Iatrogenic Atrial Tachycardia-dimensional Mapping And Its Mechanism

Objective The purpose of this study was to evaluate the electrophysiological mechanism of atrial flutter after surgical repair procedure (SAFL) and typical atrial flutter (TAFL) by analysis of the cavo-tricuspid isthmus conduction time (CTI-CT) and the conduction velocity of the two groups.Methods Nine patients (47.2±16.9 years, 6 males) with SAFL and eight patients (age 52.0±19.1 years, 7 males) with TAFL received catheter ablation from February 2006 to January 2008 under the guidance of the noncontact mapping system. Three-dimensional geometry of right atrium was reconstructed and the special anatomical landmarks were tagged on the map. After geometry making, the isopotential maps of each tachycardia was created to analyze its activation sequence, reentrant circuit, critical isthmus. Then the tachycardia cycle length (TCL), conduction time and conduction velocity in the cavo-tricuspid isthmus (CTI), the right atrium free wall (RAFW) and atrial septum (AS) of the two groups were measured and compared with each other. The CTI-CT was defined as the conduction time between the seven o'clock of the tricuspid annulus (TV7) and the upper margin of the coronary sinus ostium (CSO). The conduction time of RAFW was defined as the conduction time between TV12 and TV7. The conduction time of AS was defined as the conduction time between CSO and TV12. Conduction velocities in CTI, RAFW and AS were measured by the ratio of the length and the conduction time in each part. Linear ablation was performed in the critical isthmus guided by three dimensional mapping systems to the endpoint of bidirectional block.Results The mean cycle length was 254.3±50.7 ms in SAFL and 219.8±18.9 ms in TAFL. CTI-CT in SAFL was significantly shorter than TAFL (50.5±13.0 ms vs 76.6±11.6 ms) (P < 0.05) while conduction velocity was faster than the latter (0.84±0.15 m/s vs 0.53±0.15 m/s) (P < 0.05 ) . The conduction time was significantly longer (148.4±36.4 ms vs 82.1±28.4 ms) with the conduction velocity slower (0.42±0.14 m/s vs 0.76±0.25 m/s) in RAFW in SAFL group than those in TAFL group (P < 0.05 ) . There was no significant difference in conduction time (55.3±18.5 ms vs 61.1±19.9 ms) and the conduction velocity (0.94±0.29 m/s vs 0.81±0.23 m/s) of AS between the two groups (P > 0.05 ). All the tachycardia was successfully eliminated by catheter ablation guided by noncontact mapping system. After a mean follow up of 10.1±6.6 months,one tachycardia in SAFL group recurred and received a second ablation.Conclusions The slow conduction in the CTI is the basic electrophysiological substrate for TAFL, but in SAFL, CTI is more a critical anatomical isthmus than an electrophysiological isthmus. The slow conduction area of SAFL was located in the RAFW. Objective The purpose of this study is to demonstrate the mechanisms of mitral isthmus dependent atrial tachycardia (MI-AT) after circumferential pulmonary vein isolation (CPVI) for the treatment of atrial fibrillation (AF) and to discuss its ablation strategy.Methods One hundred and twenty-two consecutive patients with AF were treated with CPVI guided by EnSite-NavX and circular mapping catheter, thirty-two of which received a repeat ablation procedure because of recurrent AF or AT. MI- AT was found in eight patients( male 6, mean age 54.9±8.6years) which was confirmed by electrophysiological study and EnSite-NavX three-dimension mapping system. Linear lesion was performed between the ostium of left inferior pulmonary vein and the mitral annulus ( power 35～40 W, temperature 43～45℃, irrigation rate 17～25 ml/ min ). If the complete bidirectional conduction block of mitral isthmus could not be achieved, further ablation would be attempted within the coronary sinus ( power 20～25 W , temperature 43℃, irrigation rate 17ml/ min). Reisolation is necessary when reconduction between pulmonary vein and left atrium was found.Results Three-dimension mapping showed clockwise activation going around mitral ring in five patients while counterclockwise activation in three patients. The mean cycle length of MI-AT was 217.5±20.6 ms. Bidirectional block of mitral isthmus was obtained in five patients after endocardial linear lesions. The left three patients which were failed by endocardial approach had coronary sinus attempt with only one success. After a mean follow up of 5.5±4.3 months, six patients were free of AT or AF attack, one patient still had paroxysmal AT, another patient developed incessant AT and had the medication of Amiodarone and Metoprolol to control the heart rate.Conclusions MI-AT can be developed because of the proarrhythmia effect of CPVI for the treatment of AF and also be due to macro-reentrant induced by incomplete lines or recovery conduction. Bidirectional block of the mitral isthmus can be achieved by liner ablation between the ostium of left inferior pulmonary vein and the mitral annulus. In some patients, additional ablation should be attempted within coronary sinus. But this endpoint could not be always obtained even after the joint ablation approach both endocardially and epicardially.