Effect of sequential radiofrequency ablation lesions at fast and slow atrioventricular nodal pathway positions in patients with paroxysmal atrial fibrillation.

OBJECTIVE: To examine the hypothesis that the anatomic equivalents of the fast and slow pathways identified in patients with atrioventricular (AV) nodal tachycardia may be universal and represent the principal sites of atrial input into the normal compact AV node. METHODS: 15 patients undergoing complete AV junction ablation for paroxysmal atrial fibrillation were studied. Radiofrequency energy was delivered first in the anterior "fast pathway" position so as to prolong the atrium to bundle of His (AH) interval by over 50% of baseline (protocol 1) and then to the "slow pathway" position using the anatomical technique (protocol 2). RESULTS: Ablation protocol 1 resulted in prolongation of AH interval in all patients. Subsequent lesions at the level of the coronary sinus produced complete heart block in four patients, and in five caused a further increase in AH interval above that produced by protocol 1. Four of these latter patients developed complete block after delivery of RF energy slightly anterior to the level of the coronary sinus os, as did three further patients in whom ablation at the level of the coronary sinus had no effect. In four patients complete heart block could not be achieved by protocol 2. CONCLUSIONS: A discrete anterior "fast" pathway and a posterior "slow" pathway or network of posterior pathways form the principal inputs to the compact AV node in most patients with atrial fibrillation. The absence of dual AV nodal physiology in the majority of these patients may be related to the functional properties of the individual components of this posterior network.

Shuttle walking test: a new approach for evaluating patients with pacemakers.

OBJECTIVE: To validate an incremental field walking test, the shuttle walking test, as a means of assessing pacing modes and to aid programming of rate responsive pacemakers. DESIGN: Three separate groups of patients were recruited. Reproducibility (n = 10) of the shuttle walking test was assessed by performing three consecutive tests. Comparison of the shuttle walking test with a 10 min walk was assessed in 20 patients. In the third group (n = 10) patients with rate responsive pacemakers were programmed to either VVI fixed rate 70 beats/min or VVIR with the optimal rate response to show the discriminative value of the test. SETTING: Pacing clinic in a regional cardiothoracic centre. PATIENTS: 30 patients with chronotropic competence and dual chamber pacemakers with varying functional capacity and 10 patients with rate responsive pacemakers. INTERVENTIONS: Continuous haemodynamic monitoring was obtained using an ambulatory nuclear monitor, the Capintec VEST. Two exercise tests either shuttle walking test or 10 min corridor walk. The shuttle walk is an incremental walking test conducted on a 10 m course where the walking speed is dictated by bleeps on an audio cassette. RESULTS: Reproducibility was demonstrated over three consecutive tests with mean (1 SD) exercise times of 7.6 (1.7) min, 7.7 (1.6), and 7.7 (1.7) min. During the shuttle walk the test patients walked for a mean of 8.3 (1.2) min producing peak relative cardiac outputs of 78 (21) end diastolic volume/min compared with 64.9 (17) end diastolic volume/min for the 10 min walk (P < 0.001); peak heart rates were 118 and 104 beats/min (P < 0.03) respectively. In the third group relative peak cardiac output was significantly greater in VVIR (70 (24) v VVI 52 (15) end diastolic volume/min) (P < 0.009) as were exercise times (VVIR 8.8 (1.3) min v VVI 8.1 (1.3) min) (P < 0.003). CONCLUSIONS: The shuttle walk is an easy test to administer, requiring little equipment. It produces a symptom limited maximal performance and will be a useful aid to pacemaker programming as it is reproducible and able to show differences in exercise capacity between pacing modes.

An approach in the assessment of pacing hemodynamics: a comparison of VVI and DDD.

Previous methods for assessment of pacemaker hemodynamics have been limited to a rigid hospital environment. An alternative is the ambulatory ventricular function monitor (C-VEST) that, with a single injection of technetium-99m, permits the continuous measurement of relative ejection fraction (EF) and cardiac output (CO) during the activities of daily living. A study of reproducibility and a comparison of dual chamber (DDD) and fixed rate ventricular (VVI) pacing are presented. Reproducibility was assessed in six patients (4 males; mean age 58, range 27-78 years) with a mean EF of 48.5% (range 34%-62%) and DDD pacemakers, implanted for conduction abnormalities. In addition, 11 patients (7 males; mean age 55.5, range 34-75 years) with a mean EF of 48.5% (range 34%-65%), chronic complete heart block, and DDD pacemakers were used for the comparative study. After an initial multigated scan, the monitor was positioned over the left ventricle and kept in place with the plastic C-VEST. The patients undergoing the reproducibility study performed three shuttle walking tests with 20 minutes of rest in between. The patients in the comparative study were randomized to either VVI or DDD mode and performed one shuttle walking test in each pacing mode. The results confirmed that the C-VEST produces reproducible results with no significant difference in peak CO between the three shuttle walks. In addition, it confirmed previous hemodynamic studies showing that DDD pacing was superior to VVI pacing both at rest (P < 0.004) and at exercise (P < 0.002). These findings show the C-VEST to be an extremely useful tool for the hemodynamic assessment of pacemaker patients.

Clinical experience with a new lead combining active fixation with steroid elution.

The Medtronic lead engineering model number 10335A represents a new concept in lead design combining active fixation with steroid elution. It aims for immediate stability and low chronic thresholds. Twenty-one leads, 9 atrial and 12 ventricular, were implanted in 13 patients (10 males, mean age 68; range 22-91 years). The atrial leads showed no rise in pulse width threshold at a voltage of 1.6 volts (mean thresholds at implant, 1, and 26 weeks; 0.1 +/- 0.09 msec, 0.15 +/- 0.04 msec, and 0.1 +/- 0.03 msec, respectively). The ventricular leads had a small but significant rise between implant and 1 week at an output of 1.6 volts (0.07 +/- 0.03 msec increasing to 0.11 +/- 0.04 msec; P < 0.02) but no significant later rise (0.1 +/- 0.04 msec at 2 weeks and 0.1 +/- 0.05 msec at 6 months). These low chronic thresholds would allow early reprogramming of the unit to low voltages resulting in a battery saving with prolongation of the unit's life. There were no significant changes in the P and R wave amplitudes, but there was a fall in lead impedance in the ventricular leads between implantation and 1 week (P < 0.02) but none subsequently, and there was no significant change in atrial impedance. There were no sensing failures and no lead displacements. Despite impressive pacing characteristics, the study was suspended because of a high level of mechanical complications. Of the 96 patients implanted worldwide with 136 leads there were eight helix deformations, which will require redesign.(ABSTRACT TRUNCATED AT 250 WORDS)