It looks like you might benefit from some longer intervals. I believe 3 minutes is about the minimum required to reach vo2 max. Intervals of 3 to 8 minutes withh 20 to 30 minutes of total work time with equal recovery intervals (or less depending on fitness) is a good way to work vo2 max:
10 min warm-up
5x4 min hard, 4 min easy
10 min cool-down
10 to 30 minute intervals with 30 to 40 min total work time is a good way to target threshold:
10 min warm-up
20 minutes on
5 min easy
20 min on
5 min cool down
The only problem is trying to gauge the intensity of your intervals by heart rate. Obviously the shorter intervals are done at a higher intensity than the longer ones. It should feel like you're going as hard as you can go for the duration of the interval, while maintaining a constant cadence and gear. This makes for a constant effort or power output. Have you done any self-testing to set heart rate zones?
The 20 minute intervals should be done at 95 to 105% of the highest heart rate you can maintain for 1 hour. The 4 minute intervals should be done at 106% to ~110% of the highest heart rate you can maintain for 1 hour. The interval starts when you start going hard, not when your heart rate reaches the target. You may have to employ trial and error to get the gearing and cadence right. Hope this helps.