What additional measures to cardioversion may be necessary to prevent death and complications from cardiovascular causes?

Correct risk factors. Cardioversion is to correct a heart rhythm problem. To prevent heart attack and death you need to deal with your risk factors. Some of these are smoking, diabetes, high blood pressure, overweight, stress, lack of exercise, and a high cholesterol. Treatment of those conditions with medication or modifying your life style can reduce the risk of heart attacks and strokes.
Airways. I'm not sure if i understood your question correctly. If you're talking about someone who has cardiac arrest beside cardioversion and protection of airways restoration of hemodynamic is necessary to improve the patient's survival. Most important factor here is the downtime from cardiac arrest. Cooling process is another way to improve the outcome.