Module 7.1 - Myocardial Infarction

Question 1

What are the 3 presentations of ACS?

Answer 1

1. Unstable angina
2. Acute non-ST elevation myocardial infarction (NSTEMI)
3. Acute ST-elevation myocardial infarction (STEMI)

Resting angina, new onset angina that markedly limits physical activity and angina increasing in duration, frequency and with less exertion suggest ACS

Question 2

What is unstable angina?

Answer 2

If the coronary flow is not severe enough or the occlusion in the artery is not severe enough to cause myocardial necrosis and a subsequent positive biomarker reading, the syndrome is classified as UA.

Question 3

What is a NSTEMI?

Answer 3

• Defined as the elevation of cardiac biomarkers and the absence of ST segment elevation on the ECG.
• Like STEMI can lead to cardiogenic shock.
• The short term occurrence of morbidity and mortality is less than STEMI.
• Long term occurrence is the same.

Question 4

What is a STEMI?

Answer 4

• Defined as a clinical syndrome of myocardial ischemia in association with persistent 12 lead ECG changes of ST segment elevation (injury pattern) causing necrosis and elevation of biomarkers.
• Compared to UA/NSTEMI there is a higher in hospital and 30 day morbidity and mortality.
• Can lead to arrhythmias, cardiogenic shock, and heart failure.
• Accounts for 20-30% of ACS cases annually.

Question 5

What cardiac enzymes are evaluated with ACS?

Answer 5

• Troponin is myocardial specific and is the preferred biomarker for ACS with troponin I rising slightly faster than troponin T (3 hrs. vs. 6 hrs.)
  
  • If the first troponin is negative, a second measurement should be drawn 6-8 hrs later before a final diagnosis is made.
• Other biomarkers include creatine kinase isoenzyme MB (CK-MB) and myoglobin with myoglobin rising within 1-2 hours and CK-MB rising 4-12 hours.
• CK-MB is an acceptable cardiac marker but lacks the specificity as it is also present in both skeletal and cardiac muscles.
• A CK-MB/total CK fraction would delineate cardiac muscle damage. A positive result is > 5% as this suggests injury.
• Because of the variability of the enzymes rising, serial enzyme testing (troponin) is needed every 6-8 hours regardless of the resolution of symptoms.

Question 6

Describe the inpatient management of a patient with ACS

Answer 6

1. Admit to coronary care unit (CCU) for observation and to rule out NSTEMI and STEMI
2. Begin beta-blocker therapy

• Give initial dose of metoprolol 25-50mb PO BID within 24 hours.
• The target dose is 50-100mg PO BID.
• If the dose needs to be stopped taper dose over 1-2 weeks, DON’T ABRUPTLY DISCONTINUE

3. Morphine 2-4mg IV

• Used as an adjunct to beta blockers, nitrates and calcium channel blockers
• Use of morphine alleviates the negative responses that occur when the sympathetic nervous is activated by pain; such as: diaphoresis, weakness, lightheadedness and palpitations that increase the cardiac workload and oxygen demand.

4. Heparin

• Heparin IV. 60u/kg IV bolus followed by 12u/kg/hr with a goal of PTT between x1.5-2 normal. Higher risk of HIT
• Heparin Sub-q. Low molecular weight heparin (enoxaparin, Lovenox) is an alternative for ACS or NSTEMI. Start @ 1mg/kg Sub-q BID. Lower risk of HIT. If Cr > 2.0 or GFR <30mL/min reduce dose by 50%.

5. Persistent Angina despite the above interventions + Nitroglycerin sublingual?

• Start Nitroglycerin IV @ 5-10mcg/min
• May increase dose by 5-10 mcg/min q 5min until the angina is relieved or the patient develops hypotension (SBP < 90mmHg)

6. Consider Risks
   * If pt has STEMI, consider fibrinolytic/thrombolytic therapy
   * Assess pt for cardiac catheterization and possible percutaneous transluminal coronary angioplasty (PTCA) or coronary bypass graft (CABG) surgery

Question 7

How is the Thrombolysis in Myocardial Infarction (TIMI) risk score used?

Answer 7

• It is used to determine the risk of death or nonfatal MI up to 1 year after an ACS event. Patients can be classified as low, intermediate or high risk based on their clinical profile.
• Patients with a TIMI risk of 0 and negative troponins have a very low 30 day rate of major adverse cardiac events.
• Patients with a TIMI risk score of > 3 benefit from aggressive medical therapy and invasive evaluation.

Question 8

What adjunct medical therapy is started for patients with UA/STEMI?

Answer 8

This therapy may be started immediately on admission or as part of the discharge process

1. PPIs - Started in pts that require antiplatelet therapy and where the risk of GI bleeding is high/known ulcers
2. ACE Inhibitors - Used to control HTN and should be started if the LV function is compromised. Calcium channel blockers should be avoided because of increased morbidity and mortality in acute STEMI patients.
3. Aldosterone antagonists - Start after ACE initiation if pt has diabetes or LVEF <40%
4. Statin Therapy - Reduces the risk of recurrent ischemia, MI and death in patients with CAD. Goal LDL is < 70 mg/dL.
5. Diabetes control - Goal is a blood sugar < 180 mg/dL while avoiding hypoglycemia. Avoid controlling BG too tightly in ACS because it may increase mortality

Question 9

What is Fibrinolytic/Thrombolytic Therapy?

Answer 9

Pharmacological process where agents are used to restore blood flow to the myocardial by lysing clots within the coronary arteries. Approximately 90% of NSTEMI involve a thrombus

Question 10

What are the indications for fibrinolytic/thrombolytic therapy?

Answer 10

• If a PCI is not available within 90 minutes of the ischemic event, this is the preferred treatment for STEMI
• Unrelieved chest pain that has been present longer than 30 minutes but less than 6 hours. Some hospitals will administer up to 24 hours.

Question 11

How is a reperfusion therapy (fibrinolysis or invasive) chosen for ST-segment elevation or new LBBB?

Answer 11

If pt. presentation is less than 3 hrs and no delay for PCI, then there is no preference for either strategy

Question 12

If a patient presents with a ST segment elevation or new or presumably new LBBB and it has been < 3 hrs and no delay for PCI, when is fibrinolysis preferred over PCI?

Answer 12

• Early presentation (3 hrs or less from onset of symptoms)
• Invasive strategy is not an option or would be delayed (No access to PCI suite, difficult vascular access)
• Medical contact-to-balloon or door-to-balloon is longer than 90 minutes
• (Door to balloon) minus (door to needle) is longer than 60 minutes
• No contraindication to fibrinolysis

Question 13

If a patient presents with a ST segment elevation or new or presumably new LBBB and it has been < 3 hrs and no delay for PCI, when is PCI is preferred over fibrinolysis?

Answer 13

• Late presentation (symptom onset longer than 3 hours prior)
• Skilled PCI facility available with surgical back up
• Medical contact-to-balloon or door-balloon is less than 90 minutes
• (Door-to-balloon) minus (door-to-needle) is less than 60 minutes
• Contraindications to fibrinolysis including an increased risk of bleeding and intracranial hemorrhage; high risk from STEMI (CHF, Killip class > 3); diagnosis of STEMI is in doubt

Question 14

What is Percutaneous transluminal coronary angioplasty (PTCA)/Percutaneous coronary intervention (PCI)?

Answer 14

It is an invasive procedure that involves a narrow catheter with an inflatable balloon tip that is inserted percutaneously and threaded into the coronary arteries under fluoroscopy. The balloon is temporarily inflated which serves to compress the atherosclerotic plaque against the arterial walls resulting in dilatation of the lumen of the affected coronary artery. A stent is then inserted into this opening to keep the artery open.

Question 15

What are the 2 types of stents used for PTCA/PCI?

Answer 15

1. Bare metal stents are typically used for patients who are at high risk for bleeding or who may require surgical procedures within the next 12 months or who are unlikely to remain compliant with the anticoagulation therapy that is required for 12 months
2. Drug eluting stents (DES) require 12 months of dual antiplatelet therapy consisting of aspirin and Clopidogrel (Plavix) which is generally the drug of choice to be given with aspirin as dual antiplatelet therapy

Question 16

How is Clopidogrel (Plavix) used for PCI?

Answer 16

• Clopidogrel (Plavix) inhibits platelet aggregation. It reduces cardiovascular mortality and recurrent MI, both acutely and at 11 months.
• A loading dose should be given pre PCI for naïve patients. If patients cannot take PO pre-procedure, rectal administration is unproven but has been reported

Question 17

How is Asprin used for PCI?

Answer 17

Post PCI the aspirin dose is 81 mg daily when given with Plavix

Question 18

What are the indications for using PCI?

Answer 18

• PTCA is the preferred mode of treatment for MI only when it is immediately available to patients (less than 90 minutes from arriving at the ED [door}.
• It is indicated when there are EKG changes that may include ST segment depression or elevation, or onset of left bundle branch block (LBBB)
• When there is an evolving MI
• When angina (recent onset or if the condition is stable but does not respond to medical therapy)
• When there is adequate ventricular function and collateral circulation
• For relatively proximal and non-calcified lesions
• When the lesions are not involving a major bifurcation

Question 19

What are some potential complications post-PCI?

Answer 19

• Post procedure the patient will need to be observed for signs of reperfusion that may include EKG changes, relief from angina
• Restenosis may occur in 30-40% of patients. Patients will exhibit ACS symptoms with angina, ST segment elevation and/or arrhythmias. They may need an emergency repeat PCI or bypass surgery.
• Contrast dye allergy – observe for signs of anaphylaxis
• Hematoma formation at the site of catheter insertion (groin)
• Coronary artery perforation, embolism, spasm or MI

Question 20

What is a Coronary Artery Bypass Graft (CABG)?

Answer 20

Surgical procedure in which the affected areas of the heart that are ischemic are revascularized through a grafting approach from the aortic root to a point distal to the ischemic lesion, using either the internal mammary artery (best for long term patency), saphenous vein, radial artery or gastroepiploic artery

Question 21

What are the indications for a Coronary Artery Bypass Graft (CABG)?

Answer 21

• Refractory unstable angina (UA)
• MI
• Failed PCI
• Greater than 50% left main artery occlusion
• Triple vessel coronary artery disease
• Left ventricular failure related to heart failure or cardiogenic shock

Question 22

How do you manage a CABG patient in the intermediate postoperative period?

Answer 22

1. Monitor for arrhythmias

• Afib occurs in 20-30% of these pts. If it persists longer than 24 hours pt. will require anticoagulation to prevent stroke.
• Amiodarone gtt for atrial fibrillation
• Esmolol – a beta blocker for tachycardia and afterload reduction
• Diltiazem – calcium channel blocker for tachycardia

2. Monitor hemodynamics

• PA Catheter
• Arterial Line - BP monitoring
• Epicardial pacing wires - in place for potential bradycardia

3. Vasopressors

• Blood pressure support – Dopamine; Norepinephrine for severe shock
• Increase cardiac output – inotropes such as Dobutamine or Milrinone
• Treat transient hypertension – Nitroprusside
• Coronary and systemic vasodilation to decrease preload and myocardial oxygen consumption – Nitroglycerin

4. Mechanical Ventilation
   * The pt. will be intubated for a short period, attempt extubation within a 2-6hr period in most pts.
5. Monitor electrolytes
   * Goal range of serum potassium is 4.5-5.0 mEq/L and serum magnesium of 2.0
6. Chest tubes
   * Mediastinal chest tubes x 2 are the usual. They will be watched closely for evidence of bleedings. As a general rule if the output exceeds 400 ml within 2 consecutive hours or 300-500 ml in an hour, re-exploratory surgery is indicated
7. Monitor for Stroke

Question 23

What is a cardiac tamponade?

Answer 23

An accumulation of blood and/or fluid in the pericardial space. This can be a life threatening complication from an MI, PCI or bypass surgery that results in a decrease in cardiac output.

Question 24

What are the physical exam findings associated with cardiac tamponade?

Answer 24

• Beck’s triad – JVD, narrowing pulse pressure, distant heart sounds
• Tachycardia, hypotension, signs of shock
• Pulsus paradoxus - > 10 mm Hg
• Change in level of consciousness, especially if the patient appears anxious or confused
• Oliguria
• Other signs of circulatory shock

Question 25

What are the laboratory/diagnostic tests associated with cardiac tamponade?

Answer 25

• Echocardiogram, transthoracic (TTE) is used to confirm diagnosis. Features suggestive of tamponade are a dilated incompressible IVC, significant respiratory variation of tricuspid and mitral inflow velocities, early diastolic collapse of the RV and systolic collapse of the RA. A circumferential effusion may be seen.
• Echocardiogram, trans esophageal (TEE) may be needed if the TTE is of poor quality or if there is suspicion of loculated effusions. This is a particular post CABG concern.
• EKG – low voltage is likely with larger effusions. You will also see tachycardia and electrical alterations
• Chest x-ray may show widening mediastinum

Question 26

How do you manage a patient with a cardiac tamponade?

Answer 26

• The role for medical therapy is limited due to the urgency of the finding
• The filling pressures of the heart must be maintained with IV fluids and diuretics avoided. All medications that affect blood pressure should be held even those to control heart rate. The tachycardia compensates for a decreased cardiac output.
• Surgical management might be needed. An open pericardiocentesis with creation of a pericardial window is an option to prevent further effusions. It also allows for pericardial biopsies to be taken to assist in diagnosis

Question 27

What are the implications for the geriatric population that have had an MI?

Answer 27

• Individuals older than 75 years do better with a PCI than thrombolytic therapy
• The risk of hemorrhagic stroke increases in patients older than 85 years