Myocardial Infarctions NCLEX™ Review

Myocardial Infarctions
NCLEX™ Review

A myocardial infarction (MI) or heart attack continues to be one of the leading causes of morbidity and mortality for the United States. According to the CDC – an MI occurs every 40 seconds here in the United States. Every year they indicate that around 790,000 Americans have a heart attack with over half of them being their first MI.

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Patients who do not live a heart healthy lifestyle increase their risk of developing an atherosclerotic lesion in their blood vessels. An MI occurs when a clot is formed overtime in the coronary arteries which serve the purpose of supplying the heart with blood – which provides the heart with oxygen and nutrients while clearing out waste. These clots can be formed slowly overtime which eventually leads to the diagnosis of CAD (coronary artery disease) or IHD (ischemic heart disease) where patients will present with signs and symptoms suggesting their heart is not getting enough oxygen.

Overtime patients may present with symptoms of angina which describes the signs and symptoms of ischemia in the heart (e.g. chest pain, arm pain, back pain). Patients may present with stable angina which means the symptoms are reproduced consistently after physical exertion which can go away on its own. Unstable angina describe patients experiencing this discomfort for a prolonged period which may present more severely and with little to no physical exertion triggering it. An MI occurs when a significant blockage of blood flow occurs in the heart which causes extreme often irrecoverable necrosis of heart tissues which can trickle down to further complications and potentially death.

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Causes of Myocardial Infarctions

There are many contributing factors that can increase the risk of having a heart attack – many of which can be modified to reduce this risk. Examples of modifiable risk factors includes obesity (BMI > 25), frequent use of artery narrowing drugs and substances (e.g. caffeine, theophyline), diets high in cholesterol (mainly LDL-C), and comorbidities associated with narrowing of blood vessels (e.g. diabetes, hypertension). Uncontrollable factors includes being male, especially African American, and advanced age > 50 years.

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Signs and Symptoms of Myocardial Infarction

Chest pain is a key sign and symptom of patients who are experiencing an MI. This pain may be described as sudden, crushing, radiating, shooting, and with heavy pressure. This chest pain is often described clinically as substernal chest pain. These symptoms may be indicative of other issues (e.g. heartburn, gas, anxiety attack) – so clinicians should be careful when screening for the possibility of a heart attack.

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Patients with enough symptoms may be quickly admitted to the hospital and sent to a catheterization lab to further evaluate their condition and potentially provide treatment. Pain in other areas may help distinguish between other issues versus a heart attack. Examples include jaw pain, left arm pain, and pain in the mid-back or shoulder. Patients experiencing an MI may also experience shortness of breath (labored breathing), nausea and vomiting, sweating, pale cool “dusty” skin, and anxiety. It is important to note that some of these symptoms may go unobserved by certain populations including diabetics and women who either may not consider their condition critical or not feel it at all due to reduced sensation.

Clinical Manifestations of Myocardial Infarctions

When an MI occurs the heart tissue will undergo significant stress as a result of poor blood flow to its cells. This can lead to necrosis of tissues including the cardiac muscles which can release a key protein called troponin which is a gold standard clinical manifestation of patients having a MI. A troponin levels > 0.5 very likely indicates a patient is having a heart attack. Other markers that may be evaluated includes CK, CKmb, and CRP which are not used as frequently for diagnosis.

Patients with suspected MI will also like have an abnormal EKG – which should be assessed immediately upon chest pain complaints. EKG changes are due to damage to the conductive tissue in the heart. This may present as ST elevation which suggests no oxygen supply to the heart or potentially hyperkalemia which becomes confirmed by a positive troponin level. ST depression or T wave inversion may also indicate low oxygen supply in the heart suggesting a partial blockage or hypokalemia.

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Some patients may not have troponin elevations that becomes clinically significant that may still require further evaluation. Clinicians can run a stress test on these patients to ensure they are in a stable condition. One stress test method involves having their patients exercise by running on a treadmill while monitoring their EKG and chest pain. Upon changes to their ST wave or onset of chest pain the stress test should be discontinued to prevent a critical event. Another stress test that can be utilized involves injecting a nuclear dye marker into the arteries which can be visualized to assess for blockage. These dyes or contrast can be extremely toxic to the kidneys which can lead to acute kidney injury or chronic kidney disease.

Patients being injected with dye should be taken off any medications that can exacerbate kidney damage such as NSAIDs, and even metformin at least until the dye has been completely cleared. They should also be instructed to hold substances for 24-48 hours including caffeine (including decaffeinated beverages), cigarettes, medications that can affect coronary blood flow (nitroglycerin, betablockers, theophylline), and should not eat or drink for 4 hours before or after the intervention.

Patients should be encouraged to drink plenty of water after the procedure to dilute the dye. Patients with an allergy to iodine – where the allergy involves more than just facial flushing – should not be given contrast. Kidney function should be monitored with contrast use with a serum creatine – a Scr > 1.3 or a CrCL < 30 ml/hr serves as a potential contraindication to dye use.

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Treatment

Time to treatment is critical when treating patients who may be having a heart attack. The goal is to unclog their arteries as soon as possible to achieve optimal results and prevent serious cardiac damage. For this reason, troponin positive patients may be admitted to the catheterization lab to both identify the clot and treat it if present. Patients should not be eating for 6-12 hours prior to the admission to the cath lab.

A common surgical intervention is called a percutaneous coronary intervention or PCI. This procedure involves inserting a balloon into the coronary artery – inflating the balloon to dilate blood vessel and allow for blood flow – then inserting a cage to maintain the dilation and blood flow through the coronaries.

Another surgical intervention is called a coronary artery bypass grafting (CABG). This procedure involves extracting a blood vessel from another part of the body (usually the leg) and attaching it to a part of the heart before the blockage and another part after the block. This allows blood to flow normally in the heart by literally bypassing the block. A CABG is more invasive than a PCI which therefore extends recovery time – requiring more time in the hospital. A MIDCAB is a minimally invasive bypass which is a similar procedure that requires a smaller incision.

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After the cath lab patients should be advised to avoid heavy lifting and any situation where the incisions may become soaked. The goal is to prevent infection because if the tissue becomes infected it can lead to serious complications. After a cath procedure there it is important to note that if the pedal pulse cannot be palpated the healthcare provider should be notified, as well as remarkably cool legs which suggests very low perfusion. However, the pedal pulse should be diminished for 4-12 hours after the procedure but any longer requires referral.

Pharmacology of Myocardial Infarctions

Initially patients admitted for suspected or diagnosed MI will be treated with oxygen as well as medications that can improve blood flow. These steps should be made prior to catheterization procedures as the preparations are made for surgical or pharmacological interventions to remove the clot. Nitroglycerin or similar medications are used as a vasodilator to improve blood flow in the coronary arteries. They should also be provided morphine which can help with pain as well as reduce the stress to the heart. When morphine fails to relieve the patient of pain their condition may be assessed as critical. Lastly, these patients may be put on aspirin which reduces the formation of platelets – thus preventing the clot from getting worse.

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Under certain circumstances a patient may be eligible to receive thrombolytics which are used to dissolve and breakup the clot as an alternative to surgical intervention. These agents should only be used around 2-6 hours after the initial MI. Thrombolytics are extremely dangerous medications as they can cause massive bleeding throughout the body. For this reason, there are many contraindications to using thrombolytics including active internal bleeding, current intracranial hemorrhage, severe uncontrolled hypertension, and serious head trauma that occurred within the last three months.

There are two main thrombolytic agents that are used for myocardial infarctions. The more commonly used one is called TPA or alteplase. The other kind of thrombolytic used is streptokinase which is used less commonly due to higher prevalence of allergies including anaphylaxis.

After the clot has been treated in patients, they will likely be put on heparin via IV route which is a blood thinner. It is important to recognize that heparin acts to prevent clots from being form rather than breaking the clot up. Therefore, heparin should never be used to treat an MI as it plays a role mostly in prevention.

Patients should also be provided medications that can reduce the oxygen demands on the heart while improving blood flow. They may be initiated on nitroglycerin IV drip which will dilate the coronary arteries to improve perfusion. Patients may also be put on a beta blocker or a calcium channel blocker that works on the heart (verapamil, diltiazem). These agents act to reduce the frequency of hear beats as well the force of the contractions. This ultimately helps the heart by reducing the amount of oxygen and nutrients it needs and therefore reduces the stress to the cardiac tissue.

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After an MI a patient will be chronically put on a variety of medication to reduce their risk of having another heart attack. They will be put on an ACE inhibitor or ARB as well as other blood pressure medications that can help reduce cardiac damage and even encourage remodeling of the cardiac tissue such as spironolactone. They will also be prescribed antiplatelet medications. Patients will also be discharged with a prescription for sublingual nitroglycerin which can be used when symptoms of angina are present. These can be dissolved under the tongue and can be repeated every 5 minutes until symptomatic resolution. If symptoms do not improve after the first five minutes, they should call 911 to treat another potential MI. Other forms of nitrates may also be prescribed to be taken daily in post-MI patients. It is essential to note that if they are prescribed nitrates, they should never be prescribed sexual enhancement medications like sildenafil (Viagra) or tadalafil (Cialis) as they can cause a life-threatening drug interaction.

Nursing Interventions

Post MI patients will need to be provided with numerous consultations and monitored for a variety of complications. The first being the possibility of cardiogenic shock where a patient’s blood pressure becomes very low as a result of reduced cardiac output. Signs and symptoms for cardiogenic shock includes agitation, cool pale skin, and low urine output. These patients should be treated with vasodilators to increase blood pressure (e.g. norepinephrine, epinephrine and dopamine).

Post MI patients are also at increased risk of developing a dysrhythmia – critical forms include ventricular fibrillation or ventricular tachyarrhythmia. These dysrhythmias occurs in around 90% of recovering MI patients. Patients who do not have a pulse and are going through V Fib should be defibrillated (before performing CPR). Patients who have a pulse that can be counted can undergo cardioversion to correct the arrhythmia.

Another significant complication that can occur after an MI is heart failure which can become chronic. Patients with heart failure essentially have issues adequately pumping blood throughout their body – as a result fluid can start to buildup in the lungs and periphery of the patient. These patients should be instructed to weigh themselves everyday to monitor for increased fluid retention. In the event of serious edema in the lungs or periphery loop diuretics like furosemide or torsemide may be used to alleviate these symptoms. These patients should also have their heart sounds monitored for S3 heart sounds.

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Another complication that can occur is pericarditis which involves inflammation around the heart which can lead to deadly pericardial effusion causing the heart to stop bleeding. Signs and symptoms include jugular vein distension, extreme low blood pressure, and the inability to hear heart sounds. The last serious complication to monitor for is mitral valve prolapse where the valve becomes torn. These patients will have a heart murmur and may develop atrial fibrillation.

Several lifestyle recommendations should be provided to patients to prevent the onset and/or progression of heart failure. The goal is to reduce stress to the heart as much as possible which means they should be advised to take it easy for a few weeks after their MI. Additionally they should be instructed to restrict sodium to < 2 grams/day and fluids to < 2 liters/day. They should also be advised to reduce stress, alcohol consumption caffeine.

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Post MI patients should have a cholesterol panel taken and evaluated. Cholesterol goals includes a total cholesterol < 200, triglycerides < 150, LDL < 100, and HDL (good cholesterol) > 40. These patients should be instructed to avoid high cholesterol foods such as red meats and may be prescribed statins to reduce cholesterol levels. Statins may be prescribed for these patients to lower their LDL levels but should be used with caution in patients with liver disease. Additionally, they should be told to increase their fiber intake with fruits and vegetables.

Other important counseling points to be made includes increasing exercise (with caution) up to 30 minutes a day for 5 days/week. Patients who smoke should be advised to pursue smoking cessation treatment with their providers to prevent scarring and atherosclerotic risk. Finally, post MI patients will have to avoid sexual intercourse as this can increase the risk of a heart attack. They should only be allowed to have sex after they can climb 2 flights of stairs without shortness of breath.

Conclusion

Myocardial infarctions are very serious but unfortunately common events in the medical industry today. Medicine and surgery have come a long way in treating heart attacks as well as preventing future ones.

Nevertheless, the modern lifestyle appears to contribute heavily to the likelihood of having an MI which means the prevalence of myocardial infarctions will remain high. It is critical to understand the signs and symptoms as well as treatment modalities to save the lives of your patients – which is why it is important to understand this subject matter when preparing for the NCLEX™ exam.

References

  1. Heart Attack Facts & Statistics. Centers for Disease Control and Prevention. https://www.cdc.gov/heartdisease/heart_attack.htm. Accessed October 6, 2019