In this letter, we present a novel approach to deriving triggering rules for event-triggered control (ETC) based on integral quadratic constraints (IQCs). The closed-loop system is considered as a feedback interconnection of two subsystems: one describes the behavior of the system state and the other the sampling-induced error. An IQC for the sampling-induced error is used as the ETC triggering rule. Transmissions are triggered if this IQC would otherwise be violated. We provide a method to synthesize the multiplier for the IQC based on linear matrix inequalities, such that asymptotic stability and a lower bound on the inter-event times are guaranteed. Moreover, the proposed approach allows for the incorporation of additional performance criteria to ensure further properties of the closed-loop system, such as a bound on the ${{\mathcal {L}}}_{2}$ -gain.