ST Segment Elevation Acute Myocardial Infarction - Case Study

A 62-year-old man with a history of hypertension is mowing his law n at 9:00 a.m. on a Saturday morning when he experiences a heavy sensation in his chest. He stops mowing the lawn and within 10 minutes his symptoms resolve, and he resumes cutting the grass. Approximately 10 minutes later, he experiences severe, crushing chest pain associated with shortness of breath and pain radiating down his left arm. As he walks to his house, he becomes diaphoretic and nauseated, and vomits twice. At this point, he calls an ambulance and is taken to the ER. When you arrive to examine him, he is still experiencing severe pain. A 12-lead ECG reveals 3-mm ST-segment elevation in leads V2, V3, V4, and V5 w ith inferior ST-segment depression. The pain has been present for a total of approximately 45 minutes.

\1. What initial actions should be taken in this patient?
2. Is this patient's hypertension a contraindication to thrombolytic therapy?
3. What are the risks associated w ith thrombolytic therapy and how long after the onset of acute MI is therapy beneficial?
4. Which is the better reperfusion therapy for acute MI—thrombolytic therapy or primary percutaneous transluminal coronary angioplasty (PTCA)?
5. What therapies should be administered acutely w ith thrombolysis or primary PTCA?
6. What measures should be carried out before this patient is discharged?
7. Under w hat circumstances should the patients undergo coronary angiography if they did not undergo acute angioplasty and/or stenting on admission?


Case Discussion

1. What initial actions should be taken in this patient?
The first actions that should be taken in this patient are to administer sublingual NTG, administer oxygen if oxygen saturation is below 90%, and establish venous access. IV β-blockers and aspirin should be given. Analgesics such as morphine should be given if the pain does not resolve with NTG. Immediate transfer to the cardiac catheterization laboratory for coronary angioplasty and reperfusion
of the infarct-related artery is the treatment of choice if it can be accomplished within 3 hours of the onset of chest pain. If not, thrombolytic agents should be administered immediately if there are no contraindications. Patients should be questioned about contraindications to thrombolytic agents before administration.
Invasive procedures such as arterial puncture should be minimized if thrombolytic agents are to be administered to avoid bleeding. If the patient presents more than 3 hours following the onset of chest pain PCI is clearly preferable, because of the difficulty in lysing the clot after 3 hours. How ever, studies have show n that either thrombolytics or PCI is beneficial for at least 12 hours after the onset of pain.

2. Is this patient's hypertension a contraindication to thrombolytic therapy?
Hypertension alone is not a contraindication to thrombolytic therapy. If the hypertension is uncontrolled and cannot be lowered quickly to a level below 180/110 mm Hg, the risk of intracranial bleeding is increased. These thrombolytic agents can still be considered in individual patients.

Absolute contraindications to thrombolytic therapy include:

•  any prior intracranial hemorrhage (ICH), 
•  known cerebrovascular or intracranial neoplastic lesion,
•  ischemic stroke within 3 months, 
•  active bleeding excluding menses,
•  suspected aortic dissection, and 
•  significant closed head or facial trauma within 3 months. 

Relative contraindications in addition to uncontrolled hypertension are:

•  an old history of stroke, 
•  prolonged cardiopulmonary resuscitation (CPR) (more than 10 minutes) or 
•  major surgery within 3 weeks,
•  internal bleeding in the last 4 weeks,  
•  active peptic ulcer, 
•  a known bleeding diathesis or use of anticoagulants, and 
•  pregnancy.

3. What are the risks associated with thrombolytic therapy and how long after the onset of acute MI is therapy beneficial?
The major risk of thrombolytic therapy is bleeding. This risk is lowest with streptokinase, and highest with newer agents and when heparin is added to therapy. With alteplase-like agents, major bleeding occurs in approximately 5% of patients and ICH occurs in 0.9%. Factors that increase ICH include
age (especially greater than 75 years), weight less than 70 kg, and hypertension (160/95 or higher) at presentation and the use of alteplase. Patients w ith more than three risk factors have two or three times higher risk of ICH. Patients w ith acute MI benefit from thrombolytics for up to 12 hours after the onset of the infarction with earlier treatment leading to higher survival.

4. Which is the better reperfusion therapy for acute MI—thrombolytic therapy or primary PTCA?
PTCA is generally preferred over thrombolytic agents as a reperfusion therapy. Thrombolytics can be used in patients presenting early (<3 hours) especially when a catheterization laboratory is not readily available. Primary PTCA is preferred in most instances w here there is rapid access to a skilled
laboratory, especially in higher risk patients either due to cardiogenic shock or significant HF. It is also preferred in patients presenting later than 3 hours from symptom onset, w hen there are significant contraindications to thrombolytics or when the diagnosis is in doubt.

5. What therapies should be administered acutely with thrombolysis or primary PTCA?
Chewable aspirin (162.5 mg) should be administered immediately once the diagnosis is made in all patients unless there is a contraindication to aspirin (i.e., aspirin allergy or active bleeding). IV β-blockade should be instituted unless there are contraindications to their use such as pulmonary edema, significant atrioventricular block, heart rate less than 60 per minute, systolic blood pressure less than 100 mm Hg or significant bronchospasm and history of asthma. ACE inhibitors (or ARBs for allergic patients) should be begun within the first 24 hours in the absence of contraindications such as systolic blood pressure less than 100 mm Hg, renal insufficiency (serum creatinine greater than 3.0 mg/dL), or hyperkalemia. Clopidogrel should also be used during the hospital stay.

6. What measures should be carried out before this patient is discharged?
Therapy w ith a statin should be started. LDL cholesterol levels fall after the first 24 hours after an acute MI, so lipid level measurements should be done within 24 hours of admission. Risk stratification with submaximal exercise test and assessment of left ventricular EF should be performed in patients who were not stratified by angiography. If a stent w as placed during PTCA, clopidogrel is added for 3 to 6 months and perhaps longer if a drug-eluting stent was placed. Finally, an aldosterone antagonist should be added for patients with abnormal cardiac function and HF or diabetes. All patients should be counseled on smoking cessation and a low -fat diet. Each patient should be taught how to use NTG and should be instructed when to call for problems.

7. Under what circumstances should patients undergo coronary angiography if they did not undergo acute angioplasty and/or stenting on admission?
Residual ischemic myocardium and low EF are major risk factors for mortality. This is why patients with recurrent ischemic chest pain, a positive submaximal exercise test, or an EF less than 40% usually undergo coronary angiography to determine if residual lesions causing ischemia can be
corrected.