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Handbook of Cardiac Anatomy, Physiology, and Devices pp 599–614Cite as

Cardiac Mapping Technology

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Abstract

In general, the methodologies for cardiac electrical mapping entail registration of the electrical activation sequences of the heart by recording extracellular electrograms. The initial use of cardiac mapping was primarily to better understand the normal electrical excitations of the heart. However, the focus in mapping over time has shifted to the study of mechanisms and substrates underlying various arrhythmias; these techniques have been employed to aid in the guidance of curative surgical and/or catheter ablation procedures. More recently, the advent and continued development of high-resolution mapping technologies have considerably enhanced our understanding of rapid, complex, and/or transient arrhythmias that typically cannot be sufficiently characterized with more conventional methodologies. For example, the ability to visualize endocardial structures during electrophysiology procedures has greatly advanced the understanding of complex cardiac arrhythmias in relation to their underlying anatomy. In addition, such technologies provide powerful tools in the subsequent treatment of cardiac patients, particularly with the promise of accurately pinpointing the source of arrhythmias and thereby providing possible curative treatments. This chapter will summarize the most recent developments in catheter navigation and three-dimensional arrhythmia mapping technologies including both intracardiac and noninvasive approaches.

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References

  1. Tawara S (1906) Das Reizleitungssystem des Säugetierherzens. Eine anatomisch-histologische studie über das atrioventrikularbündel und die Purkinjeschen fäden.

    Google Scholar 

  2. Mayer AG (1906) Rhythmical pulsation in scyphomedusae. Carnegie Institute of Washington, Washington, DC

    Book  Google Scholar 

  3. Mayer AG (1908) Rhythmical pulsation in scyphomedusae. In: II. Papers from the marine biological laboratory at Tortugas. Carnegie Institution, Washington DC, pp 115–131

    Google Scholar 

  4. Mines GR (1916) On dynamic equilibrium in the heart. J Physiol (Lond) 46:349–382

    Article  Google Scholar 

  5. Lewis T, Rothschild MA (1915) The excitatory process in the dog's heart, II: the ventricles. Philos Trans R Soc Lond B Biol Sci 206:181–266

    Article  Google Scholar 

  6. Lewis T, Feil S, Stroud WD (1920) Observations upon flutter and fibrillation. II The nature of auricular flutter. Heart 7:191–346

    Google Scholar 

  7. Barker PS, McLeod AG, Alexander J (1930) The excitatory process observed in the exposed human heart. Am Heart J 5:720–742

    Article  Google Scholar 

  8. Taccardi B (1962) Distribution of heart potentials on dog’s thoracic surface. Circ Res 11:862–869

    Article  CAS  PubMed  Google Scholar 

  9. Jackman WM, Wang XZ, Friday KJ et al (1991) Catheter ablation of accessory atrioventricular pathways (Wolff–Parkinson–White syndrome) by radiofrequency current. N Engl J Med 324:1605–1611

    Article  CAS  PubMed  Google Scholar 

  10. Gasparini M, Coltorti F, Mantica M, Galimberti P, Ceriotti C, Beatty G (2000) Noncontact system-guided simplified right atrial linear lesions using radiofrequency transcatheter ablation for treatment of refractory atrial fibrillation. Pacing Clin Electrophysiol 23:1843–1847

    Article  CAS  PubMed  Google Scholar 

  11. Schmitt H, Weber S, Tillmanns H, Waldecker B (2000) Diagnosis and ablation of atrial flutter using a high resolution, noncontact mapping system. Pacing Clin Electrophysiol 23:2057–2064

    Article  CAS  PubMed  Google Scholar 

  12. Schilling RJ, Davies DW, Peters NS (1998) Characteristics of sinus rhythm electrograms at sites of ablation of ventricular tachycardia relative to all other sites: a noncontact mapping study of the entire left ventricle. J Cardiovasc Electrophysiol 9:921–933

    Article  CAS  PubMed  Google Scholar 

  13. Sra J, Thomas JM (2001) New techniques for mapping cardiac arrhythmias. Indian Heart J 53:423–444

    CAS  PubMed  Google Scholar 

  14. Schumacher B, Jung W, Lewalter T, Wolpert C, Luderitz B (1999) Verification of linear lesions using a noncontact multielectrode array catheter versus conventional contact mapping techniques. J Cardiovasc Electrophysiol 10:791–798

    Article  CAS  PubMed  Google Scholar 

  15. Calkins H, Langberg J, Sousa J et al (1992) Radiofrequency catheter ablation of accessory atrioventricular connections in 250 patients. Abbreviated therapeutic approach to Wolff–Parkinson–White syndrome. Circulation 85:1337–1346

    Article  CAS  PubMed  Google Scholar 

  16. Wittkampf FH, Wever EF, Vos K et al (2000) Reduction of radiation exposure in the cardiac electrophysiology laboratory. Pacing Clin Electrophysiol 23:1638–1644

    Article  CAS  PubMed  Google Scholar 

  17. He B, Wu D (2001) Imaging and visualization of 3D cardiac electric activity. IEEE Trans Inf Tech Biomed 5:181–186

    Article  CAS  Google Scholar 

  18. Li G, He B (2001) Localization of the site of origin of cardiac activation by means of a heart-model-based electrocardiographic imaging approach. IEEE Trans Biomed Eng 48:660–669

    Article  CAS  PubMed  Google Scholar 

  19. He B, Li G, Zhang X (2002) Noninvasive three-dimensional activation time imaging of ventricular excitation by means of a heart-excitation model. Phys Med Biol 47:4063–4078

    Article  PubMed  Google Scholar 

  20. Liu Z, Liu C, He B (2006) Noninvasive reconstruction of three-dimensional ventricular activation sequence from the inverse solution of distributed equivalent current density. IEEE Trans Med Imaging 25:1307–1318

    Article  PubMed  Google Scholar 

  21. Han C, Pogwizd S, Killingsworth C, He B (2011) Noninvasive imaging of three-dimensional cardiac activation sequence in hearts with pacing and ventricular tachycardia: a quantitative comparison to intra-cardiac mapping on a rabbit model. Heart Rhythm 8:1266–1272

    Article  PubMed Central  PubMed  Google Scholar 

  22. Han C, Pogwizd S, Killingsworth C, He B (2012) Noninvasive reconstruction of three-dimensional ventricular activation sequence during pacing and ventricular tachycardia in the canine heart. Am J Physiol Heart Circ Physiol 302:H244–H252

    Article  CAS  PubMed Central  PubMed  Google Scholar 

  23. Han C, Pogwizd S, Killingsworth C, Zhou Z, He B (2013) Noninvasive cardiac activation imaging of ventricular arrhythmias during drug-induced QT prolongation in the rabbit heart. Heart Rhythm 10:1509–1515

    Article  PubMed Central  PubMed  Google Scholar 

  24. Han C, Pogwizd SM, Yu L, Zhou Z, Killingsworth C, He B (2015) Imaging cardiac activation sequence during ventricular tachycardia in a canine model of nonischemic heart failure. Am J Physiol Heart Circ Physiol 308:H108–H114. doi:10.1152/ajpheart.00196.201

    Article  CAS  PubMed  Google Scholar 

  25. Ben-Haim SA, Osadchy D, Schuster I (1996) Nonfluoroscopic, in vivo navigation and mapping technology. Nat Med 2:1393–1395

    Article  CAS  PubMed  Google Scholar 

  26. Gepstein L, Hayam G, Ben-Haim SA (1997) A novel method for nonfluoroscopic catheter-based electroanatomical mapping of the heart. In vitro and in vivo accuracy results. Circulation 95:1611–1622

    Article  CAS  PubMed  Google Scholar 

  27. Shpun S, Gepstein L, Hayam G, Ben-Haim SA (1997) Guidance of radiofrequency endocardial ablation with real-time three-dimensional magnetic navigation system. Circulation 96:2016–2021

    Article  CAS  PubMed  Google Scholar 

  28. Pappone C, Oreto G, Lamberti F et al (1999) Catheter ablation of paroxysmal atrial fibrillation using a 3D mapping system. Circulation 100:1203–1208

    Article  CAS  PubMed  Google Scholar 

  29. Poty H, Saoudi N, Abdel Aziz A, Nair M, Letac B (1995) Radiofrequency catheter ablation of type 1 atrial flutter. Prediction of late success by electrophysiological criteria. Circulation 92:1389–1392

    Article  CAS  PubMed  Google Scholar 

  30. Sra J, Bhatia A, Dhala A et al (2000) Electroanatomic mapping to identify breakthrough sites in recurrent typical human flutter. Pacing Clin Electrophysiol 23:1479–1492

    Article  CAS  PubMed  Google Scholar 

  31. Willems S, Weiss C, Ventura R et al (2000) Catheter ablation of atrial flutter guided by electroanatomic mapping (CARTO): a randomized comparison to the conventional approach. J Cardiovasc Electrophysiol 11:1223–1230

    Article  CAS  PubMed  Google Scholar 

  32. Shah DC, Jais P, Haissaguerre M et al (1997) Three-dimensional mapping of the common atrial flutter circuit in the right atrium. Circulation 96:3904–3912

    Article  CAS  PubMed  Google Scholar 

  33. Stevenson WG, Delacretaz E, Friedman PL, Ellison KE (1998) Identification and ablation of macroreentrant ventricular tachycardia with the CARTO electroanatomical mapping system. Pacing Clin Electrophysiol 21:1448–1456

    Article  CAS  PubMed  Google Scholar 

  34. Tomassoni G, Stanton M, Richey M, Leonelli FM, Beheiry S, Natale A (1999) Epicardial mapping and radiofrequency catheter ablation of ischemic ventricular tachycardia using a three-dimensional nonfluoroscopic mapping system. J Cardiovasc Electrophysiol 10:1643–1648

    Article  CAS  PubMed  Google Scholar 

  35. Kottkamp H, Hindricks G, Breithardt G, Borggrefe M (1997) Three-dimensional electromagnetic catheter technology: electroanatomic mapping of the right atrium and ablation of ectopic atrial tachycardia. J Cardiovasc Electrophysiol 8:1332–1337

    Article  CAS  PubMed  Google Scholar 

  36. Marchlinski F, Callans D, Gottlieb C, Rodriguez E, Coyne R, Kleinman D (1998) Magnetic electroanatomical mapping for ablation of focal atrial tachycardias. Pacing Clin Electrophysiol 21:1621–1635

    Article  CAS  PubMed  Google Scholar 

  37. Varanasi S, Dhala A, Blanck Z, Deshpande S, Akhtar M, Sra J (1999) Electroanatomic mapping for radiofrequency ablation of cardiac arrhythmias. J Cardiovasc Electrophysiol 10:538–544

    Article  CAS  PubMed  Google Scholar 

  38. Wittkampf FH, Wever EF, Derksen R et al (1999) LocaLisa: new technique for real-time 3Dimensional localization of regular intracardiac electrodes. Circulation 99:1312–1317

    Article  CAS  PubMed  Google Scholar 

  39. Avitall B, Helms RW, Kotov AV, Sieben W, Anderson J (1996) The use of temperature versus local depolarization amplitude to monitor atrial lesion maturation during the creation of linear lesions in both atria. Circulation 94:I-558

    Google Scholar 

  40. Borggrefe M, Budde T, Podczeck A, Breithardt G (1987) High frequency alternating current ablation of an accessory pathway in humans. J Am Coll Cardiol 10:576–582

    Article  CAS  PubMed  Google Scholar 

  41. Jenkins KJ, Walsh EP, Colan SD, Bergau DM, Saul JP, Lock JE (1993) Multipolar endocardial mapping of the right atrium during cardiac catheterization: description of a new technique. J Am Coll Cardiol 22:1105–1110

    Article  CAS  PubMed  Google Scholar 

  42. Eldar M, Ohad DG, Goldberger JJ et al (1997) Transcutaneous multielectrode basket catheter for endocardial mapping and ablation of ventricular tachycardia in the pig. Circulation 96:2430–2437

    Article  CAS  PubMed  Google Scholar 

  43. Triedman JK, Jenkins KJ, Colan SD, Van Praagh R, Lock JE, Walsh EP (1997) Multipolar endocardial mapping of the right heart using a basket catheter: acute and chronic animal studies. Pacing Clin Electrophysiol 20:51–59

    Article  CAS  PubMed  Google Scholar 

  44. Schalij MJ, van Rugge FP, Siezenga M, van der Velde ET (1998) Endocardial activation mapping of ventricular tachycardia in patients: first application of a 32-site bipolar mapping catheter electrode. Circulation 98:2168–2179

    Article  CAS  PubMed  Google Scholar 

  45. Triedman JK, Jenkins KJ, Colan SD, Saul JP, Walsh EP (1997) Intra-atrial reentrant tachycardia after palliation of congenital heart disease: characterization of multiple macroreentrant circuits using fluoroscopically based three-dimensional endocardial mapping. J Cardiovasc Electrophysiol 8:259–270

    Article  CAS  PubMed  Google Scholar 

  46. Greenspon AJ, Hsu SS, Datorre S (1997) Successful radiofrequency catheter ablation of sustained ventricular tachycardia postmyocardial infarction in man guided by a multielectrode “basket” catheter. J Cardiovasc Electrophysiol 8:565–570

    Article  CAS  PubMed  Google Scholar 

  47. Schmitt C, Zrenner B, Schneider M et al (1999) Clinical experience with a novel multielectrode basket catheter in right atrial tachycardias. Circulation 99:2414–2422

    Article  CAS  PubMed  Google Scholar 

  48. Nakagawa H, Ikeda A, Sharma T, Lazzara R, Jackman W (2012) Rapid high resolution electroanatomic mapping. Circ Arrhythm Electrophysiol 5:417–424

    Article  PubMed  Google Scholar 

  49. Ptaszek LM, Chalhoub F, Perna F et al (2013) Rapid acquisition of high-resolution electroanatomical maps using a novel multielectrode mapping system. J Interv Card Electrophysiol 36:233–242

    Article  PubMed  Google Scholar 

  50. Arshad A, Mittal S, Musat D et al (2013) Long-term success from FIRM ablation is maintained even if acute endpoint is not achieved. Heart Rhythm 10(P004-133)

    Google Scholar 

  51. Baykaner T, Clopton P, Lalani GG et al (2013) Targeted ablation at stable atrial fibrillation sources improves success over conventional ablation in high-risk patients: a substudy of the CONFIRM trial. Can J Cardiol 29:1218–1226

    Article  PubMed Central  PubMed  Google Scholar 

  52. Miller JM, Krummen DE, Narayan SM et al (2013) Multicenter validation of focal impulse and rotor modulation (FIRM) ablation for atrial fibrillation (CONFIRM-Multicenter Validation). AHA Scientific Sessions, November 2013, Oral presentation

    Google Scholar 

  53. Narayan SM, Krummen DE, Shivkumar K, Clopton P, Rappel WJ, Miller J (2012) Treatment of atrial fibrillation by the ablation of localized sources: the conventional ablation for atrial fibrillation with or without focal impulse and rotor modulation: CONFIRM trial. J Am Coll Cardiol 60:628–636

    Article  PubMed Central  PubMed  Google Scholar 

  54. Narayan SM, Krummen DE, Clopton P, Shivkumar K, Miller JM (2013) Direct ablation of coincidental elimination of stable rotors or focal sources may explain successful atrial fibrillation ablation: on-treatment analysis of the CONFIRM trial. J Am Coll Cardiol 60:138–147

    Article  Google Scholar 

  55. Schilling RJ, Peters NS, Davies DW (1998) Simultaneous endocardial mapping in the human left ventricle using a noncontact catheter: comparison of contact and reconstructed electrograms during sinus rhythm. Circulation 98:887–898

    Article  CAS  PubMed  Google Scholar 

  56. Schilling RJ, Peters NS, Davies DW (1999) Feasibility of a noncontact catheter for endocardial mapping of human ventricular tachycardia. Circulation 99:2543–2552

    Article  CAS  PubMed  Google Scholar 

  57. Taccardi B, Arisi G, Macchi E, Baruffi S, Spaggiari S (1987) A new intracavitary probe for detecting the site of origin of ectopic ventricular beats during one cardiac cycle. Circulation 75:272–281

    Article  CAS  PubMed  Google Scholar 

  58. Khoury DS, Taccardi B, Lux RL, Ershler PR, Rudy Y (1995) Reconstruction of endocardial potentials and activation sequences from intracavitary probe measurements. Localization of pacing sites and effects of myocardial structure. Circulation 91:845–863

    Article  CAS  PubMed  Google Scholar 

  59. Tuzcu V (2007) A nonfluoroscopic approach for electrophysiology and catheter ablation procedures using a three-dimensional navigation system. Pacing Clin Electrophysiol 30:519–525

    Article  PubMed  Google Scholar 

  60. Novak P, Macle L, Thibault B, Guerra P (2004) Enhanced left atrial mapping using digitally synchronized NavX three-dimensional nonfluoroscopic mapping and high-resolution computed tomographic imaging for catheter ablation of atrial fibrillation. Heart Rhythm 4:521–522

    Article  Google Scholar 

  61. Schilling RJ, Kadish AH, Peters NS, Goldberger J, Davies DW (2000) Endocardial mapping of atrial fibrillation in the human right atrium using a noncontact catheter. Eur Heart J 21:550–564

    Article  CAS  PubMed  Google Scholar 

  62. Schneider MA, Ndrepepa G, Zrenner B et al (2000) Noncontact mapping-guided catheter ablation of atrial fibrillation associated with left atrial ectopy. J Cardiovasc Electrophysiol 11:475–479

    Article  CAS  PubMed  Google Scholar 

  63. Liu TY, Tai CT, Chen SA (2002) Treatment of atrial fibrillation by catheter ablation of conduction gaps in the crista terminalis and cavotricuspid isthmus of the right atrium. J Cardiovasc Electrophysiol 13:1044–1046

    Article  PubMed  Google Scholar 

  64. Strickberger SA, Knight BP, Michaud GF, Pelosi F, Morady F (2000) Mapping and ablation of ventricular tachycardia guided by virtual electrograms using a noncontact, computerized mapping system. J Am Coll Cardiol 35:414–421

    Article  CAS  PubMed  Google Scholar 

  65. Kadish A, Hauck J, Pederson B, Beatty G, Gornick C (1999) Mapping of atrial activation with a noncontact, multielectrode catheter in dogs. Circulation 99:1906–1913

    Article  CAS  PubMed  Google Scholar 

  66. Barr RC, Spach MS (1978) Inverse calculation of QRS-T epicardial potentials from normal and ectopic beats in the dog. Circ Res 42:661–675

    Article  CAS  PubMed  Google Scholar 

  67. Ramanathan C, Raja NG, Jia P, Ryu K, Rudy Y (2004) Noninvasive electrocardiographic imaging for cardiac electrophysiology and arrhythmia. Nat Med 10:422–428

    Article  CAS  PubMed Central  PubMed  Google Scholar 

  68. Tilg B, Fischer G, Modre R et al (2002) Model-based imaging of cardiac electrical excitation in humans. IEEE Trans Med Imaging 21:1031–1039

    Article  PubMed  Google Scholar 

  69. He B, Li G, Zhang X (2003) Noninvasive imaging of ventricular transmembrane potentials within three-dimensional myocardium by means of a realistic geometry anisotropic heart model. IEEE Trans Biomed Eng 50:1190–1202

    Article  PubMed  Google Scholar 

  70. Zhang X, Ramachandra I, Liu Z, Muneer B, Pogwizd SM, He B (2005) Noninvasive three-dimensional electrocardiographic imaging of ventricular activation sequence. Am J Physiol Heart Circ Physiol 289:H2724–H2732

    Article  CAS  PubMed  Google Scholar 

  71. Liu C, Skadsberg N, Ahlberg S, Swingen C, Iaizzo P, He B (2008) Estimation of global ventricular activation sequences by noninvasive 3Dimensional electrical imaging: validation studies in a swine model during pacing. J Cardiovasc Electrophysiol 19:535–540

    Article  PubMed Central  PubMed  Google Scholar 

  72. Tikhonov AN, Arsenin VY (1977) The regularization method. In: Tikhonov AN, Arsenis VY (eds) Solutions of ill-posed problems. V.H. Winston & Sons, Washington, DC, pp 45–94

    Google Scholar 

  73. Rudy Y, Messinger-Rapport BJ (1988) The inverse problem in electrocardiography: solutions in terms of epicardial potentials. Crit Rev Biomed Eng 16:215–268

    CAS  PubMed  Google Scholar 

  74. Rudy Y, Oster HS (1992) The electrocardiographic inverse problem. Crit Rev Biomed Eng 20:25–45

    CAS  PubMed  Google Scholar 

  75. Rudy Y, Burnes JE (1999) Noninvasive electrocardiographic imaging. Ann Noninvasive Electrocardiol 4:340–358

    Article  Google Scholar 

  76. Ramanathan C, Rudy Y (2001) Electrocardiogaphic imaging. I. Effect of torso inhomogeneities on body surface electrocardiographic potentials. J Cardiovasc Electrophysiol 12:229–240

    Article  CAS  PubMed  Google Scholar 

  77. Ramanathan C, Rudy Y (2001) Electrocardiographic imaging. II. Effect of torso inhomogeneities on noninvasive reconstruction of epicardial potentials, electrograms, and isochrones. J Cardiovasc Electrophysiol 12:241–252

    Article  CAS  PubMed  Google Scholar 

  78. Ramanathan C, Jia P, Ghanem RN, Calvettie D, Rudy Y (2003) Noninvasive electrocardiographic imaging (ECGI): application of the generalized minimal residual method (GMRes). Ann Biomed Eng 31:981–994

    Google Scholar 

  79. http://www.cardioinsight.com/. Accessed 30 Dec 2014

    Google Scholar 

  80. Haissaguerre M, Hocini M, Shah AJ et al (2013) Noninvasive panoramic mapping of human atrial fibrillation mechanism: a feasibility report. J Cardiovasc Electrophysiol 24:711–717

    Article  PubMed  Google Scholar 

  81. Haissaguerre M, Hocini M, Denis A et al (2014) Driver domains in persistent atrial fibrillation. Circulation 130:530–538

    Article  PubMed  Google Scholar 

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Authors and Affiliations

  1. Medtronic, Inc., 8200 Coral Sea St. NE, Mailstop MVS46, Mounds View, Minneapolis, MN, 55112, USA

    Nicholas D. Skadsberg PhD & Timothy G. Laske PhD

  2. Department of Surgery, University of Minnesota, Minneapolis, MN, USA

    Nicholas D. Skadsberg PhD, Timothy G. Laske PhD & Paul A. Iaizzo PhD

  3. Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA

    Bin He PhD

  4. CardioInsight, Inc., Cleveland, OH, USA

    Charu Ramanathan PhD

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  1. Nicholas D. Skadsberg PhD
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  2. Bin He PhD
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  3. Timothy G. Laske PhD
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  4. Charu Ramanathan PhD
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  5. Paul A. Iaizzo PhD
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Correspondence to Nicholas D. Skadsberg PhD .

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  1. B172 Mayo, MMC 195, University of Minnesota Department of Surgery, Minneapolis, Minnesota, USA

    Paul A. Iaizzo

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Skadsberg, N.D., He, B., Laske, T.G., Ramanathan, C., Iaizzo, P.A. (2015). Cardiac Mapping Technology. In: Iaizzo, P. (eds) Handbook of Cardiac Anatomy, Physiology, and Devices. Springer, Cham. https://doi.org/10.1007/978-3-319-19464-6_32

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