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Acute Myocardial Infarct (AMI)

Acute myocardial infarct (AMI)

By: Dr Eugene Nwosu MBBS, FACC, FACP, FAHA Chief Medical Director.   

AMI also known as heart attack is one of the presentation of coronary artery disease (CAD). Other manifestation of CAD is

  • Angina,
  • Congestive heart failure,
  • Ventricular tachycardia (abnormal rapid heartbeat)
  • and the catastrophic cardiac arrest (sudden cardiac death).

Definition and Mechanism

  • AMI occurs when the blood supply by the coronary arteries to the heart muscles is totally blocked.
  • If the blockage continues beyond 4 hours the heart muscle dependent on that blood supply dies irreversibly resulting in a completed myocardial infarction.
  • The commonest mechanism of acute myocardial infarct is plaque rupture.
  • Plaque formation in the coronary arteries is the progressive buildup of cholesterol material inside the wall of the arteries resulting in varying degree of blockage.
  • The plaque that usually ruptures is cholesterol rich with thin cap separating it from the blood in the lumen of the vessels.
  • Usual everyday stress can trigger plaque rupture which exposes the cholesterol rich inflammatory debris with the blood resulting in formation of blood clot.
  • This clot may grow quickly in size to totally occlude the blood flow in that segment. The result is acute myocardial infarction or sudden cardiac death (SCD).
  • It should be noted that the plaques that usually cause acute myocardial infarction or SCD are small in size blocking less than 60% of the lumen of the vessel.
  • Such plaques are asymptomatic and do not cause chest pain with usual daily activity. This explains why AMI or SCD may occur in a “healthy” individual with no previous symptoms or signs of CAD.

                     

Important statistics.

  • More than 90% of patients having acute MI will have at least one established CAD risk factor
  • Coronary artery disease accounts for at least 80% of the causes of sudden death in the entire world.
  • SCD is the initial manifestation of AMI affecting 50% of the cases.
  • 50% of the deaths in AMI occur in the first hour of evolution and 80% occur in the first 24 hours

Symptoms of Acute myocardial infarct.

The classic symptoms of AMI are

  • Chest pain and
  • Shortness of breath.

The chest pain can be described as

  • Pressure,
  • Tightness,
  • Heavy weight (elephant) on the chest,
  • Constricting band,
  • Discomfort,
  • Bad indigestion.

Symptoms of Acute myocardial infarct Contd.

  • The pain could come and go or it may become persistent.
  • Some patients with previous symptoms of angina pectoris (defined as chest pain that occurs with activity or effort but relieved with rest) should get concerned if the pattern of chest pain increases in frequency, severity or last longer than 20 minutes.
  • This change in the character of the pain may signal transition to AMI also known as acute coronary syndrome (ACS).
  • The location of the chest pain is anterior chest, midline, left side of chest, jaw, both shoulders, left arm; upper back and upper abdomen.
  • It should be noted that diabetics and elderly people may not report any chest pain.
  • Other symptoms are shortness of breath, sweating, nausea, vomiting, palpitation with rapid heartbeat, dizziness, cough and anxiety.
  • Women are more likely to present with atypical symptoms like flu, SOB, jaw pain, upper back pain, dizziness, nausea and vomiting.

Causes and Risk Factors for AMI.

  • Family history of premature death from heart attack
  • Increased age
  • Male sex
  • High Cholesterol
  • Hypertension
  • Diabetes
  • Obesity
  • Smoking
  • Poor diet
  • Sedentary life style
  • Vascular inflammation

Diagnosis of Acute myocardial infarct.

  • Diagnosis of AMI can be established with a quick history and physical examination by your doctor, electrocardiogram and cardiac biomarkers.
  • Other test available to your cardiologist includes Echocardiogram, Stress test with imaging modality and Cardiac Catheterization.
  • An electrocardiogram (ECG) measures your heart electrical activity and the pattern of the ECG abnormality usually reveals the coronary artery blockage responsible for the AMI.
  • However, the ECG will be normal in up to 30% of cases of AMI. Therefore, normal ECG does not exclude AMI in a patient with a good story.
  • Blood test specific for AMI are Cardiac biomarkers like troponin, myoglobin and CK MB. The initial blood test may be normal depending on the onset of the heart attack and the patients presentation.
  • Therefore, this blood test is done in a series of 3 like every 6 to 8 hrs. In emergency department setting, two sets of cardiac biomarkers should be obtained before excluding any heart attack. In a heart attack, the blood level of troponin increases within 3 to 12 hours from onset of the chest pain, peaks of 24 hours and returns to a normal level over 5 to 14days.
  • An echocardiogram can show the segment of the heart muscle with decreased or absent wall motion which is the hallmark of AMI on an imaging modality.
  • A stress test should not be done in an acute setting during a heart attack and is indeed contraindicated. However, stress test can be done for further assessment following AMI.
  • The result of the stress test will guide further decision like continued medical therapy or use of invasive approach with cardiac catherization and balloon angioplasty and stent.
  • The gold standard for diagnosis of AMI is cardiac catheterization (coronary angiogram). The main disadvantage is that it is invasive (getting into your arteries), expensive and not readily available in most hospitals in some countries like Nigeria.

Treatment of Acute myocardial infarct.

  • The most important point about treatment is early presentation.
  • If you present with AMI to a hospital with expertise and cardiac laboratory facilities within 1 hour of onset of symptom, the myocardial infarction can be aborted with proper treatments.
  • Late presentation after 4hrs will result in residual heart muscle damage even when appropriate treatment and interventions are given.
  • The first treatment for AMI is to chew one adult tablet of aspirin (325mg). Aspirin should not be used if you have allergy to aspirin or has had history of bleeding stomach ulcer.
  • Just taking 325mg of Aspirin can decrease the mortality (death) in heart attack by 25%. For people with aspirin allergy, antiplatelet drug like Clopidogrel can be used in place of aspirin.
  • Clopidogrel can prevent new clots from forming and existing clots from growing.
  • Blood thinners like Heparin is sometimes given especially during cardiac catheterization and interventions.
  • Nitroglycerin can be used to improve chest pain and lower blood pressure in hypertensive patients. It acts by widening the blood vessels.
  • Betablockers are particularly useful in patients with heart attack having high blood pressure and rapid heartbeat. They can help limit the severity of damage to the heart. Following heart attack with heart muscles damage, beta blockers have been show to lower mortality (death).
  • ACE inhibitors used with heart attack can lower blood pressure and mortality in people with heart muscle damage.
  • Pain relievers like morphine will relieve pain and anxiety usually associated with heart attack.
  • PCI(Percutaneous Coronary Intervention) is the best treatment for acute MI when available. For best result, it should be done within 4hrs of onset of symptoms.
  • During PCI, your interventional cardiologist will insert a long thin tube called a catheter through an artery in the wrist or groin to reach the blocked artery.
  • A guide wire is then passed through beyond the area of blockage and a balloon is then brought over the wire and inflated at the blockage site to compress the plaque. This usually restores the blood flow with immediate resolution of chest pain.
  • In most cases a stent mounted on a balloon is deployed at the site to achieve better result. The stent usually made of stainless steel or other metal alloys, function as a scaffold to hold open the inside of the coronary artery. Aspirin and blood thinners like heparin and bivalirudin must be used during the procedure to prevent blood clot forming.

                                     

  • Following successful PCI two antiplatelet agents aspirin and Clopidogrel (a similar medication) must be used for at least one year to prevent blood clot blocking the stent (stent thrombosis) and gradual loss of stent lumen size (stent restenosis).
  • Coronary artery Bypass graft (CABG) surgery becomes necessary when there are too many blockages that cannot be treated with PCI or when there is complication of PCI involving a major artery. The cardiovascular surgeon uses a piece of artery and/or vein to reroute blood around the blockage.
  • The surgeon may be use a vein from the leg, and/or the internal mammary artery found in the chest, and/or the radial artery of the forearm. The vein is attached to the aorta. The supply of blood is then rerouted around the blockage.

What should I do after my heart attack Or Procedure (PCI/CABG)

  • Your cardiologist may recommend cardiac rehabilitation program
  • If you are concerned about your health or depressed you should speak out so that you will get the support or help you need
  • You may need a stress test 6weeks after before returning to your prior job or lifestyle
  • Quit smoking if you are a smoker
  • Take a beta blocker after a heart attack if recommended by your cardiologist.
  • Discuss a cholesterol treatment plan with your physician
  • Take a daily enteric coated aspirin (75mg or 81mg) unless you have allergy or reason to avoid aspirin
  • Keep strict control of diabetes
  • Have control of your blood pressure
  • Follow a heart- healthy diet
  • Begin a regular basic exercise program, mainly walking
  • If you are obese or overweight, just losing 10% of your body weight will decrease your risk
  • Learn how to manage your stress.
  • Have a dentist or dental hygienists clean your teeth at least 2 times a year.
  • Be thankful that God has given you a second chance
  • If you trust your doctor, always follow his recommendations.

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