Optical Mapping of the Human Atrioventricular Junction

Optical Mapping of the Human Atrioventricular Junction

William J. Hucker, PhD, Vadim V. Fedorov, PhD, Kelley V. Foyil, MS, Nader Moazami, MD, andIgor R. Efimov, PhDDepartment of Biomedical Engineering (W.J.H., V.V.F., K.V.F., I.R.E.) and Department of Surgery,School of Medicine (N.M.), Washington University, St. Louis, Mo

Fluorescent optical mapping of cardiac electrophysiology in animal models has produced awealth of information about the function of the cardiac pacemaking and conduction system.However, expanding optical mapping studies to the human conduction system willsignificantly increase our understanding of clinically relevant phenomena, such asatrioventricular nodal reentrant tachycardia, that are difficult to fully reproduce in animalmodels. In this report, we present the first instance of optical mapping data recorded from thehuman atrioventricular junction, revealing its dual pathway electrophysiology, which is thebasis of atrioventricular nodal reentrant tachycardia.

Explanted human hearts (n=2) were obtained at the time of cardiac transplantation and perfusedwith cardioplegic solution. The atrioventricular junction was cannulated, isolated from the restof the heart, immobilized with the excitation-contraction uncoupler blebbistatin (10 μmol/L),1 and optically mapped using the voltage sensitive dye Di-4-ANEPPS and a 16×16 photodiodearray. In the first heart, explanted because of idiopathic cardiomyopathy, successful perfusionof the His bundle and ventricular septum, but not the atrioventricular (AV) node, was achieved.In this preparation, a junctional rhythm of 55 bpm originated from the His bundle (Figure 1).Optical action potentials (OAPs) from the His displayed diastolic depolarization and a slowupstroke with the maximum derivative of the fluorescent signal dF/dtmax=2.8±0.5 U/s. Pacingthe surrounding working ventricular myocardium produced a sharper upstroke (dF/dtmax=37±11, P<0.001 versus His OAPs) and longer action potential duration (APD) than the His(APD80: 315±23 ms in His versus 410±3ms in ventricle, P<0.001). The activation map of theHis junctional rhythm demonstrated slow conduction (7 cm/s) transversely along the Hisbundle (Figure 1). These data provide the first optical recordings of the human His bundle.

In the second heart (with ischemic cardiomyopathy), the entire AV junction was perfused,enabling us to optically map AV nodal dual pathway characteristics for the first time in thehuman. We followed standard premature S1–S2 pacing protocols to unmask dual pathwayelectrophysiology: The S1–S2 interval was decreased until conduction block occurred in thefast pathway because of a long refractory period. The slow pathway then conducted the impulseto the His, as demonstrated by a longer interval between atrial and His activation. Previousrabbit studies demonstrated that slow- versus fast-pathway activation can be recognizedoptically2 and can be induced not only by premature stimuli but also by pacing the slow pathwaydirectly.3 We found that both methods of inducing slow-pathway conduction worked in thehuman.

Figure 2A illustrates atrial pacing at 60 bpm, which depolarized the endocardial atrial layerwith conduction velocities ranging from 30 cm/s to 60 cm/s (atrial APD80: 390±22 ms). After

Correspondence to Igor R. Efimov, Washington University in St. Louis, Department of Biomedical Engineering, Campus Box 1097, 1Brookings Dr, St. Louis, MO 63130. E-mail [email protected]: None.

NIH Public AccessAuthor ManuscriptCirculation. Author manuscript; available in PMC 2009 September 16.

Published in final edited form as:Circulation. 2008 March 18; 117(11): 1474–1477. doi:10.1161/CIRCULATIONAHA.107.733147.

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the AV nodal delay, His activation, seen in the optical recordings as a double-humped OAP,occurred at 126 ms.4 Activation between 33 ms and 114 ms was difficult to recognize in thefluorescent signals. However, nodal components of OAP upstrokes could be seen in sometraces (Figure 2). Moving the pacing electrode ∼1-mm closer to the AV groove (still pacing at60 bpm) produced conduction consistent with slow-pathway activation (Figure 2B). The pacingstimulus activated the atrial myocardium as before. However, His depolarization now occurredat 206 ms, and double-humped OAPs began slightly inferior and anterior to those in Figure2A. Once the His was activated, longitudinal conduction was rapid (80 cm/s). S1–S2 intervalsof 600 ms to 550 ms produced the same slow-pathway conduction seen in Figure 2B, and S1–S2 intervals of 530 ms to 510 ms induced an extra beat consistent with typical slow-fast AVnodal reentry (Figure 3). His electrogram morphology and amplitude also changed with thechange in activating pathway (compare Figure 2A to 2B and Figures 3 to 4) as shown previouslyin rabbits.3

Histology of the second heart is shown in Figure 4 at the locations indicated in Figures 2 and3. Activation of the large inferior nodal extension in this heart (Figure 4A), which is the possiblesubstrate of the slow pathway, was difficult to recognize (perhaps because of its depth in thetissue).

AcknowledgmentsSources of Funding: Dr Efimov is supported by American Heart Association grant-in-aid 0750031Z.

References1. Fedorov VV, Lozinsky IT, Sosunov EA, Anyukhovsky EP, Rosen MR, Balke CW, Efimov IR.

Application of blebbistatin as an excitation-contraction uncoupler for electrophysiologic study of ratand rabbit hearts. Heart Rhythm 2007;4:619–626. [PubMed: 17467631]

2. Nikolski V, Efimov I. Fluorescent imaging of a dual-pathway atrioventricular-nodal conductionsystem. Circ Res 2001;88:E23–E30. [PubMed: 11179207]

3. Hucker WJ, Sharma V, Nikolski VP, Efimov IR. Atrioventricular conduction with and without AVnodal delay: two pathways to the bundle of His in the rabbit heart. Am J Physiol Heart Circ Physiol2007;293:H1122–H1130. [PubMed: 17496219]

4. Efimov IR, Mazgalev TN. High-resolution, three-dimensional fluorescent imaging reveals multilayerconduction pattern in the atrioventricular node. Circulation 1998;98:54–57. [PubMed: 9665060]

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Circulation. Author manuscript; available in PMC 2009 September 16.

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Figure 1.Junctional rhythm in the His bundle with schematic of the atrioventricular junction shown inthe right inset for orientation. Spontaneous activity began in the superior region of the Hisbundle and spread transversely at 7 cm/s. OAPs recorded from the His are shown in the leftinset, and the bold His OAP in the inset is shown at a higher magnification on the right. Becausethe ventricular septum (VS) was cut to isolate the AV junction, the septal myocardium waselectrically uncoupled from the His bundle. Therefore, pacing the ventricular septum producedactivity that was completely independent from His activity. Ventricular OAPs had a longeraction potential duration and faster upstroke than His potentials. His potentials displayeddiastolic depolarization (compare the baseline of the His signal to that of the ventricular signal).Photodiode resolution was 0.5×0.5 mm. AVN indicates atrioventricular node; CS, coronarysinus; FOV, field of view; IAS, interatrial septum; INE, inferior nodal extension; RAO, rightanterior oblique; TV, tricuspid valve; S, superior; I, inferior; P, posterior; and A, anterior.



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Figure 2.Optical action potentials recorded from the AV junction were composed of multiplecomponents. Pacing the atrial myocardium produced a fast wave of excitation that spread acrossthe interatrial septum (IAS) (gray activation maps) that was responsible for the initial atrialupstroke (A) of the OAPs shown. His activation produced an additional hump in OAPs recordednear the His bundle (OAP 4), and the colored activation maps were constructed from the Hiscomponent of these OAPs. The bipolar His electrogram (EGM) indicates His activation at 126ms in panel A, and at 206 ms in panel B, which verifies that these OAP components reflectHis activation. The bipolar His EGM is much larger in panel A than in panel B (same scale).The changes in His activation time and His EGM amplitude from panel A to panel B suggestthat panel A was fast-pathway conduction and panel B was slow-pathway conduction. SomeOAPs (such as OAP 3) contained a small change in upstroke following the atrial upstroke butpreceding the His component, reflecting AV nodal conduction (N). OAPs recorded near theINE did not reflect any obvious component indicating INE activation (OAP 2). The locationsof the histology slides shown in Figure 4 are indicated. The field of view (FOV) of panel B isshifted slightly from panel A, as indicated in the schematic inset. Pacing occurred at time zeroat the location marked by square pulse. Photodiode resolution was 2×2 mm. FP indicates fastpathway input of the AVN; SP, slow-pathway input of the AVN. Other abbreviations as inFigure 1.



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Figure 3.After pacing with an S1 cycle length of 1000 ms (60 bpm), a premature S2 stimulus at 510 msproduced an extra beat consistent with slow AVN reentry. Field of view (FOV) is the same asFigure 2A. The S2 stimulus excited the atrium but failed to conduct to the His (see His EGM).However an extra beat followed 440 ms after the S2, originating from the approximate locationof the fast pathway (FP) input to the AVN. The extra beat spread across the atrium in theopposite direction of the S2 with its latest atrial activation near the INE. After a 260-ms delay,His activation occurred, shown in the colored activation map and seen in the His EGM as amuch smaller signal than that recorded during the S1 beat. Gray arrows mark the proposedcircuit of reentry; however, slow-pathway conduction after the S2 atrial excitation was not



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readily apparent in the fluorescent optical traces. Therefore, the jagged gray arrow on the S2map marks the presumed location of the slow pathway. Photodiode resolution was 2×2 mm.Abbreviations as in Figures 1 and 2.



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Figure 4.Masson Trichrome staining of sections taken throughout the AV junction, corresponding tothe locations of photodiodes 2 to 4 in Figures 2 and 3. A, The INE is covered on its endocardialaspect by fibro-fatty tissue and a very thin layer of atrial myocardium, which contributed tothe atrial component of the OAPs recorded from this region. OAPs recorded during slow-pathway conduction did not reflect any obvious INE component. B, The AVN is also coveredwith a layer of fibro-fatty tissue and atrial myocardium above its endocardial aspect, whichwas responsible for the initial upstroke seen in the OAPs recorded above the AVN. C, The Hisbundle is surrounded by the fibrous tissue of the central fibrous body (CFB). The tricuspidvalve (TV) was cut during the experiment to facilitate optical mapping of the His bundle. TheHis electrode location is indicated as 2 dots reflecting the actual size of the bipolar wires ofthe electrode. The inset shows the change in His EGM amplitude that occurred with a prematurestimulus. OAPs recorded from this region possessed both atrial and His components, yet onlyHis and fibrous tissue are present, implying that the atrial component of the OAPs originatedfrom light scattering through the translucent connective tissue of the CFB. IAS indicatesinteratrial septum; VS, ventricular septum.



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Optical Mapping of the Human Atrioventricular Junction