| Objective: Epicardial mapping of LOM was performed by a home-made comb-like mapping catheter, to elucidate electrical characters of ligament of Marshall (LOM) and it' s relationship with left atria, coronary sinus (CS), left pulmonary veins and to evaluate the effects of chemical ablation to LOM potential,.Methods: A total of 19 normal dogs with both genders (weight 15-21 kg )were adopted in this study . After general anesthesia with sodium pentobarbital (30mg/kg im) (stop feeding 12 hours before procedures), these animals were intubated and mechanically ventilated with a pressure-controled ventilator. A left intercastal space thoarecotomy was performed, and 1 or 2 ribs were removed according to the degree of exposure. Pericardium was opened to cradle the heart. Then the LOM and pulmonary veins were clearly exposed. Epicardial mapping of the LOM was registered with comb-like mapping catheter closely paralleling to the LOM near left super pulmonary vein and the tenth pole was laid over CS entrance of LOM. Then the comb-like mapping catheter was paralleled to LOM and moved to left atrial appendage (LAA) or left pulmonary veins for about 2 mm and 5 mm respectively. Then the comb-like mapping catheter was paralleled toCS and the tenth pole was located to the orifice of CS. S1S1 programmed stimulations were applied to the first electrode of the comb-like mapping catheter, LAA, LSPV respectively and chemical ablation was applied to the CS entrance of LOM. Every procedure was accompanied by synchronously recording of surface ECG (lead II) and 9-channel, bipolar epicardial electrogram.LOMs of six dogs were cutted off from mid segments to observe the changes of LOM potential and effective refractive period of LOM before and after cutted off respectively.The effective refractive period of LOM was compared and statistically analyzed before and after the cutting off and a =0. 05 was considered as significance level.Results:1. Registrable rate of LOM potential: LOM potential in 17 dogs could be registered among the 19 dogs and the registrable rate is about 89. 5 percents (17/19).2. Characteristics of bipolar epicardialgram of LOM: Every bipolar epicardial gram consists of corresponding left atrial potential and LOM potential .The left atrial potential of 10 bipolar epicardialgrams gradually delay from top to bottom under sinus rhythm. LOM potentials gradually precede from top to bottom in 10 dogs . So at the CS entrance of LOM, the typical "V" figure was composed by the left atrial potential and the LOM potential. In another 7 dogs, the LOM potentials gradually precede from top to bottom. But the earliest LOM potential is recorded at both at the middle segment and at the CS entrance of LOM. So atypical"V" shape (like "Y" ) was presented. The synchronously recorded 9 channels epicardialgram along the LOM presented as a typical "V" figure in 58. 8% (10/17) and presented as an atypical "V" figure in 41. 2% (7/17).3. Electrical relationship between LOM and CS: Double directionelectrical conduction were presented in 94. 1%(16/17). The width of recordable region of LOM potential was about 4~8mm at the CS entrance of LOM.4. Comparison of the LOM potential' s changing by alcohol ablation: The LOM potential could entirely disappeared by injecting alcohol only to the CS entrance of LOM in 9 dogs whose LOM bipolar epicardiogram were"V" figure among 11 consecutive dogs intervened by ablation with injection of alcohol. Then the electrical isolation of LOM was realized and the success rate of first ablation was 77. 8%. For another 2 dogs whose LOM bipolar epicardiogram were "Y" figures, the electrical isolation could not be realized by the alcohol ablation at the CS entrance of LOM, it should be realized together by the ablation to the middle segment of LOM (left atrial free wall entrance of LOM). The total successful rate of alcohol ablation can achieve 100 percent.5. The effective refractive period of LOM has no change before and after the cutting off (S1S2=400/115. 00 + 7. 07ms VS 400/115. 83 + 3. 76ms, P>...
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