Cocaine significantly impairs myocardial relaxation

Area of Science:

• Cardiovascular Physiology
• Pharmacology
• Toxicology

Background:

• Recreational cocaine use can lead to serious cardiovascular complications.
• Understanding cocaine's direct effects on cardiac function is crucial for managing toxicity.
• Propranolol is sometimes used to mitigate cocaine's cardiovascular effects, but its efficacy requires further study.

Purpose of the Study:

• To investigate the immediate impact of recreational doses of intravenous cocaine on myocardial ventricular relaxation and contraction.
• To assess cocaine's effects on coronary blood flow.
• To determine how propranolol administration modifies cocaine's cardiac effects.

Main Methods:

• A prospective study was conducted on twenty mongrel dogs.
• Hemodynamic parameters including central aortic pressure, left atrial and ventricular pressures, and coronary artery blood flow were continuously monitored.
• Electrocardiograms were recorded, and indices of ventricular contraction (dP/dt max) and relaxation (time constant of isovolumic ventricular relaxation) were calculated.

Main Results:

• Cocaine administration (2.5 and 5 mg/kg) significantly increased the time constant of isovolumic ventricular relaxation, indicating impaired relaxation.
• Higher doses of cocaine (5 mg/kg) also reduced the maximum rate of left ventricular pressure increase (dP/dt max) and decreased heart rate and coronary blood flow.
• Cocaine induced significant ST segment displacement on electrocardiograms, and co-administration with propranolol intensified the depressant effect on ventricular relaxation.

Conclusions:

• Intravenous cocaine substantially impairs myocardial ventricular relaxation for at least 40 minutes.
• Propranolol significantly intensifies cocaine's negative effect on ventricular relaxation.
• These findings highlight the detrimental impact of cocaine on cardiac function and the complex interaction with beta-blockers.