Myocardial infarction This is the usual medical term for what is commonly called a heart attack, coronary thrombosis,or,simply,coronary.The various terms are interconnected, and represent different ways of looking at slightly different things. Myocardial infarction describes the area of damage in the heart resulting from loss of its blood supply.Coronary thrombosis refers to clotting in a coronary artery.This is the usual cause of a myocardial infarction,but the arterial blockage could more rarely be due to a blood clot that travelled from elsewhere an embolus.Heart attack refers to a sudden cardiac problem that is often a myocardial infarction due to a coronary thrombosis.However,in some cases the heart attack may lead to an immediate cardiac arrest.Cardiac output suddenly stops, because of either asystole or ventricular fibrillation,and the patient literally drops dead,long before permanent damage has been done to the heart.It is difficult to resuscitate someone with asystole -complete absence of electrical or mechanical activity in the heart -but ventricular fibrillation can often be reversed by cardiac resuscitation.In ventricular fibrillation,the ventricles contract feebly around 500 times a minute,and no useful output is produced,just as if the heart had suddenly stopped beating.Provided life is maintained by immediate external cardiac massage and artificial ventilation,the application of a defibrillating electrical current through the chest can cause the heart to resume sinus rhythm.The patient can then be investigated and treated for the myocardial infarction that is likely to be present. After the interruption of its blood supply,and provided there is no cardiac arrest,the myocardium continues to beat and rapidly accumulates a severely adverse metabolic state.Pain fibres carried with the sympathetic nerves are stimulated. Feeling an intense pain in the centre of the chest,where the heart is known to lie, often gives a feeling of impending death.Severe pain from any source leads toreflex effects,including nausea and vomiting,pallor and sweating and autonomic disturbances of heart rate,either slow (bradycardia)or fast (tachycardia).If
Myocardial infarction This is the usual medical term for what is commonly called a heart attack, coronary thrombosis, or, simply, coronary. The various terms are interconnected, and represent different ways of looking at slightly different things. Myocardial infarction describes the area of damage in the heart resulting from loss of its blood supply.Coronary thrombosis refers to clotting in a coronary artery. This is the usual cause of a myocardial infarction, but the arterial blockage could more rarely be due to a blood clot that travelled from elsewhere - an embolus. Heart attack refers to a sudden cardiac problem that is often a myocardial infarction due to a coronary thrombosis. However, in some cases the heart attack may lead to an immediate cardiac arrest. Cardiac output suddenly stops, because of either asystole or ventricular fibrillation, and the patient literally drops dead, long before permanent damage has been done to the heart. It is difficult to resuscitate someone with asystole - complete absence of electrical or mechanical activity in the heart - but ventricular fibrillation can often be reversed by cardiac resuscitation. In ventricular fibrillation, the ventricles contract feebly around 500 times a minute, and no useful output is produced, just as if the heart had suddenly stopped beating. Provided life is maintained by immediate external cardiac massage and artificial ventilation, the application of a defibrillating electrical current through the chest can cause the heart to resume sinus rhythm. The patient can then be investigated and treated for the myocardial infarction that is likely to be present. After the interruption of its blood supply, and provided there is no cardiac arrest, the myocardium continues to beat and rapidly accumulates a severely adverse metabolic state. Pain fibres carried with the sympathetic nerves are stimulated. Feeling an intense pain in the centre of the chest, where the heart is known to lie, often gives a feeling of impending death. Severe pain from any source leads toreflex effects, including nausea and vomiting, pallor and sweating and autonomic disturbances of heart rate, either slow (bradycardia) or fast (tachycardia). If
damage to the heart is extensive,the heart may be unable to maintain an adequate resting cardiac output (central circulatory failure).The patient will then be pale, with cold peripheries because of compensatory vasoconstriction,blood pressure falls and urgent treatment is needed.Diuretics reduce circulating blood volume and hence reduce the load on the weakened heart.Occasionally,dramatic mechanical complications develop -the damaged heart wall may rupture into the pericardial cavity,which fills up and prevents adequate cardiac filling and hence pumping.Or the interventricular septum may break down,leading to a ventricular septal defect. The fundamental treatment for myocardial infarction is to deal as rapidly as possible with its cause,i.e.unblock the offending coronary artery.Time is of the essence.Fortunately,patients with sudden severe cardiac pain usually seek medical attention promptly.If the artery can be unblocked within an hour or so,there is a good chance that there will be little permanent damage.But if the artery remains blocked for more than 6 hours,the damaged myocardium has probably passed the point of no return.Between these limits,the myocardium may make a fairly good recovery over the next few months,during which the heart is vulnerable and should be protected from avoidable stress,such as non-urgent surgery and anaesthesia. Treatment consists of giving intravenously a plasminogen activator.This is a substance that mimics the normal action of a fibrin clot in the body by converting circulating plasminogen into plasmin,a proteolytic enzyme that effectively digests and breaks down the recent fibrin clot.Unfortunately,this thrombolytic therapy can also break down recent thrombus that may be usefully sealing a leaky vessel,especially in an elderly patient.If this leaky vessel is in the brain, bleeding may lead to a stroke,illustrating once more that potent beneficial treatment is capable of severe adverse effects. Similar treatment can sometimes be given for clotting in other sites,including leg vessels.However,since the onset of the clotting is rarely as clear as with a coronary occlusion it is harder to ensure treatment within the short window of opportunity.Sadly,thrombolytic therapy is rarely helpful for patients with strokes
damage to the heart is extensive, the heart may be unable to maintain an adequate resting cardiac output (central circulatory failure). The patient will then be pale, with cold peripheries because of compensatory vasoconstriction, blood pressure falls and urgent treatment is needed. Diuretics reduce circulating blood volume and hence reduce the load on the weakened heart. Occasionally, dramatic mechanical complications develop - the damaged heart wall may rupture into the pericardial cavity, which fills up and prevents adequate cardiac filling and hence pumping. Or the interventricular septum may break down, leading to a ventricular septal defect. The fundamental treatment for myocardial infarction is to deal as rapidly as possible with its cause, i.e. unblock the offending coronary artery. Time is of the essence. Fortunately, patients with sudden severe cardiac pain usually seek medical attention promptly. If the artery can be unblocked within an hour or so, there is a good chance that there will be little permanent damage. But if the artery remains blocked for more than 6 hours, the damaged myocardium has probably passed the point of no return. Between these limits, the myocardium may make a fairly good recovery over the next few months, during which the heart is vulnerable and should be protected from avoidable stress, such as non-urgent surgery and anaesthesia. Treatment consists of giving intravenously a plasminogen activator. This is a substance that mimics the normal action of a fibrin clot in the body by converting circulating plasminogen into plasmin, a proteolytic enzyme that effectively digests and breaks down the recent fibrin clot. Unfortunately, thisthrombolytic therapy can also break down recent thrombus that may be usefully sealing a leaky vessel, especially in an elderly patient. If this leaky vessel is in the brain, bleeding may lead to a stroke, illustrating once more that potent beneficial treatment is capable of severe adverse effects. Similar treatment can sometimes be given for clotting in other sites, including leg vessels. However, since the onset of the clotting is rarely as clear as with a coronary occlusion it is harder to ensure treatment within the short window of opportunity. Sadly, thrombolytic therapy is rarely helpful for patients with strokes
It is difficult to be sure that the problem is due to thrombosis rather than haemorrhage,and there is a risk of bleeding in the infarcted area of brain
It is difficult to be sure that the problem is due to thrombosis rather than haemorrhage, and there is a risk of bleeding in the infarcted area of brain