American executives are most optimistic about the prospects of economic growth over the next three years, drawing a stark contrast with corporate chieftains in 10 other countries, according to KPMG’s survey.A poll of 1,300 chief executives in 11 of the world’s largest economies showed that 87 per cent of US executives were either “confident” or “very confident” about the prospects of economic growth in the next three years, an improvement from 52 per cent last year.The rising confidence of…