Biomedical subjects

Gregory M Ayers

Publications and source records attributed to Gregory M Ayers.

8 recordsLinked to original sources

PubMed2003

Pulmonary vein isolation using transvenous catheter cryoablation for treatment of atrial fibrillation without risk of pulmonary vein stenosis.

OBJECTIVES: We sought to evaluate the efficacy and safety of pulmonary vein (PV) isolation using transvenous cryoablation for the treatment of atrial fibrillation (AF). BACKGROUND: Although electrical isolation of PVs with radiofrequency energy for the treatment of AF is feasible, it is associated with a significant risk of PV stenosis. Cryoablation is a new alternative therapy allowing ablation of tissue while preserving its underlying architecture. METHODS: In 52 patients with paroxysmal (n = 45) or persistent (n = 7) AF, PV isolation using the CryoCor cryoablation system (CyroCor Inc., San Diego, California) with a 10F deflectable transvenous catheter was performed as guided by ostial PV potentials. Cryoablation was applied twice at each targeted site (2.5 to 5 min/application). Computed tomography (CT) of the thorax was performed at baseline and at 3 and 12 months to evaluate for PV stenosis. RESULTS: All targeted PVs were completely isolated in 49 (94%) of 52 of patients. Of 152 PVs targeted, 147 (97%) were successfully isolated (mean 3.0 PVs isolated per patient). After a mean period of 12.4 +/- 5.5 months of follow-up, 37 (71%) of 52 patients had no recurrence of AF or were clinically improved, including 29 patients (56%) who had no recurrence of AF with (n = 11) or without the use of anti-arrhythmic drugs. At 3 and 12 months, the CT scan showed no evidence of PV stenosis associated with cryoablation in any patients. CONCLUSIONS: Transvenous catheter cryoablation is an effective method to create PV electrical isolation for the treatment of AF. A clinically satisfactory result can be achieved in 71% of patients with AF, without the risk of PV stenosis.

Adult↗

PubMed2003

Randomized study comparing radiofrequency ablation with cryoablation for the treatment of atrial flutter with emphasis on pain perception.

BACKGROUND: Radiofrequency ablation (RF) of atrial flutter (AFL) has a high procedural efficacy, a low recurrence rate, and reports of procedure-related pain. The aim of the present study was to compare RF with cryoablation (cryo) for the treatment of AFL, with emphasis on pain perception during application of energy. METHODS AND RESULTS: Fourteen patients (55+/-11 years, 11 males) with AFL were randomized to receive ablation of the cavotricuspid isthmus (CTI) by either RF or cryo. Cryothermia was delivered with the CryoCor Cryoablation System (10F, 6-mm tip), and radiofrequency energy was delivered with the use of an 8-mm-tip catheter. Pain was evaluated according to a visual analogue scale (VAS; 0 to 100). All patients in the cryo group were successfully ablated with a mean of 18 applications (9 sites), and RF was successful in 6 of 7 patients (not significant) with 13 applications (not significant). The mean temperature was -82 degrees C and 55 degrees C for cryo and RF, respectively. One patient in the cryo group perceived pain, versus all 7 patients in the RF group (P<0.05). The proportion of painful applications averaged 75.3% in the RF group and 2.0% in the cryo group (P<0.05), whereas the corresponding VAS for pain was 38.3+/-25.3 and 0.32+/-0.86, respectively (P<0.05). At 6-month follow-up, there were no recurrences of atrial flutter. CONCLUSION: Cryo, as compared with RF, produces significantly less pain during application. Although in the present study there was no significant difference in efficacy, larger studies will be needed to definitively compare efficacy.

Adult↗

PubMed2003

Dose-response relationship for successful internal atrial defibrillation.

The dose-response relationship for successful defibrillation has been determined in man for the ventricle but not for the atrium. The purpose of this study was to determine the dose-response relationship for internal atrial defibrillation in humans. Seventy-seven consecutive patients underwent internal atrial defibrillation for acute (n = 14) or chronic AF (n = 63). Shocks were delivered in 40-V increments between electrodes positioned in the coronary sinus and the right atrium until successful conversion or a maximum of 400 V was reached. The shock strength versus success of shock data were subjected to a Kaplan-Meier survival analysis combined with a nonparametric probability analysis to arrive at the dose-response relationship. Using this relationship, comparisons were made between acute and chronic AF and clinical relevant conversion percentages (20, 50, 80 and 95%) were estimated and were compared with the conventional mean threshold. There were significant dose-response relationships in both patients groups (P < 0.05). The Kaplan-Meier analysis comparing patients with chronic and acute AF showed significant differences in their dose-response relationships (P < 0.001). The estimated shock intensity for 95% conversion in patients with acute and chronic AF was 279 V (2.9 J) and 433 V (6.6 J), respectively (P < 0.001). The conventional mean defibrillation threshold in patients with acute (192 +/- 15 V. 1.4 +/- 0.2 J) and chronic AF (343 +/- 8 V, 4.4 +/- 0.2 J) predicted the 60% and 45% chance of successful conversion, respectively. In conclusion, this study demonstrates that single shock conversion data can be used to determine a dose-response relationship, which can be used to estimate the shock intensity required for specific successful atrial defibrillation efficacy and to compare different clinical factors that affect defibrillation efficacy.

Aged↗

PubMed2003

Rapid atrial pacing does not decrease the atrial defibrillation threshold.

The aim of the study was to evaluate the effect of preshock atrial pacing on the atrial defibrillation threshold (DFT) during internal cardioversion of AF. The implantable atrial defibrillator has been added to the therapeutic options for patients with recurrent episodes of persistent AF. Although the device is efficient in restoring sinus rhythm, patient discomfort is a limitation. Methods that lower the ADFT are needed. Eleven patients with AF underwent internal cardioversion. In a randomized, crossover design, ADFT testing was performed, applying a step-up protocol starting at 100 V. Rapid atrial pacing was performed with a right atrial catheter for 20 seconds at 90% of the average cycle length of the fibrillatory waves and was immediately followed by a biphasic defibrillation shock. At each energy level, pacing + shock was compared to shock only, until the level at which sinus rhythm was restored by both modes. The step-up protocol was thereafter repeated using the inverse sequence of the two modes. A total of 19 ADFTs were obtained. For 10 the ADFT was lower with pacing + shock, in 4 equal and in 5 higher, than with shock only. The ADFT (mean +/- SD) with pacing + shock was 260 +/- 84 V(3.4 +/- 2.9 J) and did not differ from shock only: 268 +/- 85 V(3.8 +/- 3.0 J) (P > 0.05). The coefficient of variation and the coefficient of reproducibility for pacing + shock was 16% and 60 V, respectively, and for shock only 17% and 61 V. Rapid atrial pacing did not influence the internal ADFT in AF. The randomized, crossover protocol used was reproducible between different modes, and seems useful when testing the impact of different interventions on the ADFT.

Atrial Fibrillation↗

PubMed2003

What characterizes episodes of atrial fibrillation requiring cardioversion? Experience from patients with an implantable atrial cardioverter.

BACKGROUND: Episodes of paroxysmal atrial fibrillation may cause disabling symptoms. Asymptomatic episodes of paroxysmal atrial fibrillation are, however, more common than symptomatic episodes. The aim of the study was to investigate whether episodes of atrial fibrillation for which the patient requires cardioversion differ from those in which the patient does not seek this therapy. METHODS: We studied 21 patients with atrial fibrillation treated with an implanted atrial cardioverter. The device displayed intracardiac electrograms from episodes of atrial fibrillation in which the patient received cardioversion and from episodes that did not lead to a hospital visit or cardioversion. The heart rate (mean, highest, and lowest) and the degree of ventricular interval irregularity were analyzed with these electrograms. RESULTS: There were 132 episodes of atrial fibrillation available for analysis, of which 73 led to cardioversion and 58 did not. Episodes leading to hospital/clinic visits and therapy had a higher maximum ventricular rate (130 vs 115/min, P =.0004) than episodes that did not cause the patients to seek therapy. This difference in heart rate was most prominent at the beginning of the episode, but tended to become more similar during the episode. There were no differences in ventricular cycle length irregularity between the 2 types of episodes. Moreover, treated episodes also had a significantly longer duration (mean duration 33 vs 9 hours, P =.002). CONCLUSIONS: Episodes of atrial fibrillation that cause the patient to seek cardioversion are characterized by a high initial ventricular rate and a longer duration than those that go untreated.

Adolescent↗

PubMed2002

Catheter-based cryoablation produces permanent bidirectional cavotricuspid isthmus conduction block in dogs.

INTRODUCTION: Catheter-based cryoablation has been shown to produce punctate and effective cardiac lesions to treat focal targets. However, sequential applications are required to produce a continuous linear lesion needed to cure macroreentrant arrhythmias with large critical isthmuses. The purpose of this study was to compare and contrast linear cardiac lesions produced with sequential applications using a novel cryoablation system to those produced using radiofrequency (RF) energy. METHODS AND RESULTS: Seven mongrel dogs were prepared for femoral venous insertion of the ablation catheter (either a 10-French, 6-mm tipped, bipolar cryoablation catheter (N = 5, cryo group) or a 7-French, 4-mm tipped, bipolar RF ablation catheter (N = 2, RF group)). Ablation of the cavotricuspid isthmus was performed by delivering applications at sequential locations across the isthmus. The cryo group received 6 to 10 (mean 8 +/- 1.4), 5-minute applications at 3 to 5 separate sites with a mean nadir temperature of -74.5 +/- 1.6 degrees C. Each dog in the RF group received 9, 90-second applications with a mean temperature and power of 62 +/- 0 degrees C and 32 +/- 3.6 W. No acute or chronic complications were associated with either form of ablation. Immediately and six weeks after the index procedure, electroanatomical mapping showed the presence of bidirectional isthmus conduction block in all dogs. Gross and histopathologic examination revealed the presence of linear lesions, which were continuous and transmural. CONCLUSION: Similar to RF ablation, catheter-based cryoablation can produce linear, transmural lesions in the cavotricuspid isthmus resulting in permanent bidirectional isthmus conduction block.

Animals↗

PubMed2002

Effect of coexisting cardiovascular disease on the long-term efficacy and safety of the implantable atrial defibrillator.

The long-term efficacy and safety of implantable atrial defibrillator (IAD) therapy in patients with AF and cardiovascular disease is unclear. The aim of this study was to evaluate the efficacy and safety of IAD therapy in patients with and without coexisting cardiovascular disease. In 115 patients implanted with an IAD, 85 patients had cardiovascular disease: 41 (48%) patients had 1 cardiovascular abnormality, 29 (35%) patients had 2, 13 (15%) patients had 3, and 2 (2%) patients had 4 different cardiovascular abnormalities. The device was programmed into a rhythm monitoring mode for the first 3-month postimplant period. All defibrillation therapy was performed under physician supervision to monitor safety and efficacy. After this initial monitoring period, patients were allowed to activate their device away from the hospital or clinic. A total of 357 spontaneous AF episodes occurred in 83 (72%) patients during observed operation and the mean shock efficacy was 93.5+/-20.3% (lower 95% confidence interval [CI] 89.8%). As of the lastfollow-up, 58 (55%) patients had transition to receive nonphysician observed therapy. Forty-two (72%) patients had experienced 332 episodes of AF for which theyhad received device therapy away from the hospital/clinic (mean shock efficacy 90.5+/-39.7%). The presence of hypertension, valvular heart disease, and ischemic heart disease did not affect the shock efficacy of the IAD during physician observed and nonobserved therapy (P > 0.05). However, the presence of congestive heart failure was associated with a lower clinical efficacy during observed and nonobserved therapy (P < 0.05). Overall, 5,262 shocks have been delivered with the IAD without any episode of proarrhythmia. The observed proarrhythmic risk was 0%, with an estimated maximum proarrhythmic risk of 0.06% per shock (95% upper CI). A stand-alone IAD appears to be safe in the presence of cardiovascular disease. The lower clinical efficacy for AF associated with congestive heart failure might be related to a higher rate of early reinitiation of AF after defibrillation.

Adult↗

PubMed2002

Acute results of transvenous cryoablation of supraventricular tachycardia (atrial fibrillation, atrial flutter, Wolff-Parkinson-White syndrome, atrioventricular nodal reentry tachycardia).

INTRODUCTION: Radiofrequency (RF) catheter ablation currently is used for treatment of cardiac arrhythmias. Although the success rate is high for almost all supraventricular tachycardias (SVT), this technique has some drawbacks, especially when pulmonary veins (PV) are targeted for treatment of atrial fibrillation (AF). Additionally, new techniques for isolation of the PVs have the drawback that they can be used only for PV isolation and not for routine treatment of other SVTs. The aim of this study was to report on the safety and efficacy of a new cryoablation system for treatment of all SVTs. METHODS AND RESULTS: Forty-nine patients with SVT (38 men; age 48 years, range 23-76) were enrolled in the study. Five patients were withdrawn from the study before they underwent cryoablation. The remaining 44 patients were treated with cryoablation (22 AF, 15 atrial flutter, 3 accessory pathway, 2 AV nodal reentrant tachycardia, 1 AV junction ablation for permanent AF, 1 atrial tachycardia). Cryoablation was performed with the CryoCor cryoablation system, which uses a precooling system and N2O as a refrigerant. The number of freezes applied varied according to the index arrhythmia treated. Successful isolation of PVs was performed in 20 of (96%) 21 AF patients and 53 of 55 veins. The overall acute success was 98% (43/44). Fifty-three PVs were isolated (2.5/patient). The success rate was 100% (23/23) for right-sided procedures. The average and nadir temperatures reached in right-sided and left-sided procedures were -77 degrees C and -80 degrees C and -75 degrees C and -78 degrees C, respectively. No acute PV stenosis was seen. CONCLUSION: This novel cryoablation system appears to be safe and can successfully treat different types of SVTs, including AF. Isolation of PVs is possible without producing stenosis. Despite the high blood flow in the right atrial isthmus and PVs, bidirectional conduction block can be achieved.

Adult↗