NEW YORK--(BUSINESS WIRE)--Lower coupons, particularly in the US non-financial investment-grade space, are helping to propel bond issuance to record levels, according to Fitch Ratings. The outstanding high-grade par-weighted average coupon was 4.46% at July 31, down from 4.68% one year earlier. The overall outstanding par-weighted average coupon was 5.1%. The corporate bond universe totaled $3.9 trillion as of June 30, gaining 12% from the prior year and split 74%/26% between investment and spe