Dr. Anson Lee specializes in the surgical treatment of all heart diseases, including ischemic heart disease, structural heart disease, aortic disease, and arrhythmias. He has practiced cardiothoracic surgery at Stanford since 2015. Dr. Lee has a special interest in the surgical treatment of abnormal heart rhythms and minimally invasive techniques to treat heart disease.

Clinical Focus

  • Arrhythmia Surgery
  • Atrial Fibrillation
  • Arrhythmias, Cardiac
  • Maze procedure
  • Hybrid ablation
  • Aortic Aneurysm
  • Aortic Valve
  • Mitral Valve
  • Coronary Artery Bypass
  • minimally invasive surgery
  • Mitral Valve Repair
  • Valve Replacement Surgery
  • Heart Failure
  • Heart Transplantation
  • Lung Transplantation
  • Reoperative Cardiac Surgery
  • Transcatheter Aortic Valve Replacement
  • Thoracic and Cardiovascular Surgery

Academic Appointments

Professional Education

  • Board Certification: Thoracic and Cardiovascular Surgery, American Board of Thoracic Surgery (2016)
  • Fellowship:Washington University School of Medicine Cardiothoracic Training (2015) MO
  • Internship:Washington University (2006) MOUnited States of America
  • Residency:Washington University Barnes Jewish Hospital (2013) MO
  • Medical Education:Washington University School Of Medicine (2005) MO


2017-18 Courses


All Publications

  • Proteomic Profiling of Early Chronic Pulmonary Hypertension: Evidence for Both Adaptive and Maladaptive Pathology. Journal of pulmonary & respiratory medicine ; 5 (1)


    The molecular mechanisms governing right atrial (RA) and ventricular (RV) hypertrophy and failure in chronic pulmonary hypertension (CPH) remain unclear. The purpose of this investigation was to characterize RA and RV protein changes in CPH and determine their adaptive versus maladaptive role on hypertrophic development.Nine dogs underwent sternotomy and RA injection with 3 mg/kg dehydromonocrotaline (DMCT) to induce CPH (n=5) or sternotomy without DMCT (n=4). At 8-10 weeks, RA and RV proteomic analyses were completed after trypsinization of cut 2-D gel electrophoresis spots and peptide sequencing using mass spectrometry.In the RV, 13 protein spots were significantly altered with DMCT compared to Sham. Downregulated RV proteins included contractile elements: troponin T and C (-1.6 fold change), myosin regulatory light chain 2 (-1.9), cellular energetics modifier: fatty-acid binding protein (-1.5), and (3) ROS scavenger: superoxide dismutase 1 (-1.7). Conversely, beta-myosin heavy chain was upregulated (+1.7). In the RA, 22 proteins spots were altered including the following downregulated proteins contractile elements: tropomyosin 1 alpha chain (-1.9), cellular energetic proteins: ATP synthase (-1.5), fatty-acid binding protein (-2.5), and (3) polyubiquitin (-3.5). Crystallin alpha B (hypertrophy inhibitor) was upregulated in both the RV (+2.2) and RA (+2.6).In early stage hypertrophy there is adaptive upregulation of major RA and RV contractile substituents and attenuation of the hypertrophic response. However, there are multiple indices of maladaptive pathology including considerable cellular stress associated with aberrancy of actin machinery activity, decreased efficiency of energy utilization, and potentially decreased protein quality control.

    View details for DOI 10.4172/2161-105X.1000241

    View details for PubMedID 26246959

  • Acute Right Ventricular Failure After Successful Opening of Chronic Total Occlusion in Right Coronary Artery Caused by a Large Intramural Hematoma. Circulation. Cardiovascular interventions Kawana, M., Lee, A. M., Liang, D. H., Yeung, A. C. 2017; 10 (2)
  • Maze permutations during minimally invasive mitral valve surgery. Annals of cardiothoracic surgery Lee, A. M. 2015; 4 (5): 463-468


    Surgical ablation for atrial fibrillation is most frequently done in the concomitant setting, and most commonly with mitral valve surgery. Minimally invasive surgical techniques for the treatment of atrial fibrillation have developed contemporaneously with techniques for minimally invasive mitral valve surgery. As in traditional surgery for atrial fibrillation, there are many different permutations of ablations for the less invasive approaches. Lesion sets can vary from simple pulmonary vein isolation (PVI) to full bi-atrial lesions that completely reproduce the traditional cut-and-sew Cox Maze III procedure with variable efficacy in restoring sinus rhythm. Additionally, treatment of the atrial appendage can be done through minimally invasive approaches without any ablation at all in an attempt to mitigate the risk of stroke. Finally, hybrid procedures combining minimally invasive surgery and catheter-based ablation are being developed that might augment surgical treatment of atrial fibrillation at the time of minimally invasive mitral valve repair. These various permutations and their results are reviewed.

    View details for DOI 10.3978/j.issn.2225-319X.2015.09.07

    View details for PubMedID 26539352

  • Quantification of the functional consequences of atrial fibrillation and surgical ablation on the left atrium using cardiac magnetic resonance imaging EUROPEAN JOURNAL OF CARDIO-THORACIC SURGERY Robertson, J. O., Lee, A. M., Voeller, R. K., Damiano, M. S., Schuessler, R. B., Damiano, R. J. 2014; 46 (4): 720-728


    The effect of atrial fibrillation (AF) on left atrial (LA) function has not been well defined and has been largely based on limited echocardiographic evaluation. This study examined the effect of AF and a subsequent Cox-Maze IV (CMIV) procedure on atrial function.Cardiac magnetic resonance imaging (cMRI) was performed in 20 healthy volunteers, 8 patients with paroxysmal atrial fibrillation (PAF) and 7 patients with persistent or long-standing persistent atrial fibrillation (LSP AF). Six of the PAF patients underwent surgical ablation with the CMIV procedure and 5 underwent both pre- and postoperative cMRIs. The persistent or LSP AF patients underwent only postoperative cMRIs because all scans were performed with patients in normal sinus rhythm. Volume-time curves throughout the cardiac cycle and regional wall shortening were evaluated using the cine images and compared across groups.Compared with normal volunteers, patients with PAF had significantly decreased reservoir contribution to left ventricular (LV) filling (P = 0.0010), an increased conduit function contribution (P = 0.04) and preserved booster pump function (P = 0.14). Following the CMIV procedure, significant reductions were noted with respect to reservoir and booster pump function, with corresponding increases in conduit function. These differences were more drastic in patients with persistent/LSP AF. Regional wall motion was significantly reduced by PAF in all wall segments (P < 0.05), but was not further reduced by the CMIV. Despite changes in LA function, LV function was preserved following surgery.PAF significantly altered LA function and has a detrimental effect on regional wall motion. Surgical intervention further altered LA function, but the reasons for this are likely multifactorial and not entirely related to the lesion set itself.

    View details for DOI 10.1093/ejcts/ezt656

    View details for Web of Science ID 000344968500024

    View details for PubMedID 24523494

  • Importance of atrial surface area and refractory period in sustaining atrial fibrillation: Testing the critical mass hypothesis JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Lee, A. M., Aziz, A., Didesch, J., Clark, K. L., Schuessler, R. B., Damiano, R. J. 2013; 146 (3): 593-598


    The critical mass hypothesis for atrial fibrillation (AF) was proposed in 1914; however, there have been few studies defining the relationship between atrial surface area and AF. This study evaluated the effect of tissue area and effective refractory period (ERP) on the probability of sustaining AF in an in vivo model.Domestic pigs (n = 9) underwent median sternotomy. Epicardial activation maps were constructed from bipolar electrograms recorded from form-fitting electrode templates placed on the atria. Baseline ERPs were determined. ERP was lowered with a continuous infusion of acetylcholine (0.005-0.04 mg/Kg/min) until AF could be sustained after burst pacing. The atria were sequentially partitioned using bipolar radiofrequency ablation. ERPs were lowered using acetylcholine until AF could be sustained in each subdivision of atrial tissue. Each subdivision was further divided until AF was no longer inducible. At study completion, the heart was excised and the surface area of each section was measured.Over a range of ERPs from 75 to 250 ms, the probability of AF was correlated with increasing tissue area (range, 19.5-105 cm(2)) and decreasing ERP. Logistic regression analysis identified shorter ERP (P < .001) and larger area (P = .006) as factors predictive of an increased probability of sustained AF (area under the curve of the receiver-operator characteristic = 0.878).The probability of sustained AF was significantly associated with increasing tissue area and decreasing ERP. These data may lead to a greater understanding of the mechanism of AF and help to design better interventional procedures.

    View details for DOI 10.1016/j.jtcvs.2012.04.021

    View details for Web of Science ID 000323605800023

    View details for PubMedID 22995722

  • Differential calcium handling in two canine models of right ventricular pressure overload JOURNAL OF SURGICAL RESEARCH Moon, M. R., Aziz, A., Lee, A. M., Moon, C. J., Okada, S., Kanter, E. M., Yamada, K. A. 2012; 178 (2): 554-562


    The purpose of this investigation was to characterize differential right atrial (RA) and ventricular (RV) molecular changes in Ca(2+)-handling proteins consequent to RV pressure overload and hypertrophy in two common, yet distinct models of pulmonary hypertension: dehydromonocrotaline (DMCT) toxicity and pulmonary artery (PA) banding.A total of 18 dogs underwent sternotomy in four groups: (1) DMCT toxicity (n = 5), (2) mild PA banding over 10 wk to match the RV pressure rise with DMCT (n = 5); (3) progressive PA banding to generate severe RV overload (n = 4); and (4) sternotomy only (n = 4).In the right ventricle, with DMCT, there was no change in sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) or phospholamban (PLB), but we saw a trend toward down-regulation of phosphorylated PLB at serine-16 (p[Ser-16]PLB) (P = 0.07). Similarly, with mild PA banding, there was no change in SERCA or PLB, but p(Ser-16)PLB was down-regulated by 74% (P < 0.001). With severe PA banding, there was no change in PLB, but SERCA fell by 57% and p(Ser-16)PLB fell by 67% (P < 0.001). In the right atrium, with DMCT, there were no significant changes. With both mild and severe PA banding, p(Ser-16)PLB fell (P < 0.001), but SERCA and PLB did not change.Perturbations in Ca(2+)-handling proteins depend on the degree of RV pressure overload and the model used to mimic the RV effects of pulmonary hypertension. They are similar, but blunted, in the atrium compared with the ventricle.

    View details for DOI 10.1016/j.jss.2012.04.066

    View details for Web of Science ID 000311090700009

    View details for PubMedID 22632938

  • Congenital fistula from the left main coronary artery to the left atrium presenting with an acute myocardial infarction JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Anastacio, M. M., Lee, A. M., Lawton, J. S. 2012; 144 (6): E147-E148

    View details for DOI 10.1016/j.jtcvs.2012.09.015

    View details for Web of Science ID 000311086600002

    View details for PubMedID 23040318

  • Evaluation of a novel cryoablation system: in vivo testing in a chronic porcine model. Innovations (Philadelphia, Pa.) Weimar, T., Lee, A. M., Ray, S., Schuessler, R. B., Damiano, R. J. 2012; 7 (6): 410-416


    Cryoablation is commonly used at present in the surgical treatment of atrial fibrillation (AF). However, there have been few studies examining the efficacy of the commonly used ablation devices. This report compares the efficacy of two cryoprobes in creating transmural endocardial lesions on the beating heart in a porcine model for chronic AF.In six Hanford miniature swine, the right atrial appendage and the inferior vena cava were isolated using a bipolar radiofrequency clamp to create areas of known conduction block. A connecting ablation line was performed endocardially via a purse string with the novel malleable 10-cm Cryo1 probe for 2 minutes at -40°C. Additional ablation lines were created with the Cryo1 and the 3.5-cm 3011 Maze Linear probe on the right and the left atrial wall. Epicardial activation mapping was performed before and immediately after ablation as well as 14 days postoperatively. Histologic examination was performed 14 days postoperatively.Transmural lesions were confirmed in 83/84 cross-sections (99%) for the Cryo1 probe and in 40/41 cross-sections (98%) for the 3011 Maze Linear probe. There was no difference between the devices in lesion width (mean ± SD, Cryo1, 10.7 ± 3.5 mm; 3011, 10.0 ± 3.9 mm; P = 0.31), lesion depth (Cryo1, 4.5 ± 1.7 mm; 3011, 4.6 ± 1.5 mm; P = 0.74), or atrial wall thickness (Cryo1, 4.5 ± 1.8 mm; 3011, 4.7 ± 1.7 mm; P = 0.74). There was a conduction delay across the right atrial ablation line (20 ± 2 milliseconds vs 51 ± 8 milliseconds, P < 0.001) that remained unchanged at 14 days (51 ± 8 milliseconds vs 52 ± 10 milliseconds, P = 0.88).The Cryo1 probe created transmural lesions on the beating heart, resulting in sustained conduction delay. Both probes had a similar performance in lesion geometry in this chronic animal model.

    View details for DOI 10.1097/IMI.0b013e31828534e5

    View details for PubMedID 23422803

  • Evaluation of a novel cryoablation system: in vitro testing of heat capacity and freezing temperatures. Innovations (Philadelphia, Pa.) Weimar, T., Lee, A. M., Ray, S., Schuessler, R. B., Damiano, R. J. 2012; 7 (6): 403-409


    Cryoablation has been used to ablate cardiac tissue for decades and has been shown to be able to replace incisions in the surgical treatment of atrial fibrillation. This in vitro study evaluates the performance of a novel cryoprobe and compares it with existing commercially available devices.A new malleable 10-cm aluminum cryoprobe was compared with a rigid 3.5-cm copper linear probe using in vitro testing to evaluate performances under different thermal loads and with different tissue thicknesses. Radial dimensions of ice formation were measured in each water bath by a high-precision laser 2 minutes after the onset of cooling. Probe-surface temperatures were recorded by thermocouples. Tissue temperature was measured at depths of 4 mm and 5 mm from the probe-tissue interface. Time to reach a tissue temperature of -20°C was recorded.Ice formation increased significantly with lower water-bath temperatures (P < 0.001). Width and depth of ice formation were significantly less for the rigid linear probe (P < 0.012 and P < 0.001, respectively). There was no difference between the probes in the maximal negative temperature reached under different thermal loads or at different tissue depths. The malleable probe achieved significantly lower temperatures at the proximal compared with the distal end (-61.7°C vs -55.0°C, respectively; P < 0.001). A tissue temperature of -20°C was reached earlier at 4 mm than at 5 mm (P < 0.001) and was achieved significantly faster with the 3011 Maze Linear probe (P < 0.021).The new malleable probe achieved rapid freezing to clinically relevant levels in up to 5-mm-thick tissue. Both probes maintained their performance under a wide range of thermal loads.

    View details for DOI 10.1097/IMI.0b013e3182853e74

    View details for PubMedID 23422802

  • Chronic performance of a novel radiofrequency ablation device on the beating heart: Limitations of conduction delay to assess transmurality JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Lee, A. M., Aziz, A., Clark, K. L., Schuessler, R. B., Damiano, R. J. 2012; 144 (4): 859-865


    The creation of consistently transmural lesions with epicardial ablation on the beating heart has represented a significant challenge for current technology. This study examined the chronic performance of the AtriCure Coolrail device (AtriCure Inc, West Chester, Ohio), an internally cooled, bipolar radiofrequency ablation device designed for off-pump epicardial ablation. The study also examined the reliability of using acute intraoperative conduction delay to evaluate lesion integrity.Seven swine underwent median sternotomy. The right atrial appendage and inferior vena cava were isolated with a bipolar radiofrequency clamp. Linear ablation lines were created between these structures with the AtriCure Coolrail. Paced activation maps were recorded with epicardial patch electrodes acutely before and after ablation and after keeping the animals alive for 4 weeks. The conduction time across the linear ablation was calculated from these maps. The lesions were histologically evaluated with trichrome staining.Only 76% of cross-sections of Coolrail lesions were transmural, and only 1 of 12 ablation lines was transmural in every cross-section examined. Mapping data were available in 5 of the animals. Significant conduction delay was present after the creation of each line of ablation acutely; however, after 4 weeks, conduction time returned to preablation values, demonstrating lack of transmurality.The AtriCure Coolrail failed to reliably create transmural lesions. Although the Coolrail was able to create acute conduction delay, its failure to transmurally ablate the atrial myocardium left gaps along the length of the lesion, which resulted in neither chronic conduction block nor delay across any line of ablation.

    View details for DOI 10.1016/j.jtcvs.2012.01.001

    View details for Web of Science ID 000309111600020

    View details for PubMedID 22305553

  • Cardiac Surgery The Washington ManualTM of Surgery Lee, A., Damiano, Jr, R. edited by Aziz, A., Bharat, A., Fox, A., Porembka, M. Lippincott, Williams & Wilkins, Philadelphia. 2012; 6th: 695–722
  • Surgical ablation of atrial fibrillation Electrophysiological Disorders of the Heart Lee, A., Voeller , R., Damiano, Jr, R. edited by Saksena , S., Camm, A. Elsevier, Philadelphia. 2011; 2nd: 1415–1424
  • A minimally invasive cox-maze procedure: operative technique and results. Innovations (Philadelphia, Pa.) Lee, A. M., Clark, K., Bailey, M. S., Aziz, A., Schuessler, R. B., Damiano, R. J. 2010; 5 (4): 281-286


    The Cox-Maze procedure (CMP) for the surgical treatment of atrial fibrillation (AF) traditionally has required a median sternotomy and cardiopulmonary bypass. This study describes a method using ablation technologies to create the full Cox-Maze lesion set through a 5- to 6-cm right minithoracotomy.Twenty-two consecutive patients underwent a CMP through a right mini-thoracotomy and cardiopulmonary bypass. All patients were followed prospectively with electrocardiogram and 24-hour Holter monitoring at 3, 6, and 12 months. The CMP lesion set was created using bipolar radiofrequency energy and cryotherapy.There was no operative mortality or major complications.Two patients required a permanent pacemaker. Five patients (23%) had early atrial tachyarrhythmias. At last follow-up(mean, 18 ± 12 months), all the patients (n=22) were free from atrial dysrhythmias. At 3 months (n=19), 84% of patients were off antiarrhythmic drugs. At 6 months (n=18), 94% of patients were free from AF and off antiarrhythmic medications. At 12 months (n=16), 81% of patients were free from AF and off antiarrhythmic drugs and three patients remained on warfarin for a mechanical mitral valve.A full CMP can be performed through a right mini-thoracotomy with outstanding short-term results. This less invasive procedure can be offered to patients without compromising efficacy.

    View details for DOI 10.1097/IMI.0b013e3181ee3815

    View details for PubMedID 21057605

  • Vagal denervation and reinnervation after ablation of ganglionated plexi JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Sakamoto, S., Schuessler, R. B., Lee, A. M., Aziz, A., Lall, S. C., Damiano, R. J. 2010; 139 (2): 444-452


    Surgical ablation of ganglionated plexi has been proposed to increase efficacy of surgery for atrial fibrillation. This experimental canine study examined electrophysiologic attenuation and recovery of atrial vagal effects after ganglionated plexi ablation alone or with standard surgical lesion sets for atrial fibrillation.Dogs were divided into 3 groups: group 1 (n = 6) had focal ablation of the 4 major epicardial ganglionated plexi fat pads, group 2 (n = 6) had pulmonary vein isolation with ablation, and group 3 (n = 6) had posterior left atrial isolation with ablation. All fat pads were ablated. Sinus and atrioventricular interval changes during bilateral vagosympathetic trunk stimulation were examined before and both immediately and 4 weeks after ablation. Vagally induced effective refractory period changes and mean QRST area changes (index of local innervation) were examined in 5 atrial regions.Sinus and atrioventricular interval changes and heart rate variability decreased immediately after ablation, but only sinus interval changes were restored significantly after 4 weeks in all groups. Ablation-modified vagal effects on effective refractory period or QRST area changed heterogeneously in groups 1 and 2. In group 3, regional vagal effects were attenuated extensively postablation in both atria. Posterior left atrial isolation with ablation incrementally denervated the atria. In the long term, vagal stimulation increased QRST area changes relative to control values in all groups. Heart rate variability was also assessed.Ganglionated plexi ablation significantly reduced atrial vagal innervation. Restoration of vagal effects at 4 weeks suggests early atrial reinnervation.

    View details for DOI 10.1016/j.jtcvs.2009.04.056

    View details for Web of Science ID 000274014300026

    View details for PubMedID 19740492

  • Complications after Atrial Fibrillation Surgery Complications in Cardiothoracic Surgery: Avoidance and Treatment Lee, A., Damiano, Jr, R. edited by Little, A., Merrill , W. Wiley-Blackwell, London. 2010; 2nd: 404–418
  • Animal studies of epicardial atrial ablation HEART RHYTHM Schuessler, R. B., Lee, A. M., Melby, S. J., Voeller, R. K., Gaynor, S. L., Sakamoto, S., Damiano, R. J. 2009; 6 (12): S41-S45


    The Cox maze procedure is an effective treatment of atrial fibrillation, with a long-term freedom from recurrence greater than 90%. The original procedure was highly invasive and required cardiopulmonary bypass. Modifications of the procedure that eliminate the need for cardiopulmonary bypass have been proposed, including use of alternative energy sources to replace cut-and-sew lesions with lines of ablation made from the epicardium on the beating heart. This has been challenging because atrial wall muscle thickness is extremely variable, and the muscle can be covered with an epicardial layer of fat. Moreover, the circulating intracavitary blood acts as a potential heat sink, making transmural lesions difficult to obtain. In this report, we summarize the use of nine different unidirectional devices (four radiofrequency, two microwave, two lasers, one cryothermic) for creating continuous transmural lines of ablation from the atrial epicardium in a porcine model. We define a unidirectional device as one in which all the energy is applied by a single transducer on a single heart surface. The maximum penetration of any device was 8.3 mm. All devices except one, the AtriCure Isolator pen, failed to penetrate 2 mm in some nontransmural sections. Future development of unidirectional energy sources should be directed at increasing the maximum depth and the consistency of penetration.

    View details for DOI 10.1016/j.hrthm.2009.07.028

    View details for Web of Science ID 000276186900007

    View details for PubMedID 19959142

  • Evaluation of Revascularization Subtypes in Octogenarians Undergoing Coronary Artery Bypass Grafting CIRCULATION Aziz, A., Lee, A. M., Pasque, M. K., Lawton, J. S., Moazami, N., Damiano, R. J., Moon, M. R. 2009; 120 (11): S65-S69


    Recent data suggest that octogenarians' long-term survival after complete coronary artery bypass graft revascularization is superior to incomplete revascularization. Discriminating between variable definitions of "complete" complicates interpretation of survival data. We aimed to clarify octogenarian long-term survival rates by stratifying revascularization subtypes.From 1986 to 2007, 580 patients 80 to 94 years of age underwent coronary artery bypass graft. Functional complete revascularization was defined as at least 1 graft to all diseased coronary vessels with >50% stenosis. Traditional complete revascularization was defined as 1 graft to each major arterial system with at least 50% stenosis. Incomplete revascularization was defined as leaving diseased, ungrafted regions. Revascularization was functional in 279 (48%), traditional in 181 (31%), and incomplete in 120 (21%). Long-term survival was evaluated by Kaplan-Meier analysis. Of 537 operative survivors, there were 402 late deaths. Cumulative long-term survival totaled 2890 patient-years. Late survival (Kaplan-Meier) was similar between functional (mean, 6.8 years) and traditional (6.7 years) groups (P=0.51), but diminished with incomplete (4.2 years) revascularization (P=0.007). Survival by group at 5 years was: 59+/-3% functional, 57+/-4% traditional, and 45+/-5% incomplete. Survival at 8 years was: 40+/-3% functional, 37+/-4% traditional, and 26+/-5% incomplete. To minimize selection bias in patients with limited life expectancy, Kaplan-Meier analysis was repeated including only patients with survival >12 months. Survival was again impaired with incomplete revascularization (P=0.04), and there was no difference between functional and traditional complete revascularization (P=0.73).Bypassing all diseased arterial vessels after revascularization does not afford significant long-term survival advantage compared to a traditional approach. Incomplete revascularization, related to more extensive disease, is associated with an 18% decline in survival. These data suggest that it is important to avoid incomplete revascularization in octogenarians, but the supplementary endeavor required to perform functional complete revascularization does not improve survival.

    View details for DOI 10.1161/CIRCULATIONAHA.108.844316

    View details for Web of Science ID 000269773000010

    View details for PubMedID 19752388

  • Epicardial Ablation on the Beating Heart: Limited Efficacy of a Novel, Cooled Radiofrequency Ablation Device. Innovations (Philadelphia, Pa.) 2009; 4 (2): 86–92


    OBJECTIVE: To perform a minimally invasive procedure for atrial fibrillation without cardiopulmonary bypass, it is necessary to create transmural lesions on the beating heart. Although bipolar radiofrequency clamps can isolate the pulmonary veins, they have difficulty in performing any other left atrial lesions, particularly those of the traditional Cox-Maze procedure. This study examined the performance of an internally cooled, bipolar radiofrequency device designed for such an application. METHODS: Eleven domestic pigs underwent median sternotomy. Five animals had eight atrial lesions created with the radiofrequency device at times of 20, 30, 40, and 50 seconds. In six other pigs, the device was compared with another technology that has been used clinically for epicardial, beating heart ablation, the Guidant Flex 4 microwave device. The tissue was stained with 2,3,5-triphenyl-tetrazoluim chloride, and the lesions were sectioned at 5-mm intervals. Lesion width, depth, and transmurality were evaluated. RESULTS: The radiofrequency device had a linear dose-response relationship. Lesions were wider and deeper with increasing ablation times. A total of 40%, 45%, 60%, and 67% of lesions were transmural at times of 20, 30, 40, and 50 seconds, respectively. Ninety-one percent of lesions in tissue up to 4-mm thick were transmural after 50 seconds. However, performance in thicker tissue was poor. Lesions created by the device were deeper and more likely to be transmural than the Flex 4. CONCLUSIONS: This internally cooled, bipolar radiofrequency device can reliably create transmural lesions on tissue up to 4-mm thick and performs better than a microwave device.

    View details for DOI 10.1097/IMI.0b013e3181a348a2

    View details for PubMedID 22323899

  • The surgical treatment of atrial fibrillation Surg Clin North Am Lee, A., Melby , S., Damiano, Jr, R. 2009: 1001–1020, x-xi
  • Atrial fibrillation propagates through gaps in ablation lines: Implications for ablative treatment of atrial fibrillation HEART RHYTHM Melby, S. J., Lee, A. M., Zierer, A., Kaiser, S. P., Livhits, M. J., Boineau, J. P., Schuessler, R. B., Damiano, R. J. 2008; 5 (9): 1296-1301


    It has been hypothesized that atrial lesions must be transmural to successfully cure atrial fibrillation (AF). However, ablation lines often do not extend completely across the atrial wall.The purpose of this study was to determine the effect of residual gaps on conduction properties of atrial tissue.Canine right atria (n = 13) were isolated, perfused, and mounted on a 250-lead electrode plaque. The atria were divided with a bipolar radiofrequency ablation clamp, leaving a gap that was progressively narrowed. Conduction velocities at varying pacing rates and AF frequencies were measured before and after ablations. AF was induced with an extra stimulus and acetylcholine.Gap widths from 11.2 to 1.1 mm were examined. Conduction velocities through gaps were dependent cycle length (P = .002) and gap size (P <.001). Overall, 253 (97%) of a total of 260 gaps allowed paced propagation; 51 (91%) of 56 gaps 1-3 mm in width permitted paced propagation, as did 202 (99%) of 204 gaps >or=3.0 mm. Similarly, 253 (97%) of a total of 260 gaps allowed propagation of AF. For AF, 51 (93%) of 55 gaps 1-3 mm allowed AF to pass through, as did 202 (99%) of 205 gaps >or=3.0 mm. Gaps as small as 1.1 mm conducted paced and AF impulses.Conduction velocities were slowed through residual gaps. However, propagation of wave fronts during pacing and AF occurred through the majority of residual gaps, down to sizes as small as 1.1 mm. Leaving viable tissue in ablation lines for the treatment of AF could account for failures.

    View details for DOI 10.1016/j.hrthm.2008.06.009

    View details for Web of Science ID 000259281600013

    View details for PubMedID 18774106

  • Efficacy and safety of right and left atrial ablations on the beating heart with irrigated bipolar radiofrequency energy: A long-term animal study JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Melby, S. J., Gaynor, S. L., Lubahn, J. G., Lee, A. M., Rahgozar, P., Caruthers, S. D., Williams, T. A., Schuessler, R. B., Damiano, R. J. 2006; 132 (4): 853-860


    The Cox maze procedure is the most effective surgical treatment for atrial fibrillation; however, its complexity has limited its clinical utility. The purpose of this study was to simplify the procedure by using an irrigated bipolar radiofrequency ablation device on the beating heart without cardiopulmonary bypass.Six domestic pigs underwent median sternotomy. The pulmonary veins were circumferentially ablated. Electrical isolation was confirmed by pacing. Eight lesions were performed epicardially, and three lesions were performed through purse-string sutures with one of the jaws of the device introduced into the right atrium. After 30 days, magnetic resonance imaging was performed to assess atrial function, pulmonary vein anatomy, and coronary artery patency. Cholinergic stimulation and burst pacing were administered to induce atrial fibrillation. Histologic assessment of the heart was performed after the animal was killed.A modified Cox maze procedure was successfully performed with the irrigated bipolar radiofrequency device with no deaths. In every instance, the pulmonary veins were electrically isolated. Cholinergic stimulation with burst pacing failed to produce atrial fibrillation. Imaging studies revealed tricuspid regurgitation without evidence of pulmonary vein stenosis, coronary artery stenosis, or intra-atrial thrombus. Total atrial ejection fraction was 16.9% +/- 7.5%, a significant reduction. Histologically, 99% of the lesions were transmural, and there was no evidence of coronary sinus injury.Lesions on both the right and left atria can be created successfully on the beating heart with irrigated bipolar radiofrequency. The great majority of lesions with this device were transmural. This device should not be used on valvular tissue.

    View details for DOI 10.1016/j.jtcvs.2006.05.048

    View details for Web of Science ID 000240954600016

    View details for PubMedID 17000297

  • Microwave ablation for atrial fibrillation: Dose-response curves in the cardioplegia-arrested and beating heart ANNALS OF THORACIC SURGERY Gaynor, S. L., Byrd, G. D., Diodato, M. D., Ishii, Y., Lee, A. M., Prasad, S. M., Gopal, J., Schuessler, R. B., Damiano, R. J. 2006; 81 (1): 72-77


    Microwave ablation has been used to replace the traditional incisions used in the surgical treatment of atrial fibrillation. However, dose-response curves have not been established in surgically relevant models. The purpose of this study was to develop dose-response curves for the Flex 10 (Guidant, Inc) microwave device in both the acute cardioplegia-arrested heart and on the beating heart.Twelve domestic pigs (40 to 45 kg) were subjected to microwave ablation in either the arrested (n = 6) or beating heart (n = 6). The cardioplegia-arrested heart was maintained at 10 degrees to 15 degrees C while six atrial endocardial and seven right ventricular epicardial lesions were created in each animal. On the beating heart, six right atrial and seven ventricular epicardial lesions were created. Ablations were performed for 15, 30, 45, 60, 90, 120, and 150 seconds (65 W, 2.45 GHz). The tissue was stained with 2,3,5-triphenyl-tetrazolium chloride, and sectioned at 5-mm intervals. Lesion depth and width were determined from digital micrographs.Mean atrial wall thickness was 2.8 mm (range, 1 to 8 mm). In the arrested heart, 94% of atrial lesions were transmural at 45 seconds and 100% were transmural at 90 seconds. In the beating heart, only 20% of atrial lesions were transmural despite prolonged ablation times (90 seconds). Ventricular lesion width and depth increased with duration of application, and were similar on the arrested and beating hearts.Microwave ablation produces linear dose-response curves. Transmural lesions can be reliably produced on the arrested heart, but not consistently on the beating heart.

    View details for DOI 10.1016/j.athotacsur.2005.06.062

    View details for Web of Science ID 000234585400009

    View details for PubMedID 16368338

  • Dose response curves for microwave ablation in the cardioplegia-arrested porcine heart. heart surgery forum Gaynor, S. L., Byrd, G. D., Diodato, M. D., Ishii, Y., Lee, A. M., Prasad, S. M., Gopal, J., Berube, D., Schuessler, R. B., Damiano, R. J. 2005; 8 (5): E331-6


    Microwave ablation has been used clinically for the surgical treatment of atrial fibrillation, particularly during valve procedures. However, dose- response curves have not been established for this surgical environment. The purpose of this study was to examine dosimetry curves for the Flex 4 and Flex 10 microwave devices in an acute cardioplegia-arrested porcine model.Twelve domestic pigs (40-45 kg) were acutely subjected to Flex 4 (n = 6) and Flex 10 (n = 6) ablations. On a cardioplegically arrested heart maintained at 10-15(o)C, six endocardial atrial and seven epicardial ventricular lesions were created in each animal. Ablations were performed for 15 s, 30 s, 45 s, 60 s, 90 s, 120 s, and 150 s (65 W, 2.45 GHz). The tissue was stained with 2,3,5-triphenyl-tetrazolium chloride and lesions were sectioned at 5 mm intervals. Lesion depth and width were determined from digital photomicrographs of each lesion (resolution +/- .03 mm).Average atrial thickness was 2.88 +/- .4 mm (range 1.0 to 8.0 mm). 94% of ablated atrial sections created by the FLEX 4 (n = 16) and the FLEX 10 (n = 16) were transmural at 45 seconds. 100% of atrial sections were transmural at 90 seconds with the FLEX 10 (n = 14) and at 60 seconds with the Flex 4 device (n = 15). Lesion width and depth increased with duration of application.Both devices were capable of producing transmural lesions on the cardioplegically arrested heart at 65 W. These curves will allow surgeons to ensure transmural ablation by tailoring energy delivery to the specific atrial geometry.

    View details for PubMedID 16099735

  • Advances in surgical ablation devices for atrial fibrillation. New Arrhythmia Technologies Melby, S., Lee, A., Damiano, Jr, R. edited by Wang, P., Naccarelli , G., Rosen , M., Estes III , N., Hayes, D., Haines , D. Blackwell Publishing, Malden, Massachusetts. 2005: 233–241