My version:
All attacks with a garrotte are at disadvantage. It deals d6 + strength damage on a hit and if you hit, the target is grappled and must make a Constitution saving throw with a DC equal to 8 + our proficiency bonus plus your strength modifier. If the creature failed the saving throw, the duration it can hold its breath is halved (minimum 30 seconds) - see below.
Until the grapple is broken, the target takes d6+ strength damage at the start of each of its turns. If you take an action, bonus action or reaction while the target is grappled, the grapple ends.
While the creature is grappled, it must hold its breath. A creature can hold its breath for a number of minutes equal to 1 + its Constitution modifier (minimum of 30 seconds). When a creature runs out of breath or is choking, it begins to suffocate and can survive for a number of rounds equal to its Constitution modifier (minimum of 1 round). At the start of its next turn, it drops to 0 hit points and is dying, and it can't regain hit points or be stabilized until it can breathe again. For example, a creature with a Constitution of 14 can hold its breath for 3 minutes, or 90 seconds if it failed the saving throw. If it starts suffocating, it has 2 rounds to reach air before it drops to 0 hit points.