Three-dimensional noncontact mapping defines two zones of slow conduction in the circuit of typical atrial flutter.

The cavotricuspid isthmus (CTI) is a slow conduction area in the circuit of typical atrial flutter. However, conventional methods are limited by the inaccuracy of measurements of distance on the surface of the heart. The aim of the study was to define the conduction properties of the atrial flutter circuit along the tricuspid annulus by using a three-dimensional noncontact mapping system. In 34 atrial flutter patients (30 men, 4 women; mean age 54 +/- 14; 27 counter-clockwise, 4 clockwise, and 3 both), a noncontact multielectrode array was used to reconstruct electrograms in the right atrium. Isochronal and isopotential propagation mapping was performed during atrial flutter. The conduction velocity was calculated by dividing conduction time by surface distance. The right atrium along the tricuspid annulus was divided into five regions: lateral wall, superior right atrium, septum, septal CTI, and lateral CTI. Conduction velocities were 0.99 +/- 0.85, 1.67 +/- 1.21, 1.58 +/- 1.05, 0.82 +/- 0.72, and 1.68 +/- 1.00 m/s in counter-clockwise and 0.81 +/- 0.71, 2.61 +/- 1.90, 1.52 +/- 0.91, 0.91 +/- 0.80 and 1.91 +/- 0.83 m/s in clockwise, respectively. Conduction velocities were significantly slower in the septal CTI and lateral wall than in the lateral CTI, the septum, and the superior right atrium (P < 0.05). No significant difference was found between the septal CTI and the lateral wall. Conduction within the septal CTI was slower in patients treated with antiarrhythmic agents than in untreated patients (P < 0.05). The septal part of the CTI (but not the lateral CTI) and the lateral wall are slow conduction zones in the atrial flutter circuit, and both may, therefore, be mechanically important for the development of atrial flutter.