Prudential chairman Harvey McGrath did an admirable job defending Tidjane Thiam at this week's lively AGM, but the under-fire CEO will find it difficult to dodge the dagger-wielding institutions due to pitch up at his Paddington HQ in the weeks ahead.It's reported that Fidelity, Legal & General Investment Management and Schroders will demand a boardroom shake-up when they sit down with the life insurer's directors next week.There's little indication that the anger over the Pru board's failure to do a deal with AIA at the right price is fading. Shareholders were furious when they cross-examined directors at the QEII Conference Centre on Monday.Now, it's the heavyweight's turn. Richard Buxton, head of UK equities at Schroders, has aired his concerns about the Pru's leadership, which racked up costs of £450m during the disastrous attempt to buy AIA for $35.5bn then $30.4bn.The National Association of Pension Funds, which speaks for around 12% of the London stock market, is meeting management on 22 June to talk about the need for fresh faces at the top.Thiam's departure would clear the way for a return of former chief executive Mark Tucker, although Michael McLintock, chief executive of M&G, the Pru's asset management arm, is said to be amore likely candidate for the interim post.