What are the key components, assessment, and management of the cardiac system, including post-cardiac surgery care and Inferior STEMI (ST-Elevation Myocardial Infarction) in the Cardiovascular Intensive Care Unit (CVICU)?

Inferior STEMI in CVICU: Assessment, Management, and Critical Care Considerations

Anatomy and Pathophysiology of Cardiac System in STEMI

Inferior STEMI occurs when there is complete occlusion of the right coronary artery (RCA) or circumflex artery, leading to myocardial necrosis in the inferior wall of the left ventricle. 1, 2

• The cardiovascular system consists of the heart as the central pump and a network of blood vessels that distribute blood throughout the body, with coronary arteries supplying the myocardium itself 3
• Coronary thrombosis is the primary pathophysiologic mechanism in STEMI, involving both platelet aggregation (initiating mural thrombus) and fibrin formation (stabilizing the thrombus) 1
• In inferior STEMI, the right coronary artery (which supplies the inferior wall of the left ventricle) becomes occluded, leading to ischemia and eventual necrosis of cardiac tissue 1
• Approximately 25-30% of patients undergoing primary PCI for STEMI may have a patent infarct-related artery at initial angiography, suggesting spontaneous reperfusion 1

Clinical Presentation and Assessment of Inferior STEMI

Signs and Symptoms

• Chest pain/discomfort lasting 10-20 minutes or more that is not fully responsive to nitroglycerin 1
• Possible radiation of pain to the neck, lower jaw, or left arm 1
• In elderly patients, atypical presentations including fatigue, dyspnea, faintness, or syncope are common 1
• Evidence of autonomic nervous system activation including pallor, sweating, and hypotension or narrow pulse pressure 1

Key Components of CVICU Assessment

• Immediate 12-lead ECG showing ST-segment elevation of ≥1 mm in leads II, III, and aVF (inferior leads) 1
• Right precordial leads (V3R-V4R) should be obtained to assess for right ventricular involvement, which is common in inferior STEMI 1
• Assessment for reciprocal ST depression in leads I and aVL, which often accompanies inferior STEMI 4
• Cardiac biomarkers (troponin) to confirm myocardial necrosis 2
• Hemodynamic assessment for signs of right ventricular involvement (hypotension, elevated jugular venous pressure, clear lung fields) 1
• Echocardiography to assess wall motion abnormalities, right ventricular function, and potential mechanical complications 1

Management of Inferior STEMI in CVICU

Immediate Interventions

• Rapid triage and diagnosis with door-to-ECG time under 10 minutes 1
• Oxygen therapy if oxygen saturation is less than 90% 1
• Aspirin administration (162-325 mg chewed) 1
• Pain relief with intravenous morphine (2-4 mg) titrated as needed 1
• Nitroglycerin (sublingual or IV) if systolic blood pressure >100 mmHg and no right ventricular involvement 1
• Primary PCI is the preferred reperfusion strategy when it can be performed within 90 minutes of first medical contact 1
• If primary PCI cannot be performed within 120 minutes, fibrinolytic therapy should be administered within 30 minutes of hospital arrival 1

Special Considerations for Inferior STEMI

• Caution with nitrates in inferior STEMI with right ventricular involvement due to risk of profound hypotension 1
• Volume loading with normal saline (500-1000 mL) for patients with right ventricular involvement and hypotension 1
• Avoid beta-blockers in patients with signs of heart failure, risk for cardiogenic shock, or significant bradyarrhythmias 1
• Temporary pacing may be required for high-degree AV blocks, which are common in inferior STEMI 1

Reperfusion Strategies

• Primary PCI with door-to-balloon time ≤90 minutes is the gold standard 1
• For patients presenting to non-PCI capable facilities, rapid transfer for primary PCI is recommended if the first medical contact-to-device time can be achieved within 120 minutes 1
• If timely transfer is not possible, a pharmaco-invasive approach (fibrinolysis followed by transfer for angiography within 3-24 hours) should be considered 1
• Complete revascularization of non-culprit vessels during the index procedure may be considered in hemodynamically stable patients 1

Management of Complications in Inferior STEMI

Right Ventricular Infarction

• Present in up to 50% of inferior STEMIs and requires specific management 1
• Maintain right ventricular preload with IV fluid boluses (normal saline) 1
• Avoid nitrates, diuretics, and other preload-reducing agents 1
• Consider inotropic support with dobutamine if hypotension persists despite adequate fluid resuscitation 1

Bradyarrhythmias and Heart Blocks

• First-degree AV block and Mobitz type I (Wenckebach) second-degree AV block typically do not require treatment 1
• High-degree AV blocks (Mobitz type II or complete heart block) may require temporary transvenous pacing 1
• Atropine (0.5-1.0 mg IV) can be used for symptomatic bradycardia 1

Mechanical Complications

• Assess for papillary muscle rupture (acute mitral regurgitation), ventricular septal rupture, or free wall rupture 1
• New cardiac murmurs warrant immediate echocardiographic evaluation 1
• Surgical repair is indicated for most mechanical complications, with IABP support as a bridge to surgery 1

Cardiogenic Shock

• Occurs in approximately 5-8% of inferior STEMI patients 1
• Early invasive hemodynamic monitoring with pulmonary artery catheterization is recommended 2
• Inotropic support with dobutamine (2-20 μg/kg/min) for SBP 70-100 mmHg 1
• Vasopressor support with dopamine (5-15 μg/kg/min) or norepinephrine for refractory hypotension 1
• Consider mechanical circulatory support (IABP, Impella, ECMO) for refractory shock 2

Post-STEMI Care in CVICU

Monitoring and Assessment

• Continuous ECG monitoring for at least 24 hours or until alternative diagnosis is made 1
• Monitoring for ST-segment resolution provides important prognostic information 1
• Invasive arterial pressure monitoring for patients with cardiogenic shock 1
• Pulmonary artery catheterization for patients with low cardiac output, progressive heart failure, or suspected mechanical complications 1

Pharmacological Management

• Dual antiplatelet therapy with aspirin and a P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) 1
• Beta-blockers within 24 hours if no contraindications 1
• ACE inhibitors within 24 hours, particularly for patients with anterior infarctions or reduced ejection fraction 1
• Statin therapy (high-intensity) 1
• Aldosterone antagonists for patients with EF <40% and either heart failure or diabetes 1

Transition of Care

• Patients with uncomplicated inferior STEMI can be transferred from CCU to step-down unit after 12-24 hours of clinical stability 1
• Most uncomplicated STEMI patients can be discharged after 4-5 days 1
• Cardiac rehabilitation should be initiated prior to discharge 2

CVICU Tips for Inferior STEMI Management

• Obtain right-sided ECG leads (V3R-V4R) in all inferior STEMIs to assess for right ventricular involvement 1
• Maintain high clinical suspicion for mechanical complications, especially with persistent hemodynamic instability 1
• In patients with inferior STEMI and hypotension, administer fluid challenge before assuming cardiogenic shock, as right ventricular infarction often responds to volume loading 1
• Monitor for bradyarrhythmias and high-degree heart blocks which are more common in inferior than anterior STEMIs 1
• Consider early transfer to a tertiary care center for patients with cardiogenic shock or mechanical complications 1
• For patients requiring intubation, avoid excessive positive end-expiratory pressure which can worsen right ventricular function in RV infarction 2
• Implement a structured STEMI protocol with clear roles and responsibilities to minimize door-to-balloon time 1
• Use intracoronary imaging (IVUS, OCT) during PCI to optimize stent selection and deployment 2
• Consider complete revascularization during index hospitalization rather than staged procedures to reduce costs and improve outcomes 1