What are some things that cause bigeminy arrhythmia?

Many. Bigeminy means that every other beat arises prematurely causing a regularly irreglar rhythm in a cadence similar to 2 eighth notes followed by a rest and repeating. Electrolyte imbalance, caffeine, excess thyroid hormone, xs alcohol, decongestants, nicotine, stress, lack of sleep are typical. Ischemia and cardiomyopathy should be ruled out. Often no cause can be found. There are also rare causes.