FRANKFURT, Germany (AP) — European Central Bank head Mario Draghi has called off his trip to an annual conference of central bankers in Jackson Hole, Wyoming, due to a heavy workload as top ECB officials shape their plans to intervene in bond markets and lower borrowing costs for indebted governments.

The bank holds a key meeting Sept. 6 where key aspects of any government bond purchases will be discussed.

An ECB spokesperson asked about the matter Tuesday said that Draghi decided not to go “because of the heavy workload foreseen in the next few days.”

Key questions remain about how the purchases would work, how big they might be, whether the ECB will target a particular bond yield level, and how the ECB’s holdings will be treated relative to other creditors.