Elucidating the Mechanisms of Atrial Flutter Cycle Length Variability Using Power Spectral Analysis Techniques

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Abstract
Background The mechanism of the small beat-to-beat variations in cycle length of atrial flutter in humans has not been fully explained. We investigated the beat-to-beat control of atrial flutter cycle length using time and frequency analysis techniques. Methods and Results Mean, SD, and power spectra of atrial cycle lengths were calculated from atrial recordings in 28 patients with type I atrial flutter. In control patients, mean and SD values of atrial cycle length were 265±37 and 4.9±1.7 ms. Power spectra contained two or three major peaks with 10.6±9.2% in band 1 (0.0 to 0.18 Hz), 26.7±15.9% in band 2 (0.18 to 0.6 Hz), and 63.1±17.7% in band 3 (0.6 to 2.2 Hz). Isoproterenol infusion (n=8) increased percentage of total power in band 1 (7.1±5.6% to 25.7±18.9%, P <.001). Percentage of total power in band 1 was less in patients receiving (n=5) versus not receiving (n=18) oral β-blockers (2.2±1.9% versus 10.6±9.2%, P =.003). Standard deviation (2.5±1.3 versus 4.9±1.7 ms, P =.009) and total power (2025±1350 versus 9768±8874 ms 2 , P =.005) were less in heart transplant recipients (n=5) than control patients. Increases in respiratory rate (n=6) shifted band 2 frequency peak to higher frequencies (0.26±0.13 to 0.38±0.18 Hz, P <.05). Atrial cycle length was longer and monophasic action potential duration was shorter during inspiration than during expiration. Band 3 frequency peak was correlated with heart rate ( r =.797, P <.0001). Conclusions Atrial flutter cycle length variability has an underlying periodic pattern that is detected by spectral analysis. Atrial flutter is modulated on a beat-to-beat basis by an interplay between the autonomic nervous and respiratory systems and the ventricular rate.

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