Radiofrequency Current Ablation of Porcine Right Atrium: Increased Lesion Size with Bipolar Two Catheter Technique Compared to Unipolar Application In Vitro and In Vivo

Interruption of atrial flutter and fibrillation by RF catheter ablation may be favored by large, elongated lesions. We administered RF current in unipolar and bipolar mode in porcine right atrium. Bipolar ablation was performed between the tip electrodes of two serially coupled catheters. With 4-mm tip electrodes in vitro, lesion length increased from a mean (SD) of 7.9 (1.2) mm at 3 mm-interelectrode distance (IED) to 13.3 (3.3) mm at 9-mm IED, but decreased at 12-mm IED due to nonconfluent lesions (P < 0.0001), With 4 mm distal electrodes and 8 mm IED, bipolar lesions were 65% longer than corresponding unipolar ablations. Switching to bipolar mode increased the lesion length more than increasing electrode tip length to 6 mm in unipolar mode. Power and temperature controlled ablation created equally sized lesions. Twelve anesthetized pigs were randomized to unipolar or two catheter bipolar temperature controlled ablation of the right atrial free wall. Bipolar ablation created confluent lesions with endocardial length × width of 13.5 (5.8) × 7.3 (3.7) mm, unipolar ablation 6.4 (2.8) × 4.6 (1.4) mm (P < 0.001 when comparing length and P = 0.013 for lesion width). The atrial lesions in both groups were transmural and extended into hilar lung lesions with maximal depth of 3.0 (1.1) and 2.6 (1.0) mm, respectively (P = 0.44). Five bipolarly and four unipolarly ablated pigs developed right diaphragmal paresis. We conclude that bipolar ablation may be preferable in situations where large, elongated lesions are favorable. The two catheter technique is feasible in porcine right atrium. Both bipolar and unipolar ablation of the porcine right atrial free wall may frequently be complicated by injury to the phrenic nerve and adjacent lung tissue.     

Of mud and alligators

Each year Dr Mahler, Director-General of the World Health Organization,presents a report to member country delegates at the World HealthAssembly. In his address this year, he likened WHO's attemptsto promote primary health care (PHC) and Health for All by theYear 2000 to being in a swamp, ‘up to our necks in verbalmud, fighting all sorts of conceptual alligators’. Yetthe aim is to clear the swamp. We reproduce here most of thataddress, not only for its lively images, but also because init Dr Mahler takes on some of the conceptual and other criticismsof PHC, recapitulates what it is all about, casts a dear eyeover how countries are faring in their implementation of PHC,and outlines some suggested areas for action in the coming years.Going back to first principles, he argues that PHC starts withpeople, their health problems, and their active involvementin solving those problems. It is that active involvement thatdistinguishes PHC from past health policies. It is not by chancethat the very first element of PHC is educating people and communitieson health matters, because for people to be intelligently involvedin caring for their own health, they have to understand whatleads to health and what endangers it. A crucial point is emphasized-thatit is people themselves who decide what kind of care is requiredand not outsiders. In reviewing action programmes for PHC, DrMahler emphasizes the need for good organization and management,and calls for efforts to be concentrated on building up districtinfrastructures, with defined targets to galvanize people intoaction. He makes a number of suggestions for setting realistictargets and deciding what appropriate technologies exist thatcan be appropriately applied. The speech is a useful policypointer on the road to Health for All by the Year 2000.     

Power and Temperature Guided Radiofrequency Catheter Ablation of the Right Atrium in Pigs

The aim of the present study was twofold: to assess the safety of ablating the atrial free wall using RF current; and to assess the effect of a single dose of intravenous beparin foUowed by aspirin once daily to prevent tbrombas formation after RF ablation. Temperature and power guided catheter ablation were evaluated. Twenty pigs were randomized to power or temperature guided unipolar RF catheter ablation. Ten animals received a bolus of beparin (150 U/kg) followed by 150-mg aspirin daily. and ten served as controls. A mid-sternal tboracotomy was performed 5–7 days later. the ability of a lesion to resist an increased transmural atrial pressure was examined by inflating a cuff around the palmonal artery. Transmurai lesions were found in all animals. Rigbt atrial pressure was increased from 5 to 30 mmHg witb no sign of perforation. In 11 of 20 (55%) animals, 1–3 lesions were foand in the lungs (diameter 4–18 mm). the localization of these lesions corresponded to the lesions in the atria. there were no differences in the energy delivery modes witb regard to the number of animals witb lung lesions. Lesions witb thrombus formation were found in four animals in the heparin/aspirin group and in nine animals in the control group. The incidence of thrombi was significantly smaller in the treatment group. there were no differences between temperature and power guided catheter ablation witb regard to the size of the atrial lesions or to the incidence of tbrombus formation. Transmural lesions induced in the rigbt atrium by RF energy are resistant to increases in transmural pressure. However, lung tissue overlying the ablated target may be injured by the RF energy delivered. The combination of a single dose intravenous beparin followed by aspirin daily may reduce the incidence of tbrombus formation.     

Effects of combined radiofrequency and direct current energy catheter ablation on ventricular myocardium in pigs

When radiofrequency catheter ablation of ventricular arrhythmiasis unsuccessful, an option may be to combine it with directcurrent energy. We therefore investigated the effects of sucha combination. Radiofrequency energy was delivered in a bipolar or unipolarfashion to the left and right ventricles through an ablationcatheter with a tip electrode 2 mm long, using a temperature-guidedradiofrequency generator. Radiofrequency ablation was followedby a single cathodal direct current shock (66 J) with the ablationcatheter positioned similarly in six closed-chest pigs. In acontrol group (six animals) only direct current ablation wasperformed, with one or two energy applications (66 J) in eachventricle. Two of six animals in the radiofrequency I direct current groupdied due to perforation in the follow-up period, 1 and 3.5 hafter the direct current ablation, respectively. Gross pathologicalexamination of the hearts revealed transmural lesions in allanimals. In the radiofrequency I direct current group four lesionswere perforated, three of which were located in the left ventricle.There was a significant increase in the number of perforationsin the radiofrequency/direct current group compared to the controlgroup, where perforation was never observed Haemorrhagic pericardialfluid was found in five of the six animals in the radiofrequency/directcurrent group compared to none in the control group. These findings show that myocardial ablation with radiofrequencyenergy followed by direct current energy in the same sessionmay have a high complication rate.     

Temperature Guided Radiofrequency Catheter Ablation of Myocardium: Comparison of Catheter Tip and Tissue Temperatures In Vitro

Temperature monitoring during RF ablation has been proposed as a means of controlling the creation of the lesion. However, in vivo studies have shown poor correlation between lesion size and catheter tip temperature. Thus, we hypothesized a difference between catheter tip and tissue temperatures during RF catheter ablation, and that this difference may depend on flow passing the ablation site, tip electrode length, and catheter-tissue orientation. In vitro studies were performed using four different ablation catheters (tip electrode length: 2, 4. or 6 mm) with a thermistor or a thermocouple as temperature sensor. Set temperature was 70°C and pulse duration was 30 seconds. Pieces of porcine left ventricle were immersed in a bath of isotonic saline-dextrose solution at 37°C. The ablation catheters were positioned perpendicularly, obliquely, or parallel to the endocardium. A temperature sensor was inserted from the epicardial side and positioned 1 mm beneath the catheter-tissue interface. Experiments were made with a flow of 200 mL/min passing the ablation site or with no flow. The catheter tip and tissue temperatures differed significantly (P < 0.0001) during ablation. This difference increased with time, with flow passing the ablation site, with the length of the tip electrode, and when the catheter was positioned perpendicularly or obliquely to the endocardium as compared to the parallel catheter-tissue orientation (P < 0.05), In conclusion, the tissue temperature may far exceed the catheter tip temperature, and intramyocardial superheating resulting in steam formation and popping may occur despite a relatively low catheter tip temperature. (PACE 1997; 20[Pt. I]:1252-1260)     

The Activation of Platelet Function, Coagulation, and Fibrinolysis during Radiofrequency Catheter Ablation in Heparinized Patients

INTRODUCTION: Catheter ablation may be complicated by clinical thromboembolism in about 1% of patients. METHODS AND RESULTS: We studied the activation of coagulation (prothrombin fragment 1+2 [PF1+2]), platelets (beta-thromboglobulin [beta-TG])) and fibrinolysis (plasmin-antiplasmin complexes [PAP] and D-dimer) during radiofrequency (RF) ablation in 13 patients. They received heparin 100 U/kg intravenously after the initial electrophysiologic study, prior to the delivery of RF current; thereafter 1,000 U/hour throughout the procedure. PF1+2 increased fourfold (P < 0.001) during the diagnostic study, but gradually declined to upper reference value during heparin administration. There was a strong correlation between procedure duration prior to heparin bolus (range 39 to 173 min); and (a) the maximal rise of PF1+2 (r = 0.83, P < 0.001) and (b) the increase of PF1+2 from baseline to end of the procedure (r = 0.74, P = 0.004). There was no correlation between postheparin changes of PF1+2 and (a) postheparin procedure duration (range 40 to 317 min), (b) number of RF pulses (range 1 to 16), or (c) RF current duration (range 46 to 687 sec). Plasma beta-TG concentration showed similar trends. Fibrinolytic activity increased moderately from baseline until heparin administration; then remained around the upper reference values. PAP at the end of procedure and D-dimer at the time of heparin administration both correlated with preheparin procedure duration (r = 0.70, P = 0.007 and r = 0.69, P = 0.01, respectively). All parameters were normal the next morning. CONCLUSION: Procedure duration prior to heparin administration, and not the delivery of RF current per se, determines activation of hemostasis and fibrinolysis during RF ablation.     

INTRAOCULAR AND INTRACRANIAL PRESSURE DURING RESPIRATORY ALKALOSIS AND ACIDOSIS

Intraocular and intracranial pressures (IOP and ICP) were measuredat four different arterial carbon dioxide tensions by directcontinuous techniques in Rhesus monkeys during anaesthesia withhalothane and nitrous oxide. Increases in IOP correlated significantlywith Pa_co2. ranging from 2.66 to 10.24 kPa (P<0.001). Increasesin ICP correlated significantly (P<0.001) with Pa_co2 between2.66 and 7.71 kPa, but plateaued thereafter. When Pa_co2 wasdecreased rapidly, Pa_co2, IOP and ICP decreased exponentiallywith similar half-times. The fast changes in IOP and ICP canprobably be explained by an alteration of intraocular and intracranialblood volumes. IOP usually remained within the normal range,even at maximum Pa_co2.