cle causes chest pain and chest pres­sure sen­sa­tion. If blood flow is not restored to the heart mus­cle within 20 to 40 min­utes, irre­versible death of the heart mus­cle will begin to occur. Mus­cle con­tin­ues to die for six to eight hours at which time the heart attack usu­ally is “com­plete.” The dead heart mus­cle is even­tu­ally replaced by scar tissue.

Approx­i­mately one mil­lion Amer­i­cans suf­fer a heart attack each year. Four hun­dred thou­sand of them die as a result of their heart attack.

What causes a heart attack?

Ath­er­o­scle­ro­sis

Ath­er­o­scle­ro­sis is a grad­ual process by which plaques (col­lec­tions) of cho­les­terol are deposited in the walls of arter­ies. Cho­les­terol plaques cause hard­en­ing of the arte­r­ial walls and nar­row­ing of the inner chan­nel (lumen) of the artery. Arter­ies that are nar­rowed by ath­er­o­scle­ro­sis can­not deliver enough blood to main­tain nor­mal func­tion of the parts of the body they sup­ply. For exam­ple, ath­er­o­scle­ro­sis of the arter­ies in the legs causes reduced blood flow to the legs. Reduced blood flow to the legs can lead to pain in the legs while walk­ing or exer­cis­ing, leg ulcers, or a delay in the heal­ing of wounds to the legs. Ath­er­o­scle­ro­sis of the arter­ies that fur­nish blood to the brain can lead to vas­cu­lar demen­tia (men­tal dete­ri­o­ra­tion due to grad­ual death of brain tis­sue over many years) or stroke (sud­den death of brain tissue).

In many peo­ple, ath­er­o­scle­ro­sis can remain silent (caus­ing no symp­toms or health prob­lems) for years or decades. Ath­er­o­scle­ro­sis can begin as early as the teenage years, but symp­toms or health prob­lems usu­ally do not arise until later in adult­hood when the arte­r­ial nar­row­ing becomes severe. Smok­ing cig­a­rettes, high blood pres­sure, ele­vated cho­les­terol, and dia­betes mel­li­tus can accel­er­ate ath­er­o­scle­ro­sis and lead to the ear­lier onset of symp­toms and com­pli­ca­tions, par­tic­u­larly in those peo­ple who have a fam­ily his­tory of early atherosclerosis.

Coro­nary ath­er­o­scle­ro­sis (or coro­nary artery dis­ease) refers to the ath­er­o­scle­ro­sis that causes hard­en­ing and nar­row­ing of the coro­nary arter­ies. Dis­eases caused by the reduced blood sup­ply to the heart mus­cle from coro­nary ath­er­o­scle­ro­sis are called coro­nary heart dis­eases (CHD). Coro­nary heart dis­eases include heart attacks, sud­den unex­pected death, chest pain (angina), abnor­mal heart rhythms, and heart fail­ure due to weak­en­ing of the heart muscle.

Ath­er­o­scle­ro­sis and angina pectoris

Angina pec­toris (also referred to as angina) is chest pain or pres­sure that occurs when the blood and oxy­gen sup­ply to the heart mus­cle can­not keep up with the needs of the mus­cle. When coro­nary arter­ies are nar­rowed by more than 50 to 70 per­cent, the arter­ies may not be able to increase the sup­ply of blood to the heart mus­cle dur­ing exer­cise or other peri­ods of high demand for oxy­gen. An insuf­fi­cient sup­ply of oxy­gen to the heart mus­cle causes angina. Angina that occurs with exer­cise or exer­tion is called exer­tional angina. In some patients, espe­cially dia­bet­ics, the pro­gres­sive decrease in blood flow to the heart may occur with­out any pain or with just short­ness of breath or unusu­ally early fatigue.

Exer­tional angina usu­ally feels like a pres­sure, heav­i­ness, squeez­ing, or aching across the chest. This pain may travel to the neck, jaw, arms, back, or even the teeth, and may be accom­pa­nied by short­ness of breath, nau­sea, or a cold sweat. Exer­tional angina typ­i­cally lasts from one to 15 min­utes and is relieved by rest or by tak­ing nitro­glyc­erin by plac­ing a tablet under the tongue. Both rest­ing and nitro­glyc­erin decrease the heart muscle’s demand for oxy­gen, thus reliev­ing angina. Exer­tional angina may be the first warn­ing sign of advanced coro­nary artery dis­ease. Chest pains that just last a few sec­onds rarely are due to coro­nary artery disease.

Angina also can occur at rest. Angina at rest more com­monly indi­cates that a coro­nary artery has nar­rowed to such a crit­i­cal degree that the heart is not receiv­ing enough oxy­gen even at rest. Angina at rest infre­quently may be due to spasm of a coro­nary artery (a con­di­tion called Prinzmetal’s or vari­ant angina). Unlike a heart attack, there is no per­ma­nent mus­cle dam­age with either exer­tional or rest angina.

Ath­er­o­scle­ro­sis and heart attack

Occa­sion­ally the sur­face of a cho­les­terol plaque in a coro­nary artery may rup­ture, and a blood clot forms on the sur­face of the plaque. The clot blocks the flow of blood through the artery and results in a heart attack (see pic­ture below). The cause of rup­ture that leads to the for­ma­tion of a clot is largely unknown, but con­tribut­ing fac­tors may include cig­a­rette smok­ing or other nico­tine expo­sure, ele­vated LDL cho­les­terol, ele­vated lev­els of blood cat­e­cholamines (adren­a­line), high blood pres­sure, and other mechan­i­cal and bio­chem­i­cal forces.

Unlike exer­tional or rest angina, heart mus­cle dies dur­ing a heart attack and loss of the mus­cle is per­ma­nent, unless blood flow can be promptly restored, usu­ally within one to six hours. While heart attacks can occur at any time, more heart attacks occur between 4:00 A.M. and 10:00 A.M. because of the higher blood lev­els of adren­a­line released from the adrenal glands dur­ing the morn­ing hours. Increased adren­a­line, as pre­vi­ously dis­cussed, may con­tribute to rup­ture of cho­les­terol plaques.

Approx­i­mately 50% of patients who develop heart attacks have warn­ing symp­toms such as exer­tional angina or rest angina prior to their heart attacks, but these symp­toms may be mild and discounted.

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