The effect of turning off a lead depends on which lead it is and what function it was providing. ICDs can have between one and three leads, each connected to a different chamber of the heart or serving a different purpose.
A lead may be turned off because it is no longer functioning correctly, because it is causing inappropriate sensing or therapy, or because a new lead has been added to replace its function. In some cases a lead is left in place but deactivated rather than removed, as lead extraction carries its own risks.
Whether the device can still deliver full therapy after a lead is turned off depends on the configuration. If the defibrillation lead is unaffected, the device can still deliver a shock when needed. If a pacing lead is turned off, the device may pace less effectively or not at all in certain situations. Your cardiologist will explain exactly what the change means for your individual device programming and what, if any, additional monitoring or precautions are needed.
If a lead has been turned off and you are unsure what that means for your protection, ask your ICD clinic directly. You are entitled to a clear explanation of how your device is currently configured and what it will and will not do.