Short- and long-term effects of transcatheter ablation of the coronary sinus by radiofrequency energy

Radiofrequency ablation: technological trends, challenges, and opportunities

More than three decades have passed since utilization of radiofrequency (RF) ablation in the treatment of cardiac arrhythmias. Although several limitations and challenges still exist, with improvements in catheter designs and delivery of energy the way we do RF ablation now is much safer and more efficient. This review article aims to give an overview on historical advances on RF ablation and challenges in performing safe and efficient ablation.

Epicardial Ablation via Arterial and Venous Systems

The intracoronary artery and venous routes provide unique roadmaps for mapping and interventions for ventricular arrhythmias and certain atrial arrhythmias. The unique anatomic location of these vessels on the epicardial surface enables mapping/interventions without the need to access the pericardial space. These anatomic routes also track deep into certain intramural regions, with interventions that are not accessible from either epicardial or endocardial routes. To map smaller vessels, multipolar catheters and wires are used to record local electrograms. Endocardial/epicardial ablation at adjacent sites is sometimes required to enhance successful outcomes. This article describes tools, techniques, and site-specific mapping and interventions.

Radiofrequency ablation of coronary sinus-dependent atrial flutter guided by fractionated mid-diastolic coronary sinus potentials

Background

The efficacy of radiofrequency (RF) ablation of an uncommon coronary sinus (CS)-dependent atrial flutter (AFL) was evaluated using conventional electrophysiological criteria in a highly selected subset of patients with typical and atypical AFL.

Methods

Fourteen patients with atrial flutter (11 males, mean age 69 ± 9 years) without previous right or left atrial RF ablation were included. Heart disease was present in eight patients. Baseline ECG suggested typical AFL in 12 patients and atypical AFL in two. Mean AFL cycle length was 324 ± 64 ms at the time of RF ablation in the CS. Lateral right atrium activation was counterclockwise (CCW) in 13 patients and clockwise in one. CS activation was CCW in all. Criteria for CS ablation included the presence of CS mid-diastolic fractionated atrial potentials (APs) associated with concealed entrainment with a postpacing interval within 20 ms. Success was defined as termination of AFL and subsequent noninducibility.

Results

The initial target for ablation was the cavotricuspid isthmus (CTI) in 11 patients and the CS with further CTI ablation in three. AP duration at the CS target site was 122 ± 33 ms, spanning 40 ± 12% of the AFL cycle length. CS ablation site was located 1–4 cm from the CS ostium. Ablation was successful in all patients. Mean time to AFL termination during CS ablation was 39 ± 52 s (<20 s in eight patients). No recurrence of ablated arrhythmia occurred during a follow-up of 18 ± 8 months.

Conclusions

The CS musculature is a critical part of some AFL circuits in patients with typical and atypical AFL. AFL can be terminated in patients with CS or CTI/CS AFL reentrant circuits by targeting CS mid-diastolic fragmented APs.

Feasibility of myxomatous mitral valve repair using direct leaflet and chordal radiofrequency ablation

OBJECTIVE

Minimally invasive repair of mitral valve prolapse (MVP) causing severe mitral regurgitation (MR) should reduce MR and have chronic durability. Our ex vivo, acute in vivo, and chronic in vivo studies suggest that direct application of radiofrequency ablation (RFA) to mitral leaflets and chordae can effect these repair goals to decrease MR.

METHODS

A total of seven canines were studied to assess the effects of RFA on mitral valve structure and function. RFA was applied ex vivo (n = 1), acutely in vivo using a right lateral thoracotomy and cardiopulmonary bypass (n = 3), and chronically in vivo using percutaneous access to the heart (n = 3). RFA was applied to the mitral valve and its associated chordae. Mitral valve structure and function (in vivo preparations) were then assessed.

RESULTS

Ex vivo application of RFA resulted in qualitative reduction in mitral leaflet surface area and chordal length. Acute in vivo application of RFA to canines found to have MVP causing severe MR demonstrated a 43.7-60.7% statistically significant (P = 0.039) reduction in postablation MR. Chronic, in vivo, percutaneous application of RFA was found to be feasible and the engendered alterations durable.

CONCLUSION

These data suggest that myxomatous mitral valve repair using radiofrequency energy delivered via catheter is feasible.

Fate of left atrial function as determined by real-time three-dimensional echocardiography study after radiofrequency catheter ablation for the treatment of atrial fibrillation

Radiofrequency catheter ablation has been demonstrated to be effective in the treatment of patients with atrial fibrillation. However, its impact on left atrial (LA) function has not been widely studied. The purpose of the present study was to evaluate the impact of radiofrequency catheter ablation on LA function in patients with atrial fibrillation. Thirty-eight patients with symptomatic drug-refractory atrial fibrillation were treated with circumferential pulmonary vein ablation (CPVA). LA volumes and function were assessed with real-time 3-dimensional echocardiography before and 6 months after the procedure. The effectiveness of CPVA was evaluated at 6-month follow-up. Recurrence of the arrhythmia was defined as any documented (clinically or on 24-hour Holter electrocardiography) atrial tachyarrhythmia lasting>30 seconds after the first 12 weeks after the procedure. CPVA induced a reduction of maximum LA volume (from 55+/-15 to 48+/-16 ml, p<0.001), without impairment in LA function, measured as the active emptying percentage of total volume (32+/-29% vs 39+/-33%, p=NS). At follow-up, 21 patients (61.8%) had no recurrences. Maximum LA volumes were significantly larger in patients who presented with recurrences compared with those who did not (64+/-18 vs 50+/-11 ml, p=0.01). In conclusion, CPVA induces a reduction in LA volume without a deleterious impact on function, and, of importance, real-time 3-dimensional echocardiography is a useful noninvasive imaging tool to follow up LA remodeling and function in these patients.

Intra-coronary guidewire mapping–A novel technique to guide ablation of human ventricular tachycardia

HYPOTHESIS

Endocardial catheter ablation of ventricular tachycardia (VT) may fail if originating from epicardial or intramural locations. We hypothesized that mapping could be achieved using an angioplasty guidewire in the coronary circulation, to guide trans-coronary ablation.

METHODS AND RESULTS

Six patients (2 male), 64 +/- 14 years and previously unsuccessful endocardial VT ablation were studied. Using ECG and existing endocardial mapping data, a coronary artery supplying the predicted VT origin was selected. A 0.014-in angioplasty guidewire was advanced into branches of the artery and connected to an amplifier to record unipolar signals against an indifferent electrode within the inferior vena cava. An uninflated angioplasty balloon was advanced over the wire such that only the distal 5 mm was used for mapping. One VT per patient was mapped (CL 348 +/- 102.1 ms). Diastolic potentials were recorded from all (77.7 +/- 43.8 ms pre-QRS onset) and concealed entrainment demonstrated in 3. Pacemapping during sinus rhythm was used in the remainder due to failure of entrainment (n = 2) or degeneration to VF (n = 1). Following branch identification, cold saline injection causing VT termination was used for further confirmation. Five VTs were ablated using intra-coronary ethanol injection via the central lumen of the inflated over the wire balloon. The other was ablated using radiofrequency energy in a coronary vein adjacent to the target artery, which was too small for an angioplasty balloon. No complications or recurrence of ablated VT was seen over 19 +/- 17 months of follow up.

CONCLUSIONS

Intracoronary guidewire mapping is a novel method of electrophysiological epicardial mapping to help guide trans-coronary VT ablation.

Acute and Chronic Effects of Extensive Radiofrequency Lesions in the Canine Caval Veins: Implications for Ablation of Atrial Arrhythmias

BACKGROUND

Although radiofrequency (RF) ablation within the caval veins has been increasingly used to treat a variety of atrial tachyarrhythmias, the consequences of RF ablation in the caval veins are unknown. We explored the acute and chronic angiographic and pathological effects of extensive RF ablation in the caval veins.

METHODS

Under fluoroscopy guidance, conventional (4 mm tip, 60 degrees C, 60 seconds) RF applications (n = 6-7) were delivered in each vena cava (from +/-2 cm into the vein to the veno-atrial junction) of 15 dogs (10 +/- 3 kg). Animals were killed 1 hour and 5 weeks after ablation for histological analysis. Angiography was performed before ablation (acute dogs only) and at sacrifice to assess the degree of vascular stenosis.

RESULTS

In acute dogs (n = 5), luminal narrowing was noted in 10/10 (100%) targeted veins (mild in two; moderate in three and severe in five, including two total occlusions). In the six chronic animals that completed the protocol (four died during follow-up), stenosis was also observed in 12/12 (100%) ablated veins (mild in six; moderate in four and severe in two). Of these, one superior vena cava was suboccluded with development of extensive collateral circulation. Histologically, acute lesions displayed typical transmural coagulative necrosis, whereas chronic lesions revealed intimal proliferation, necrotic muscle replaced with collagen, endovascular contraction, and disruption and thickening of the internal elastic lamina.

CONCLUSION

In this model, extensive RF ablation in the caval veins may result in significant vascular stenosis. These findings may have implications for catheter ablation of arrhythmias originating within the caval veins.

Change in Size of Lesions Over 3 Weeks After Radiofrequency Ablation of Left Ventricle

INTRODUCTION

The initial success or failure of radiofrequency ablation (RFA) does not always reflect the long-term outcome that can lead to complications such as late atrioventricular block or recurrence of accessory pathways. We hypothesize that these occurrences may be due to a change in lesion size over time.

METHODS AND RESULTS

Intramural RFAs were performed on five greyhounds at thoracotomy using an epicardial approach into the left ventricular (LV) wall. Twenty-one gauge needle electrode ablations were created in the anterior aspect of the left ventricle. Radiofrequency energy was delivered at 600 Hz for 60 seconds and at an electrode temperature of 90 degrees C. Eight ablations were created in each greyhound and the chest was closed. After 3 weeks, a further eight ablations were created under the same conditions in the lateral aspect of the LV, ensuring they were well away from the chronic lesions, and the dogs were sacrificed an hour later. All lesions were removed, stained with Gomori Trichrome and measured. There was no significant difference in lesion size detected in the 1-hour-old lesions compared with 3-week-old lesions. Acute lesions were well demarcated by an area of fibrous scar and a central necrotic region. Chronic lesions showed chronic inflammatory cells and strands of collagen.

CONCLUSIONS

This study shows no change in lesion dimension over time and hence a change in size may not contribute to a change in RFA outcome over time.

Ablation of atrial-ventricular junction tissues via the coronary sinus using cryo balloon technology

INTRODUCTION

The coronary sinus (CS) can provide access to targets across and within the atrioventricular (AV) junction.

METHODS

In 12 dogs (32 +/- 3 Kg), cryo balloons (10-19 mm) were applied to regions of the AV junction for 3 minutes at a temperature of -75.9( composite function) +/- 9(composite function)C (ranging -57 to -83). Electrical activity and pacing within the CS were assessed pre and post ablation and at least 3 months later in 9 dogs. In the 3 other dogs, hearts were examined immediately after cryo ablation. CS and circumflex angiography was performed pre and post ablation. The hearts, CS, and Cx were then examined for structural injury. The AV junction was sectioned and the hearts were immersed in Tetrazolium, and the lesions were inspected for transmurality across the AV groove.

RESULTS

In 3/12 dogs the distal CS cryo lesions resulted in inferior ST segment depression that resolved within 5 minutes. There was no arrhythmia or hemodynamic changes. No CS electrical activity was noted post ablation. The pacing threshold increased from 2 +/- 2.3 mA to 7.4 +/- 3.6 mA (p < 0.001). Pathological examination of 3 acute hearts revealed hematomas. There was no pericardial effusion. No evidence of stenosis or thrombosis was seen within the CS and the circumflex artery. After 3 months of recovery, transmural lesions across the AV groove were present in all of the targeted AV regions.

CONCLUSION

Intra-CS cryo balloon ablation is safe and can potentially replace endocardial RF ablation targeting the AV junction and the CS muscular sleeve.

Histopathology of intraoperatively induced linear radiofrequency ablation lesions in patients with chronic atrial fibrillation

AIMS

Radiofrequency (RF) energy has been extensively used in ablation of arrhythmia but so far no analysis of morphological effects in human left atria has been conducted.

METHODS AND RESULTS

We studied 59 ablation lesions from seven patients who died 2 to 22 days after open heart surgery plus intraoperative cooled-tip RF ablation to treat permanent atrial fibrillation (AF) (mean 4, 1-11 years). The ablation area was studied by macroscopy and histological analysis. RF ablation produced clearly delineated coagulation necrosis (up to a depth of 5.5 mm) bordered by an irregular zone of incomplete necrosis and fresh bleeding even 22 days post-operatively. No superficial charring, thrombotic deposition, or perforation was documented. Endocardium and subendocardium displayed oedematic loosening and microfragmentation of connective tissue fibres. Early after ablation (2-6 days), interfibrillar disseminated bleeding and necrosis without tissue removal response were found. Later after ablation (21, 22 days), mild inflammatory reaction and granulation tissue appeared. Twenty-five per cent of all studied lesions, especially in the thick region in between left pulmonary veins and mitral annulus (left atrial isthmus) (86%), were non-transmural. Nerve fibres with different degrees of thermal injury were detected in the pulmonary vein ostial region.

CONCLUSION

Intraoperative cooled-tip ablation in AF resulted in coagulation necrosis of endocardium, subendocardium, and the atrial myocardial layer to a depth of 5.5 mm bordered by an irregular zone of incomplete thermal damage. Transmurality of the lesions could only be found in 75% of intraoperatively applied lesions.

Saline Irrigated Catheter Ablation for Pulmonary Vein Isolation in Pigs:. An Experimental Model

Focal AF is amenable to radical cure by RF ablation within the PV. The primary purpose of this study was to compare lesion characteristics for irrigated versus standard ablation using three power settings for PV isolation in pigs. Secondary analyses were the comparisons of ablation time and temperature characteristics, and evaluation of short-term safety in the pig model. In 20 pigs from 25 to 35 kg in weight, transseptal catheterization was performed and then the ablation catheter was advanced into the PV. RF energy was delivered to the ostium of the PV until its isolation was achieved. The animals were euthanized 1 week after ablation for pathological examination. Electrophysiological isolation of the PV was achieved, although it was difficult to achieve a complete circumferencial lesion in the ostium of the PV. Both of these catheters can produce transmural necrosis, even using 15 W of power. The authors did not see any stenosis of the PV. This might be due to the low energy delivery and the short follow-up. Pulmonary hemorrhage was present in two animals with 50 W of power, high energy output is dangerous for the ablation of the PV.

Combined Therapy with Steroids and Antioxidants Prevents Ultrastructural Damage Surrounding Chronic Radiofrequency Lesions

We evaluated the effects of combined therapy with anti-inflammatory and antioxidant drugs on the healing of radiofrequency (RF) lesions (70 degrees C, 60 s) produced in the right atrium and each ventricle of 21 adult dogs. Three groups were studied: acute (n= 7, sacrificed 1 hour after RF); control (n = 7, sacrificed 54 +/- 29 days after RF); and dogs (n = 7, sacrificed 32 +/- 5 days after RF) receiving combined therapy with allopurinol (400 mg p.o. 24 and 2 hours before RF); verapamil (200 microg/kg i.v. 15 min before and after RF); hydrocortisone (10 mg/kg i.v. after RF) and prednisone (20 mg p.o. for 29 days). Atrial (n = 37) and ventricular (n = 70) lesion dimensions were determined and 21 right ventricular apex lesions (1 per dog) were selected for light and electron microscopy analysis. Histological and ultrastructural (US) characteristics in three zones extending from the visible lesion border, A (0-3 mm); B (3-6 mm); and C (6-9 mm), were assessed. In chronic groups, atrial and ventricular lesion dimensions were similar, but delayed scar formation was noted in treated animals. Acutely and at follow-up, significant US abnormalities occurred in zones A and B and chronic lesions exhibited type I collagen proliferation. In Zone A, the extent of US injury and collagen proliferation was significantly less in treated dogs. Further, Zone B was normal in 5/7 (71%) treated dogs and in 0/7 (0%) controls. Zone C was essentially normal in all groups. Combined therapy with steroids, verapamil, and allopurinol is effective in limiting US damage surrounding chronic RF lesions.

Origin of Electrical Activation Within the Right Atrial and Left Ventricular Walls:. Differentiation by Electrogram Characteristics Using the Noncontact Mapping System

Clinical data using the noncontact mapping system (Ensite 3000) suggest that characteristics of the reconstructed unipolar electrograms may predict the origin of electrical activation within the atrial and ventricular walls (endocardial vs myocardial vs epicardial origin). Experimental data are lacking. In ten open-chest pigs (mean body weight 62 kg) cardiac pacing was performed at a cycle length of 600 ms with a pulse width of 2 ms and twice diastolic threshold from the endo-, the myo-, and the epicardium, respectively. Pacing was undertaken at three right atrial and three left ventricular sites, and cardiac activation was recorded with the Ensite system. Reconstructed unipolar electrograms at the location of earliest endocardial activation assessed by color coded isopotential maps were analyzed systematically for differences in morphology. The positive predictive value of atrial electrograms exhibiting an initial R wave during pacing for a subendocardial origin (i.e., myocardial or epicardial) was 0.96. The negative predictive value was 0.48. Electrograms generated during myocardial pacing exhibited increased maximal negative voltage and maximal dV/dt (-3 +/- 1.8 mV, -798 +/- 860 mV/ms, respectively) than the electrograms obtained during endocardial (-2 +/- 1 mV, -377 +/- 251 mV/ms, respectively) and epicardial pacing (-2.1 +/- 0.7 mV, -440 +/- 401 mV/ms, respectively, P<0.01 for both parameters). During pacing at the left ventricular wall, occurrence of an initial R wave did not differ significantly between electrograms reconstructed during endocardial and subendocardial pacing. All other characteristics of the unipolar ventricular electrograms analyzed, except latency, did not differ significantly when compared to stimulation depth. Morphological characteristics of unipolar electrograms generated by the noncontact mapping system during pacing of the atrium allowed for discrimination of an endocardial versus a subendocardial origin of activation. At the ventricular level, characteristics of unipolar electrograms did not predict the origin of cardiac activation in this experimental setting.

Successful implantation of a coronary sinus lead after stenting of a coronary vein stenosis

Dislodgment of the coronary sinus lead was observed in a 79-year-old patient 8 months after implantation of a biventricular pacing system. A severe stenosis in the posterolateral branch, in which the lead was previously positioned, prohibited reinsertion of the lead. Because no other branches with adequate anatomy for lead insertion were available in the targeted area, the stenosis was dilated and stented. Subsequently, the left ventricular lead could be reimplanted in the same vessel.

Steroids prevent late extension of radiofrequency lesions in the thigh muscle of infant rats: implications for pediatric ablation

INTRODUCTION

Marked late enlargement of radiofrequency (RF) lesions may occur in immature myocardium, suggesting that late proarrhythmic effects may occur in infants and small children undergoing RF ablation. Because late lesion extension may be involved in this phenomenon, we evaluated the impact of corticosteroids on the healing of RF lesions created in the thigh muscle of 29 infant Wistar rats (30 days; 55 g).

METHODS

Lesion dimensions and histological characteristics were assessed acutely (n = 11), and at 30 days in controls (n = 11, 183 g) and rats (n = 7, 173 g) receiving hydrocortisone after ablation and betametasone for 29 days. Acute (n = 16) and chronic (30 days; n = 5) lesions were also evaluated in adult Wistar rats (300 g).

RESULTS

Acutely, lesions in adults and infants were well demarcated from the surrounding tissue. In adults, chronic lesions did not increase in size and were well demarcated histologically. Controls and treated infant rats did not differ with respect to the gross appearance of chronic lesions. Late lesions doubled in size (20 mm in diameter) and were poorly demarcated from the surrounding tissue, exhibiting multiple collagen strands extending from the lesion into normal muscular tissue. In the treatment group, healing was markedly delayed and the extent of collagen proliferation was significantly less than controls.

CONCLUSION

RF lesions created in the thigh muscle of infant rats reveal late enlargement and invasion of normal muscle by intense collagen proliferation. Steroids seem to limit late extension of RF lesions. These findings may have implications for RF ablation procedures in pediatric populations.

Coronary ischemia induced by radiofrequency ablation in the left atrium

INTRODUCTION

We report three cases of transient, reversible coronary ischemia occurring after radiofrequency ablation in the left atrium.

METHODS AND RESULTS

A 56-year-old man with a left atrial tachycardia that was mapped to the septum and roof of the atrium using a noncontact mapping developed 5-mm ST elevation in the anterolateral leads. Coronary angiography showed an occluded diagonal that was opened using intracoronary nitrate, which led to resolution of the ST changes. A 57-year-old man undergoing right upper pulmonary vein ablation developed 6-mm ST elevation in leads V1-V4, II, III, and aVF. Coronary angiography showed normal coronaries with slow flow into the left anterior descending artery, which resolved with nitrates. A 50-year-old man undergoing left lower pulmonary vein ablation developed 3-mm reversible inferior ST elevation. All patients were adequately anticoagulated after transseptal access to the left atrium.

CONCLUSION

Ablation in the left atrium, at the roof, septum, and left inferior wall, can cause transient coronary ischemia, possibly due to spasm, which can be reversed with intracoronary nitrates. This phenomenon has not been previously described.

Case report: pulmonary vein stenosis following RF ablation of paroxysmal atrial fibrillation: successful treatment with balloon dilation

Paroxysmal atrial fibrillation and atrial tachycardia may originate from a focal source in one or multiple pulmonary veins. A focal origin facilitates a potential cure amendable to radiofrequency ablation. Herein we report the case of a 16 year old adolescent male with a tachycardia induced cardiomyopathy who presented with very frequent paroxysmal episodes of atrial fibrillation, atrial flutter and atrial tachycardia. The origin of the arrhythmia was mapped to the secondary branches of the left lower pulmonary vein using an octapolar micro-mapping catheter. Immediately following application of three radiofrequency lesions, angiography of the left lower pulmonary vein revealed a region of focal stenosis at the site of energy application, with delayed pulmonary venous emptying. Attempts to relieve any element of spasm using direct administration of nitroglycerin were unsuccessful. Three months later repeat catheterization revealed an unchanged region of tight anatomical stenosis. Balloon dilation of two stenotic areas resulted in dramatic relief of the obstruction and improved venous drainage. Recatheterization 6 months later revealed mild restenosis that was successfully redilated. Intracardiac ultrasound demonstrated focal constriction. Care should be exercised in attempting RF ablation in distal arborization sites of the pulmonary veins in children, because of the small caliber compared to adult subjects. Radiofrequency induced focal areas of stenosis may be amenable to balloon catheter dilation.

Effects of intracardiac radiofrequency current application on coronary artery vessels in young pigs

INTRODUCTION

Radiofrequency current is widely used in children to ablate accessory AV pathways. Previous data in a pig model demonstrated coronary artery obstruction adjacent to radiofrequency current lesions 48 hours and 6 months after energy delivery. In the present study, the long-term effects (>6 months) of radiofrequency current application on coronary artery vessels in young pigs are assessed.

METHODS AND RESULTS

Radiofrequency current (500 kHz) was delivered over 30 seconds in ten piglets (mean body weight 12.8 kg) using a steerable 6-French catheter with a 4-mm thermistor tip electrode (target temperature 75 degrees C). Lesions were created under fluoroscopic and electrocardiographic guidance at the lateral right atrial (RA) wall above the tricuspid valve orifice, and at the lateral left atrial and left ventricular wall adjacent to the mitral valve orifice. Selective coronary angiography and intravascular ultrasound (IVUS) studies were performed 3, 6, 9, and 12 months after energy application. After 12 months, the lesions were studied pathohistologically. All lesions consisted of compact fibrous tissue. RA lesions extended to the adjacent right coronary artery and led to coronary artery involvement with increased fibrous tissue in the adventitia and media and intimal thickening in three animals. Coronary arterial narrowing was documented by IVUS during follow-up in all three cases 9 months after energy application. Angiography failed to demonstrate coronary pathology in any of the three animals.

CONCLUSION

The risk of late coronary artery lesions must be considered when catheter ablation at the RA wall is planned in children with free-wall accessory AV pathways.

Reduction of atrial fibrillation inducibility by radiofrequency ablation: an experimental study

A study is made of the antifibrillatory effects of radiofrequency (RF)-induced atrial lesions using nine Langendorff-perfused rabbit hearts in which the atrial electrophysiological properties and atrial fibrillation (AF) inducibility were modified by atrial stretching. Using a multiple electrode consisting of 121 unipolar electrodes, determinations were made of the atrial refractory periods, conduction velocity, wavelength of the atrial activation process, and the inducibility of sustained AF episodes (duration over 30 s) by atrial burst pacing in four situations: (a) control; (b) following dilatation of the right atrium; (c) after adding an RF linear lesion at the cava-tricuspid annulus isthmus; and (d) after adding two RF linear lesions rounding the base of the right atrial appendage and extending from the inferior zone of the sulcus terminalis to the anterior wall of the appendage. Under control conditions, AF was not induced in any of the experiments. The wavelengths were 10.5 +/- 1.2 cm for basic cycles of 250 ms and 6.6 +/- 0.5 cm for cycles of 100 ms. Following dilatation, a significant decrease was recorded in the atrial refractory periods, conduction velocity, and wavelength, which reached values of 6.1 +/- 0.7 cm (250-ms cycle, P < 0.01), and 3.9 +/- 0.3 cm (100-ms cycle, P < 0.01); AF was induced in five cases (P < 0.05). After producing the lesion at the cava-tricuspid isthmus, the electrophysiological modifications induced by atrial dilatation persisted (wavelength = 6.2 +/- 0.6 cm (250-ms cycle) and 4.3 +/- 0.3 cm (100-ms cycle); P < 0.01 vs the control) and AF was triggered in eight cases (P < 0.0001). In turn, on adding the two lesions at the right atrial free wall and appendage, AF was induced only in one experiment (P = NS vs control), and the dilatation-induced decrease in refractoriness and wavelength was attenuated. Nevertheless, differences remained significant with respect to the controls, with the exception of the functional refractory periods determined at cycles of 100 ms. In this phase, the wavelength was 6.6 +/- 0.7 cm (250-ms cycle, P < 0.01 vs control) and 4.9 +/- 0.5 cm (100-ms cycle; P < 0.05). Atrial conduction between the zones separated by the lesions was blocked at any frequency, or selectively at rapid atrial activation frequencies.

IN CONCLUSION

(a) the production of three linear lesions in the right atrium (cava-tricuspid isthmus, atrial appendage, and inferior free wall) reduces AF inducibility in the experimental model used; (b) conduction block (either absolute or frequency dependent) through the lesions, reduction in tissue mass caused by lesion creation, and possibly the attenuation of the shortening of atrial refractoriness and wavelength in the zones not separated by the lesions are implicated in the reduction of AF inducibility; and (c) the single lesion in the cava-tricuspid isthmus does not impede AF inducibility.

Prospective comparison of temperature guided microwave and radiofrequency catheter ablation in the swine heart

Microwave energy has been proposed as an alternative to radiofrequency energy for use during catheter ablation procedures. The purpose of this study was to prospectively compare, in an animal model, the lesion size associated with temperature guided catheter ablation using either microwave or radiofrequency energy. Eleven swine underwent catheter ablation with either radiofrequency (N = 4) or microwave energy (N = 7). In each animal catheter ablation was performed at 7-15 sites. At each site energy was delivered for 60 seconds using closed loop feedback temperature control to achieve a target temperature of 70 degrees C. Cardiac catheterization was performed before and after ablation. Animals were sacrificed approximately one month following the ablation procedure. Analysis of lesion size demonstrated that overall lesions created using radiofrequency energy were larger than those created using microwave energy. In the ventricle, lesions created using microwave energy were longer, but had a similar width and depth as those created using radiofrequency energy. An important relation was observed between the depth of lesions created using microwave energy and catheter stability, as evidenced by the temperature profile. Overall, lesions created using microwave energy are smaller than those created using radiofrequency energy. Catheter stability has an important impact on lesion size.

Coronary sinus stenosis as a late complication of catheter ablation in Wolff-Parkinson-White syndrome

This report describes a patient who developed stenosis of coronary sinus and cardiac veins five years after application of electric shock currents to the posterior mitral annulus and posteroseptal region of the tricuspid annulus for ablation of a left posterior accessory pathway and a right posteroseptal accessory pathway. This is the first angiographic documentation of coronary sinus stenosis as a late complication of electric ablation of accessory pathway.

Coronary artery involvement early and late after radiofrequency current application in young pigs

Radiofrequency current (500 kHz) was delivered by temperature guidance (75 degrees C) over a 30-second period in 10 young piglets with a steerable 6F electrode catheter equipped with a thermistor at the 4 mm tip electrode. Lesions were created at the right atrial aspect of the tricuspid valve anulus, at the left ventricular myocardium under the lateral mitral valve anulus, and at the left ventricular apex. After 48 hours, five animals were randomly sacrificed. Lesions in the five animals appeared as transmural gray-white coagulation necrosis. Lymphocytic infiltration around the right atrial lesions extended into the layers of the right coronary artery in four of five animals. After 6 months, lesions consisted of compact fibrous tissue in the remaining five animals. Right atrial lesions extended to the layers of the right coronary artery in four of five pigs. In two animals the lumen of the right coronary artery was narrowed because of intimal thickening by 25% and 40%, respectively. No increase in the lesion size was observed with the growth of the animals. Effects on the right coronary artery as a late sequela after radiofrequency current application may also be possible in human beings and should be considered when radiofrequency current ablation procedures are proposed in infants and young children.

Influence of radiofrequency catheter ablation on myocardial metabolism

We investigated the change of the arterial-coronary sinus lactate difference before and after radiofrequency ablation to assess the influence of radiofrequency ablation on myocardial metabolism. Sixteen patients underwent radiofrequency catheter ablation and blood sampling. The patients were further divided into two groups according to the energy received, group 1 (n = 8) with lower energy and group 2 (n = 8) with higher energy. The postpacing arterial-coronary sinus lactate difference was significantly higher than that 1 min after ablation (0.18 +/- 0.16 vs. -0.08 +/- 0.14 mmol/l, P < 0.01). The mean arterial-coronary sinus lactate difference obtained at 3 min, 5 min and 10 min increased gradually and finally approximated the postpacing lactate difference. The arterial-coronary sinus lactate difference 1 min after ablation of group 2 was significantly lower than that of group 1 (-0.03 +/- 0.14 vs. -0.13 +/- 0.14 mmol/l, P < 0.01). The arterial coronary sinus lactate differences of group 2 obtained at 3 min, 5 min and 10 min were also lower than those of group 1. However, the difference between the two groups decreased with time. This finding suggests that radiofrequency energy has an influence on the myocardial metabolism and higher energy causes more metabolic alteration than lower energy.

Direct angiography of the coronary sinus: impact on left posteroseptal accessory pathway ablation

The purpose of this study was to determine the incidence and types of venous branches and anomalies in posteroseptal accessory pathways (APs) and whether these findings are indicative for successful ablation sites. Some posteroseptal APs may be located epicardially, or may be associated with venous anomalies or related to the middle cardiac vein. These APs account for many of the failures encountered during endocardial ablation. Direct coronary sinus (CS) angiography was performed in 43 consecutive patients with left posteroseptal APs (n = 23) and in 20 patients with AV nodal reentrant tachycardia prior to catheter ablation. In 14 (61%) of 23 APs, a venous branch or an anomaly of the CS was found in the posteroseptal region (6 with middle cardiac vein, 2 with other ventricular venous branches, and 6 had a diverticulum). Eleven (48%) of 23 APs were successfully abolished from within that demonstrated venous system, with a median of four radiofrequency impulses. In the remaining 12 (52%) patients, ablation was attempted from the endocardial site of the mitral annulus. Repeat angiography after energy delivery revealed no major complications in any patient. One (5%) patient with AV nodal reentrant tachycardia had evidence of a CS anomaly (P < 0.01). Various types of venous branches and anomalies are associated with the majority of patients with left posteroseptal APs. The APs are directly related to these complex findings, and AP conduction can easily be eliminated from within the venous branches. CS angiography is suggested prior to catheter ablation of left posteroseptal APs to facilitate the ablation procedure.

Complications of diagnostic electrophysiologic studies and radiofrequency catheter ablation in patients with tachyarrhythmias: an eight-year survey of 3,966 consecutive procedures in a tertiary referral center

Predictors and comparisons of complications in patients with electrophysiologic study or radiofrequency ablation have not been assessed in previous published reports. The purpose of this study was to prospectively evaluate the procedure-specific complications and investigate the possible causes and predictors of complications in electrophysiologic study and radiofrequency ablation. Data of diagnostic electrophysiologic studies and radiofrequency ablation were prospective, and represented a consecutive series of 2,593 patients with 3,966 procedures. The present study showed that a significantly higher complication rate occurred in radiofrequency ablation than in electrophysiologic study (3.1% vs. 1.1%, respectively, p = 0.00002) and a significantly higher complication rate occurred in elderly than in young patients with electrophysiologic study (2.2% vs 0.5%, p = 0.0002) or radiofrequency ablation (6.1% vs 2.0%, p = 0.00015). Multiple logistic analysis found that older age (p < 0.01) and systemic disease in elderly patients (p < 0.01) were the independent predictors of complications in both procedures. Furthermore, there was no temporal trend in the incidence of complication. We conclude that the incidence of complication was higher in radiofrequency ablation, and elderly patients had a higher incidence of complications in both electrophysiologic study and radiofrequency ablation; these procedures, when performed by experienced personnel in an appropriately staffed and equipped laboratory, can be undertaken with an acceptable risk.

The evolution of platelet aggregability in patients undergoing catheter ablation for supraventricular tachycardia with radiofrequency energy: the role of antiplatelet therapy

Forty-two consecutive patients were checked for profiles of platelet aggregability before, during, and 10 and 30 minutes after catheter ablation. They were randomized into Group A (n = 20) who accepted intravenous aspirin (in 0.015 g/kg body weight) and Group P (n = 22) who accepted only placebo treatment. Blood samples were drawn from ascending aorta (Ao) and main pulmonary artery (MPA) simultaneously at each time period. In Group P, the EC50 of substrate induced platelet aggregability decreases significantly during (for ADP, from 1.72 to 0.78 mumol/L for samples from Ao, P < 0.0001; and from 1.68 to 0.69 mumol/L for MPA, P < 0.0001; for collagen, from 2.26 to 1.34 micrograms/mL for Ao, P < 0.005, and from 2.40 to 1.64 micrograms/mL, P < 0.0001) and 10 minutes after successful ablation (for ADP, to 0.70 mumol/L for Ao, P < 0.000, and to 0.61 mumol/L for MPA, P < 0.0001; for collagen, to 1.54 micrograms/mL for Ao, P < 0.01, and to 1.63 micrograms/mL, P < 0.0001), and then returned to baseline levels 30 minutes later (all P = NS) compared with comparative baseline levels. The levels of thromboxane B2 (TXB2) had the similar evolution. The evolution of platelet aggregability profiles was not associated with total energy dose, duration of energy application, duration of procedure, impedance, and ablation site. However, there were moderate positive correlations between the TXB2 levels and tip temperatures (r = 0.56, P < 0.05 for Ao and r = 0.65, P < 0.01 for MPA). These results suggest that increased platelet aggregability can occur during and 10 minutes after radiofrequency current ablation and antiplatelet therapy can maintain "flat" response of platelet aggregability to radiofrequency energy, which may provide possible benefits in preventing the occurrence of the complication.

Efficacy and safety of radiofrequency catheter ablation of left-sided accessory pathways through the coronary sinus

Radiofrequency catheter ablation of left-sided accessory pathways (APs) with the use of an endocardial technique carries all potential risks of left heart catheterization. We analyzed the determinants of success, efficacy, and safety of radiofrequency catheter ablation from the coronary sinus (CS), as a potential alternative to the endocardial technique in these patients. Thirteen patients (mean age 40 +/- 20 years) with 15 left-sided APs and a history of symptomatic supraventricular tachycardia were included in the study. Nine APs were localized in the left posteroseptal region, and the remaining 6 in the left free wall. Ablation from CS was attempted in 12 patients with 14 APs. In 1 patient ablation within the CS was not deemed safe because of a small venous lumen. All 14 APs were successfully ablated using either CS ablation alone or combined with the endocardial technique. Efficacy of the CS ablation as a primary technique was 56% (5 of 9 APs). In 5 additional APs, ablation in the CS eliminated pathway conduction after failed endocardial attempts. CS ablation either as a primary or a secondary technique eliminated conduction in 10 of 14 APs (71.4%) (group 1). In the remaining 4 APs (group 2), the primary CS attempt was unsuccessful and APs were ablated with a subsequent endocardial approach. Determinants of success for the CS method were local AP to atrial and/or ventricular electrogram amplitude ratios > or = 1 (p < 0.05). The success rate of CS ablation was 83% in the left posteroseptal APs adjoining the branching point of the middle cardiac vein or a CS anomaly.(ABSTRACT TRUNCATED AT 250 WORDS)

Feasibility of radiofrequency powered, thermal balloon ablation of atrioventricular bypass tracts via the coronary sinus: in vivo canine studies

Radiofrequency catheter ablation of left-sided accessory pathways is technically demanding and usually requires left heart catheterization. The feasibility of creating lesions from within the coronary sinus of sufficient size to ablate accessory pathways in humans using a thermal balloon catheter was studied in 20 dogs. In group 1 (n = 14), 17 thermal inflations were performed in 12 dogs at either 70 degrees, 80 degrees, or 90 degrees C each for 30 or 60 seconds (in 2 dogs two non-thermal control inflations were performed). Animals were sacrificed 6.3 +/- 1.6 days later. In group 2 (n = 6), seven thermal inflations were performed at 90 degrees C each for 180, 300, or 360 seconds. Group 2 animals received antiplatelet and anticoagulant therapy for 1 week and were sacrificed at 13 +/- 10.7 days. In both groups, hemodynamic, angiographic, and electrocardiographic studies were performed at baseline, 1 hour after inflation, and prior to sacrifice. All dogs remained clinically stable throughout the procedure and no complications were attributed to the effect of thermal inflation. Thermal lesions measured 14.4 +/- 4.4 mm in length and extended from the coronary sinus intima to a mean depth of 2.9 +/- 1.2 mm (range 1.4-6.5 mm). Group 2 lesions were significantly deeper than group 1 lesions (P = 0.03). Of the 24 thermal lesions created, atrial necrosis was present in 23 and ventricular necrosis in 11. In all lesions there was some degree of either atrial necrosis, ventricular necrosis, or both. A variable degree of coronary sinus thrombus was present in 18 dogs without clinical sequelae. It is concluded that radiofrequency balloon heating via the coronary sinus can create thermal lesions in the atrioventricular sulcus of dogs that may be of sufficient size to ablate accessory left-sided pathways in humans.

Histologic evolution of radiofrequency lesions in an old human myocardial infarct causing ventricular tachycardia

INTRODUCTION

Radiofrequency (RF) ablation of ventricular tachycardia (VT) late after myocardial infarction may be difficult due to characteristics of the infarct containing the reentry circuit. RF lesions in these infarcts in humans have not been characterized.

METHODS AND RESULTS

Catheter mapping and ablation of VT originating from an anterior wall infarct was performed 8 days and again 12 hours prior to death. Pacing identified a region of abnormal conduction where RF ablation terminated VT. This region contained strips of myocytes sandwiched between endocardial fibrosis and dense scar. RF lesions ranged from 2 x 2 mm to 5 x 10 mm and were up to 3 mm in depth. Acute lesions showed superficial thrombus and early coagulation necrosis without inflammation. Older lesions showed coagulation necrosis, sparse neutrophil infiltrate, minimal granulation tissue, hemorrhage, and mixed inflammatory infiltrate along the lumen without re-endothelialization.

CONCLUSION

In this patient, RF lesions had sufficient depth but not width to interrupt the thin, but potentially broad, sheets of myocytes in the reentry circuit. In thinned areas, RF lesions can extend to the epicardium. Selecting sites with abnormal electrograms confines RF lesions to the infarct region. Inflammation and hemorrhage could conceivably cause delayed effects of RF.

Catheter ablation of the accessory pathways of the Wolff-Parkinson-White syndrome and its variants

The basis of arrhythmias in the Wolff-Parkinson-White (WPW) syndrome and its variants is the presence of accessory atrioventricular connections. Those variants include the concealed form of the WPW syndrome, the permanent form of junctional reciprocating tachycardia, and Mahaim preexcitation. In all forms of symptomatic WPW syndrome, catheter ablation of the accessory atrioventricular connections using radiofrequency current has become the treatment of choice. This review traces the development of this therapy, outlines the basics of the technique, summarizes the results reported in the largest series, indicate remaining areas of controversy, and discusses the indications and limitations of radiofrequency ablation therapy.

Ultrastructural observations in the myocardium beyond the region of acute coagulation necrosis following radiofrequency catheter ablation

INTRODUCTION

We hypothesized that myocardial injury following radiofrequency (RF) catheter ablation may extend beyond the region of acute coagulation necrosis as defined by histochemical staining.

METHODS AND RESULTS

Five RF lesions were created in vivo in the left ventricle of two dogs using a 4-mm tipped ablation electrode in which RF power was adjusted to maintain an electrode-tissue interface temperature of 85 degrees C for 60 seconds. The lesions were bisected; one half of the lesions were stained with nitroblue tetrazolium (NBT) and the other half processed for electron microscopy. Three zones of interest were identified extending 0-3 mm, 3-6 mm, and > 6 mm from the visible pathologic lesion border. The degree of ultrastructural injury to the myocardium was scored for each zone. Electron microscopy demonstrated the presence of significant abnormalities of the plasma membrane, mitochondria, sarcomeres, sarcoplasmic reticulum, and gap junctions of myocytes, as well as damage to the microvasculature extending up to 6 mm beyond the pathologic lesion edge. The plasma membrane and gap junctions of myocytes and the microvasculature appeared particularly sensitive to thermal injury, whereas the intercalated discs were relatively thermally resistant.

CONCLUSION

RF catheter ablation results in ultrastructural damage to the myocardium extending up to 6 mm beyond the acute pathologic RF lesion border as defined by NBT histochemical staining.

Basic aspects of radiofrequency catheter ablation

Radiofrequency (RF) catheter ablation has become the treatment of choice for many symptomatic cardiac arrhythmias. It is presumed that the primary cause of tissue injury by RF ablation is thermally mediated, resulting in a relatively discrete homogeneous lesion. The mechanism by which RF current heats tissue is resistive heating of a narrow rim (< 1 mm) of tissue that is in direct contact with the ablation electrode. Deeper tissue heating occurs as a result of passive heat conduction from this small region of volume heating. Lesion size is proportional to the temperature at the electrode-tissue interface and the size of the ablation electrode. Temperatures above 50 degrees C are required for irreversible myocardial injury, but temperatures above 100 degrees C result in coagulum formation on the ablation electrode, a rapid rise in electrical impedance, and loss of effective tissue heating. Lesion formation is also dependent on optimal electrode-tissue contact and duration of RF delivery. Newer developments in RF ablation include temperature monitoring, longer ablation electrodes coupled to high-powered RF generators, and novel ablation electrode designs.

A finite element model for radiofrequency ablation of the myocardium

A finite element model was developed to simulate the temperature distributions produced by radiofrequency catheter ablation. This model incorporated blood, myocardium and torso tissues. The Laplace equation was solved to determine the steady-state electric field. The heat generation in the tissues was then computed from the power density distribution and the bioheat equation was solved to determine the time-varying temperature distribution, taking into account the convective energy exchange at the blood-myocardium and torso-air interfaces. This model was used to predict the lesion depth and to evaluate the effects of electrode location, changes of the electrical and thermal conductivities, and the electrode radius on the thermally induced damage to the myocardium. Temperature distributions induced by radiofrequency ablation were found to be: i) not very sensitive to the reference electrode location, ii) more sensitive to electrical conductivity changes than to thermal conductivity changes, and iii) larger electrodes allow a current distribution at higher level of power with reducing the chance of impedance rise.

Recognition and catheter ablation of subepicardial accessory pathways

OBJECTIVES

The purpose of this study was to characterize left-sided accessory pathways that traverse the atrioventricular (AV) groove subepicardially and to describe results of radiofrequency catheter ablation within the coronary sinus in the patients studied.

BACKGROUND

Radiofrequency catheter ablation has proved to be a safe and effective method for treatment of accessory pathways; however, subepicardial accessory pathways may account for some of the failures encountered during endocardial ablation.

METHODS

The study group comprised 51 consecutive patients with a left-sided accessory pathway who were undergoing radio-frequency catheter ablation. Initially, the ablation catheter was introduced into a femoral artery and positioned on the ventricular aspect of the mitral annulus. If this endocardial approach was unsuccessful, the ablation catheter was introduced into the coronary sinus and energy applied at sites with shorter activation times than those recorded from the endocardium.

RESULTS

Five (10%) of 51 patients with a left-sided accessory pathway could not have accessory pathway conduction interrupted with a median of 18 endocardial radiofrequency energy applications. Accessory pathway potentials were less frequent during endocardial mapping in these 5 patients than in the 46 patients whose accessory pathway was successfully ablated from the endocardial surface. All five of these patients later had successful ablation using one or two applications of radiofrequency energy from within the coronary sinus. Effective target site electrograms in the coronary sinus were characterized by an accessory pathway potential that was larger than the corresponding atrial or ventricular electrogram. There were no complications or recurrences after ablation within the coronary sinus.

CONCLUSIONS

Some left-sided accessory pathways may be difficult to ablate from the endocardial surface because they traverse the AV groove subepicardially. The absence of an accessory pathway potential during endocardial mapping in combination with a relatively large accessory pathway potential within the coronary sinus may be a useful marker of a subepicardial pathway. In this select group of patients, radiofrequency catheter ablation from within the coronary sinus appears to enhance efficacy.

Effect on coronary artery anatomy of radiofrequency catheter ablation of atrial insertion sites of accessory pathways

OBJECTIVES

The purpose of this study was to analyze the effects of radiofrequency catheter ablation of the atrial insertion site of accessory pathways on the angiographic appearance of coronary arteries.

BACKGROUND

Radiofrequency catheter ablation of accessory pathways requires the application of energy to the endocardial surface of the atrioventricular groove adjacent to the major epicardial coronary arteries. A systematic analysis of the effect of radiofrequency ablation on coronary arteries has not previously been demonstrated.

METHODS

Seventy consecutive patients with 76 accessory pathways (7 right free wall, 44 left free wall, 12 posteroseptal, 8 anteroseptal and 5 midseptal) were studied. Quantitative coronary angiography was performed before, immediately after and a mean of 69 +/- 42 days after radiofrequency catheter ablation.

RESULTS

Coronary artery diameter adjacent to the ablating electrode was 2.6 +/- 0.9 mm before ablation, 2.7 +/- 0.9 mm immediately after ablation and 2.7 +/- 1.0 mm at the time of follow-up study. Angiographic findings were unchanged from baseline in 69 of 70 patients immediately after ablation and in all 70 patients at the time of follow-up study.

CONCLUSIONS

Radiofrequency catheter ablation of the atrial insertion site of accessory pathways does not result in short-term angiographic changes in coronary artery anatomy.

Initiation of atrial fibrillation in the Wolff-Parkinson-White syndrome: the importance of the accessory pathway

Atrial fibrillation in the Wolff-Parkinson-White syndrome may be related to microreentry in the accessory pathway. If such is the case, catheter ablation of the accessory pathway should eliminate atrial fibrillation. Among 95 patients undergoing catheter ablation, 20 had atrial fibrillation during standard electrophysiologic study (atrial vulnerability) before ablation. There were 16 women and four men with a mean age of 32 years. Before ablation six patients required electrical cardioversion. Thirty minutes after ablation, 11 continued to have inducible atrial fibrillation. Atrial fibrillation terminated spontaneously in every patient after ablation. A control group of 20 patients with accessory pathway ablation had no inducible atrial fibrillation before or after ablation. Catheter ablation had no effect on atrial properties including functional refractory period (227 +/- 37 vs 215 +/- 29 msec before versus after ablation, mean +/- SD) or wavelength (7.4 +/- 3.2 vs 7.2 +/- 2.7 before versus after ablation). These data suggest that an intact accessory pathway is not necessary for initiation of atrial fibrillation in most patients with Wolff-Parkinson-White syndrome. A rapid ventricular response over the accessory pathway may facilitate the perpetuation of atrial fibrillation in persons prone to this arrhythmia.