What inotrope should be used in inferior wall myocardial infarction (MI) with suspected right ventricular infarction?

Inotrope Selection in Inferior Wall Myocardial Infarction with Right Ventricular Involvement

Dobutamine is the preferred inotrope for inferior wall myocardial infarction with right ventricular involvement, starting at 2.5-5 μg/kg/min and titrating up to 10-20 μg/kg/min as needed for hemodynamic instability not responsive to volume challenge. 1

Diagnosis of Right Ventricular Infarction

Before selecting an inotrope, it's critical to confirm right ventricular involvement in inferior MI:

• Obtain a right precordial lead (V4R) to detect ST-segment elevation ≥1mm, which is highly predictive of RV infarction 2, 1
• Perform echocardiography to assess for RV dilation and dysfunction 1
• Look for the classic triad (though only 25% sensitive) of hypotension, clear lung fields, and elevated jugular venous pressure 1

Treatment Algorithm for Inferior MI with RV Involvement

Step 1: Volume Optimization

• First optimize RV preload with IV normal saline boluses (target right atrial pressure ≥10 mmHg) 1
• Avoid nitrates, morphine, and diuretics as they reduce preload and can cause profound hypotension 1

Step 2: Inotropic Support (when hypotension persists despite adequate volume)

• First-line inotrope: Dobutamine

  • Start at 2.5-5 μg/kg/min and titrate up to 10-20 μg/kg/min 2, 1
  • Particularly effective for RV dysfunction as it improves RV contractility while reducing pulmonary vascular resistance 3
  • Studies show dobutamine significantly improves cardiac index and right ventricular ejection fraction in RV infarction 3

• Alternative inotropes:

  • Dopamine (5-20 μg/kg/min) if SBP 70-100 mmHg with signs/symptoms of shock 2
  • Consider low-dose dopamine (2.5-5.0 μg/kg/min) specifically for renal hypoperfusion 1

Step 3: For Refractory Shock

• Consider mechanical circulatory support (IABP or RV assist devices) 1
• Consider pulmonary artery catheterization to guide therapy in complex cases 1

Evidence Supporting Dobutamine in RV Infarction

Dobutamine is superior to other inotropes in RV infarction because:

1. It improves RV contractility while simultaneously reducing pulmonary vascular resistance, optimizing both RV function and LV preload 3

2. Comparative studies show dobutamine produces significantly greater improvements in cardiac index (2.0±0.4 to 2.7±0.5 L/min/m²) and right ventricular ejection fraction (30±8% to 42±7%) compared to vasodilators like nitroprusside 3

3. ACC/AHA guidelines specifically recommend dobutamine for hemodynamic instability in RV infarction not responsive to volume challenge 2, 1

Important Caveats and Pitfalls

• Volume status first: Inotropes should only be initiated after adequate volume resuscitation, as RV preload is critical 1

• Avoid vasodilators: Nitrates can cause profound hypotension in RV infarction by reducing preload 1

• Monitor for arrhythmias: Dobutamine can increase heart rate and trigger arrhythmias, requiring careful titration 4

• Temporary use only: FDA labeling indicates dobutamine is only for short-term use (typically <48 hours) 4

• Maintain AV synchrony: Correct bradycardia and heart blocks, as AV synchrony is crucial for optimal RV function 2, 1

• Consider reperfusion: Early reperfusion therapy remains the cornerstone of treatment for any MI with RV involvement 2, 1

By following this approach and selecting dobutamine as the preferred inotrope after optimizing volume status, you can effectively manage the hemodynamic compromise associated with inferior MI complicated by RV involvement.