What is Diltiazem's effect on cardiac index?

Diltiazem's Effect on Cardiac Index

Diltiazem increases cardiac index by approximately 20% in patients with heart failure through a combination of afterload reduction, heart rate reduction, and preserved contractility. 1

Mechanism of Action and Hemodynamic Effects

• Diltiazem is a non-dihydropyridine calcium channel blocker that inhibits calcium influx during membrane depolarization of cardiac and vascular smooth muscle 2
• It causes coronary vasodilation and peripheral vasodilation, resulting in decreased systemic vascular resistance 2
• Unlike some other calcium channel blockers, diltiazem has minimal negative inotropic effects in most clinical scenarios 2

Cardiac Index Effects in Different Patient Populations

Patients with Heart Failure

• In patients with advanced heart failure (NYHA class III-IV), intravenous diltiazem has been shown to increase cardiac index by 20% (from 2.05 to 2.47 L/min/m²) 1
• This improvement occurs alongside a 50% increase in stroke volume index and 27% increase in stroke work index 1
• The cardiac index improvement is achieved through:
  • 23% reduction in heart rate
  • 18% reduction in mean arterial pressure
  • 34% reduction in pulmonary wedge pressure
  • Without significant alteration in maximal first derivative of left ventricular pressure (dP/dt max) 1

Patients with Left Ventricular Dysfunction

• In patients with coronary artery disease and left ventricular dysfunction (EF <40%), intravenous diltiazem (0.5 mg/kg) preserves cardiac index while reducing heart rate and systemic vascular resistance 3
• End-systolic volume decreases, leading to increased stroke volume and ejection fraction 3

Perioperative Cardiac Surgery Patients

• In cardiac surgery patients, particularly those with left ventricular hypertrophy, diltiazem improves postoperative cardiac performance with higher cardiac output and cardiac index compared to control groups 4

Clinical Considerations and Precautions

• Contraindications and Precautions:

  • Avoid in patients with AV block greater than first degree or SA node dysfunction (without pacemaker) 5
  • Use with caution in patients with decompensated systolic heart failure or LV dysfunction 5
  • Avoid in patients with cardiogenic shock 5
  • Use cautiously in patients with WPW syndrome with atrial fibrillation/flutter 5

• Potential Adverse Effects:

  • Hypotension is a common side effect that may limit dosing 5, 2
  • Bradycardia may occur, particularly when combined with beta blockers 2
  • Transient junctional arrhythmias have been observed in some patients 1
  • Abnormal liver function tests and acute hepatic injury (rare) 5

Dosing Considerations

• Intravenous Administration:

  • Initial dose: 0.25 mg/kg IV bolus over 2 minutes 5
  • Maintenance infusion: 5-10 mg/h, up to 15 mg/h 5
  • For heart failure studies: 100-200 μg/kg/min infusion has been used 1

• Oral Administration:

  • Immediate release: 30-90 mg four times daily 5
  • Slow release: 120-360 mg once daily 5

Comparison to Other Calcium Channel Blockers

• Unlike dihydropyridines (e.g., nifedipine), diltiazem has less pronounced peripheral arterial vasodilation 5
• Compared to verapamil, diltiazem has less myocardial depression and is better tolerated in patients with mild to moderate left ventricular dysfunction 5
• Heart rate-slowing calcium channel blockers like diltiazem are preferred over dihydropyridines when beta blockers cannot be used 5

In conclusion, diltiazem generally has a favorable effect on cardiac index, particularly in patients with heart failure, through its balanced effects on heart rate, afterload reduction, and preserved contractility. However, careful monitoring is required, especially in patients with conduction disorders or severe left ventricular dysfunction.