A garrotte is a chord used to strangle people - so, if the attacker makes a successful attack, they have the chord around the target’s neck. Thereafter, each round following, the target suffers 1D6 damage + damage bonus.
On the first round - the attacker makes an Fighting (Garrote) roll - the target chooses to fight back (Brawl or Fighting Maneuver) or to Dodge - the outcome determined like for any combat, except if the attacker wins, they are strangling the target with the garrotte.
Each round following, the target may try to escape on their DEX turn - they must make a Fighting Manoeuvre roll - (their Fighting (Brawl) roll versus the attacker’s Fighting (Garrote) in an opposed roll). If the target wins, they break free from being strangled. If the attacker wins, the target is held and continues to be strangled - suffering 1D6+DB damage that round. If the target does not break free, eventually the 1D6 damage per round will kill them.