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Objectives The objective of this study is to analyze the relationship between atypical ECG patterns in typical atrial flutter (AFL) and cardiac structure, as well as sinus rhythm P-wave parameters. Materials and methods 389 consecutive patients diagnosed with typical AFL who were treated at our center were included. The morphology of the flutter wave was assessed in each lead. Counterclockwise AFL could be classified into three typical groups and two kinds of atypical groups based on the flutter ECG patterns. Sinus rhythm P-wave parameters, including PtfV1 ( P Wave Terminal Force of V1 ), P-wave area, axis, and interatrial block (IAB), etc. were measured manually. The analysis focused on examining the correlation between flutter wave and atrial structure characteristics, as well as the influence of prior cardiac surgery. Furthermore, an analysis was conducted on the correlation between P-wave parameters and F-wave morphology. Results The size of the atrium and previous cardiac surgery have an impact on the AFL ECG pattern. P-wave amplitude in lead II ( p  < 0.0001), lead III ( p  < 0.0001), V1 terminal interval ( p  = 0.01), and P-wave area ( p  < 0.0001) exhibited significant differences between the typical and atypical groups. Furthermore, the SR P-wave axis and the presence of IAB may also be associated with an atypical AFL pattern. Conclusion Typical AFL may exhibit various ECG patterns and two new patterns were found. SR P-wave, such as IAB and P wave amplitude, duration, etc. has the potential to predict atypical ECG patterns in typical AFL. The size of the right atrium significantly influence the characteristic ECG patterns observed in typical AFL.