Atrial Trigeminy

A repeating pattern where every third beat is a premature atrial contraction. Two normal sinus beats are followed by one PAC, then the cycle repeats. Less ectopic burden than bigeminy.

• Repeating groups of three: two normal sinus beats followed by one PAC with abnormal P-wave morphology.
• The pattern is highly regular.
• Narrow QRS on all beats.

Less hemodynamically significant than bigeminy because two of every three beats are conducted normally. Same underlying causes as isolated PACs — stimulants, hypoxia, electrolyte imbalance.