A computerized method for the rapid display of ventricular activation during the intraoperative study of arrhythmias

[History of surgical treatment of cardiac arrhythmias in Germany : Surgical treatment of ventricular tachycardia and supraventricular tachycardia, especially pre-excitation syndromes (WPW)]

The history of surgical treatment of ventricular tachycardias (VT) is short, lasting from 1978 until 1993. "Indirect procedures" with infarct scar resection were performed without electrophysiologic studies, whereas "direct procedures" consisted of either complete endocardial incisions ("encircling endocardial ventriculotomy") or large endocardial resections ("endocardial peel-off" technique) after precise epicardial and endocardial mapping procedures. In Germany, the first to report on intra-operative electrophysiologic mapping for VT treatment were Ostermeyer, Breithardt and Seipel in 1979. In 1981, the Hannover group (Frank, Klein) published their first results of surgical treatment of VT. In 1984, Ostermeyer et al. demonstrated that a partial endocardial incision resulted in more beneficial results with less myocardial damage (8% versus 46%) than applying a complete encircling incision. In 1987, the Düsseldorf group reported treatment results of 93 patients. After 5 years, 77% had no VT recurrence, while total mortality after 1 year was 11% and after 5 years 30%. In 1992, the Hannover group reported results of 147 patients after endocardial resection for VT. Total mortality after 3 years was 27%; recurrence of VT events occurred in 18% of the surviving cohort.The history of surgical procedures for supraventricular tachycardia (SVT), in particular Wolff-Parkinson-White (WPW) syndrome, is even shorter than that of surgery for VT. As early as 1969, Sealy, Gallagher and Cox reported the first cases of surgical intervention for WPW syndrome via endocardial access in cardioplegic arrest. In 1984, Guiraudon and Klein reported on a new procedure with epicardial access to the accessory bundle without cardioplegia in laterally localised conduction pathways. In Germany, too, the groups in Düsseldorf (Ostermeyer, Seipel, Breithardt, Borggrefe) from 1980 and the Hannover group (Frank, Klein and Kallfelz) from 1981 performed surgical procedures for WPW syndrome. In 1987, Borggrefe reported on 18 patients with WPW syndrome and atrial fibrillation who had undergone surgery. After 2 years, 14 of 18 patients had no recurrences of tachycardia; in 1989, Frank, Klein and Kallfelz (Hannover) reported on 10 children (2-14 years) operated on using the cryoablation technique. Between 1984 and 1992, a total of 120 patients with SVT, mostly WPW syndrome, were operated on in Hannover; after 42 months, 12 patients had a recurrence of SVT. Two patients died during the reoperation.

Ventricular fibrillation: how do we put the genie back in the bottle?

I am deeply grateful and honored to receive the 2006 Distinguished Scientist Award from the Heart Rhythm Society. Many outstanding individuals have received this award since it was established in 1982, and it is humbling to realize that my small feet are walking in the footsteps of these giants. I would be remiss if I did not thank the numerous colleagues, fellows, and students who performed most of the work leading to the papers of which I am a coauthor.

Ventricular fibrillation: mechanisms of initiation and maintenance

Ventricular fibrillation (VF) is the major immediate cause of sudden cardiac death. Traditionally, VF has been defined as turbulent cardiac electrical activity, which implies a large amount of irregularity in the electrical waves that underlie ventricular excitation. During VF, the heart rate is too high (> 550 excitations/minute) to allow adequate pumping of blood. In the electrocardiogram (ECG), ventricular complexes that are ever-changing in frequency, contour, and amplitude characterize VF. This article reviews prevailing theories for the initiation and maintenance of VF, as well as its spatio-temporal organization. Particular attention is given to recent experiments and computer simulations suggesting that VF may be explained in terms of highly periodic three-dimensional rotors that activate the ventricles at exceedingly high frequency. Such rotors may show at least two different behaviors: (a) At one extreme, they may drift throughout the heart at high speeds producing beat-to-beat changes in the activation sequence. (b) At the other extreme, rotors may be relatively stationary, activating the ventricles at such high frequencies that the wave fronts emanating from them breakup at varying distances, resulting in complex spatio-temporal patterns of fibrillatory conduction. In either case, the recorded ECG patterns are indistinguishable from VF. The data discussed have paved the way for a better understanding of the mechanisms of VF in the normal, as well as the diseased, human heart.

Self-organization and the dynamical nature of ventricular fibrillation

This article reviews recent data supporting the conjecture that, in the structurally and electrophysiologically normal heart, cardiac fibrillation is not a totally random phenomenon. Experimental and numerical studies based on the theory of excitable media suggest that fibrillation in the mammalian ventricles is the result of self-organized three-dimensional (3-D) electrical rotors giving rise to scroll waves that move continuously (i.e., drift) throughout the heart at varying speeds. A brief review of studies on the dynamics of rotors in two-dimensional (2-D) and 3-D excitable media is presented with emphasis on the experimental demonstration of such dynamics in cardiac muscle of various species. The discussion is centered on rotor dynamics in the presence and the absence of structural heterogeneities, and in the phenomena of drifting and anchoring, which in the electrocardiogram (ECG) may manifest as life-threatening cardiac rhythm disturbances. For instance, in the rabbit heart, a single electrical rotor that drifts rapidly throughout the ventricles gives rise to complex patterns of excitation. In the ECG such patterns are indistinguishable from ventricular fibrillation. On the other hand, a rotor that anchors to a discontinuity or defect in the muscle (e.g., a scar, a large artery or a bundle of connective tissue) may result in stationary rotating activity, which in the ECG is manifested as a form of so-called "monomorphic" ventricular tachycardia. More recent data show that ventricular fibrillation occurs in mammals irrespective of size or species. While in small hearts, such as those of mice and rabbits, a single drifting or meandering rotor can result in fibrillation, in larger hearts, such as the sheep and possibly the human, fibrillation occurs in the form of a relatively small number of coexisting but short-lived rotors. Overall, the work discussed here has paved the way for a better understanding of the mechanisms of fibrillation in the normal, as well as diseased human heart. (c) 1998 American Institute of Physics.

A comparison of unipolar and bipolar electrodes during cardiac mapping studies

Controversy exists as to whether the unipolar or bipolar electrode configuration is superior in detecting local activations during cardiac mapping studies. However, the strengths and weaknesses of each mode suggest that they may provide complementary information. To examine the relative merits of unipolar and bipolar electrode configurations, recordings by each were simultaneously acquired during episodes of ventricular tachycardia in eight consecutive patients undergoing map guided arrhythmia surgery. Unipolar electrograms were classified as either unambiguous or ambiguous according to whether or not they were polyphasic in nature. The activation times from the unambiguous electrograms were compared with activation times from the corresponding bipolar signals where local activation was measured both at the signal's peak amplitude (BI-PK), and at the point at which the waveform's first major, rapid transient crossed baseline (BI-TRN). Occurrences of discrete diastolic activations were also quantified from the unipolar and bipolar tracings. From a total of 415 unipolar electrograms, 301 unambiguous signals were identified as suitable for comparison with the bipolar signals. Both BI-PK and BI-TRN criteria for the determination of local activation were highly correlated with and not significantly different from the local activation from the unipolar electrogram. From 85 ambiguous unipolar electrograms, it was possible to determine local activation from the corresponding bipolar signal in 33% of the occurrences. From the eight patients, 64 diastolic potentials were recorded of which 42 were seen only in bipolar mode, 7 in only unipolar mode, and 15 were evident in both tracings. The prevalence of diastolic potentials was significantly greater in recordings made using bipolar mode. The results demonstrate that complementary information regarding local activations and diastolic potentials can be derived from unipolar and bipolar recordings and suggest that both electrode configurations should be used in multichannel cardiac mapping systems.

Wave mapping: detection of co-existing multiple wavefronts in high-resolution electrical mapping

High-resolution mapping makes it possible to reconstruct and display the conduction pattern of the action potential as it propagates through cardiac or smooth muscles. During slow and regular activity, time mapping of the spread of activation muscles. During slow and regular activity, time mapping of the spread of activation is relatively simple and straightforward. However, when frequencies are high or conduction is slow, such as seen during atrial fibrillation or found in the pregnant uterus, the tracking of individual waves may become more difficult and uncertain. In order to reconstruct the pathway of a single wave, a search and sorting routine was developed which makes it possible to distinguish, track and display individual wavelets. The algorithm is able to detect variations in conduction block, spontaneous shifts in the location of the pacemaker and changes in the direction of conduction. It is less sensitive when two or more wavefronts intermingle in space and time, such as during collision or fusion. Wave mapping is especially useful, in addition to current time mapping, in sorting quickly through the large amount of data produced by high-resolution mapping of electrical activities in cardiac and smooth muscle.

Spectral analysis of activation time sequences

Adequate spatial resolution of local activation is fundamental for the correct depiction of myocardial activation during ablative treatment of ventricular tachycardia. The widest allowable distances between recording sites that provide an accurate description of the field potential distribution is dictated by the Nyquist sampling theorem. Activation times are derived from the field potentials. However, because of noise intrinsic in activation detection algorithms, closer recording sites may be required than those theoretically computed. The purpose of this study is to examine the spatial frequency spectrum of epicardial activation time sequences computed by common activation detection algorithms, determine which algorithm is least noisy, and derive the recording site density necessary to avoid distortion of the epicardial activation map. Using 40 to 80 electrode linear arrays, monopolar and bipolar electrograms from the epicardium were recorded vertically (base to apex) and horizontally in 11 dogs. Activation times for bipolar electrograms were estimated using Peak, Fastest Zero Crossing, and Morphological algorithms. Activation times for monopolar electrograms were set equal to the time of the fastest negative deflection. Activation time sequences were analyzed using conventional Fourier techniques. Anomalous activation times from serially adjacent bipolar electrograms, which constitute algorithm noise, were studied. Horizontal and vertical interelectrode distances are 3.2 mm and 2.4 mm, respectively. Of the bipolar algorithms, the Morphological algorithm produced the fewest anomalous activation times. Mapping systems having more than 256 channels are required for accurate representation of epicardial activation in a typical 20-kg dog. The endocardial electrode spacing is unknown, but is expected to be at least as dense. Large global mapping systems or regionally dense arrays may offer advantages during catheter ablations for ventricular tachycardia and for studies into the mechanisms of ventricular tachycardia by accurately defining the cardiac activation pattern.

Simultaneously collected monopolar and discrete bipolar electrograms: comparison of activation time detection algorithms

Designation of the time of local activation is fundamental to electrophysiological mapping. In normal myocardium, the minimum slope in extracellular monopolar (MP) electrograms has been linked through simultaneous intracellular and extracellular recordings to phase 0 of the action potential. However, no similar correlation has been demonstrated for a parameter from bipolar (BP) electrograms, now commonly used during electrophysiological studies and intraoperative mapping. The purpose of this work is to compare the activation time, determined according to several common algorithms applied to BP electrograms, with the time of the minimum slope in MP electrograms. Simultaneous normal epicardial MP and BP electrograms were acquired from subjects undergoing surgery for Wolf-Parkinson-White Syndrome and from dogs. The activation time in BP electrograms was defined by four algorithms: (1) peak (P); (2) greatest absolute slope (S); (3) zero crossing of the segment containing the greatest slope (FZC); and (4) morphological (M). Each was compared to the time of the minimum slope in the simultaneously recorded MP response. The incidence of outliers was tabulated. The distribution of activation times computed using each BP algorithm was statistically different from the distribution of activation times derived from MP electrograms. M performed best (absolute difference: 2.6 +/- 2.9 msec; cor coef: 0.9925 in man). The M, P, FZC, and S algorithms produced 3.2%, 3.5%, 4.7% and 4.7% outliers, respectively. The overall performance of a morphologically based algorithm is superior to simplistic BP algorithms based only on slope or peak.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of time of sampling onset on parameters used for activation time determination in computerized intraoperative mapping

The purpose of this work is to determine the sensitivity of the estimated time of peaks and maximum slopes, commonly used in activation time computations, to the instant at which sampling is initiated. Based on complex and quickly changing waveforms, 471 monopolar (MP) and bipolar (BP) epicardial responses in man were selected. These were decimated from 10 kHz to simulate sampling at frequencies ranging from 200 Hz to 2,000 Hz. The peak and maximum absolute slope for BP and the minimum slope for MP were computed repeatedly starting at successive 100 microseconds intervals extending throughout the sampling period and compared with these parameters computed from the waveform sampled at 10 kHz. Slopes were estimated using each of four different algorithms. The average greatest shift (AGS) due to variations in sampling onset ranged from 11.2 +/- 3.5 (200 Hz) to 0.3 +/- 0.2 msec (2,000 Hz). For bipolar algorithms, the peak performed better than the slope algorithms (AGS: 5.9 +/- 3.3 to 0.3 +/- 1.0 msec). For MP algorithms, 2 point linear, and 3 and 5 point Lagrange slope estimates performed similarly (AGS: 5.6 +/- 3.3 to 0.3 +/- 0.2 msec); a 5 point least square fit algorithm performed poorly. Sampling MP and BP electrograms below 500 and 400, respectively, often caused maximum shifts greater than 4 msec. Thus, the resolution of the peak and estimated slope is not limited to the sampling period, variations in initiation of sampling can cause significant outliers especially at low sampling rates, and MP electrograms should be sampled faster than BP electrograms for comparable accuracy.

Computer-enhanced mapping of activation sequences in the surgical treatment of supraventricular arrhythmias

Surgical treatment of accessory pathways and ectopic foci requires accurate information on the physical locations of the arrhythmogenic substrates. Although electrophysiology studies during cardiac catheterization frequently provide accurate and reliable data, the physical locations of the sites to be ablated must be verified in situ by electrical activity mapping. We have developed a microcomputer-based system that facilitates creation of electrical activity maps, supplanting the manual method formerly used. Signals produced by mapping and reference electrodes, as well as cardiac diagrams with grid coordinates and times, are presented on a monitor in formats that are easily interpreted by the surgeon and cardiologist. The system is rapid, accurate, and reliable, and has reduced the time required to localize conduction abnormalities from 30 to 45 minutes for the manual method, down to an average of 12 minutes per case. The system is simple to operate, requiring only minimal training. All of the components of the system are commercially available; no specialized hardware is required.

Epicardial mapping: how to measure local activation?

Epicardial ventricular mapping was performed in 5 dogs during sinus rhythm with a sock array containing 41 electrodes. Maps were generated with a computer-assisted mapping system using four different definitions of local epicardial activation: (1) maximal negative slope (intrinsic deflection) of the unipolar electrogram, (2) maximal slope of the bipolar electrogram, (3) maximal amplitude of the bipolar electrogram, and (4) first onset by 45 degrees from the baseline of the bipolar electrogram. The site of earliest and latest epicardial activation was identical with maximal negative slope in the unipolar electrogram and maximal slope and maximal amplitude of the bipolar electrogram in all five animals. Times of earliest and latest epicardial activation calculated with maximal amplitude of the bipolar electrogram were most similar to those evaluated with maximal negative slope of the unipolar electrogram. Using onset of the bipolar electrogram, activation times were measured 10 to 12 msec earlier than with each of the other three definitions of local activation, and in two of the five animals, first epicardial breakthrough was mapped to a different site than with the three other methods.

CONCLUSIONS

(1) Maximal amplitude of the bipolar electrogram coincided with maximal negative slope of the unipolar electrogram; (2) Using onset of the bipolar electrogram, timing and location of earliest epicardial activation may be misinterpreted.

The assumptions of isochronal cardiac mapping

Isochronal maps of cardiac activation are commonly used to study the mechanisms and to guide the ablative therapies of arrhythmias. Little has been written about the assumptions implicit in the construction and use of isochronal cardiac maps. These assumptions include the following: (1) the location of the recording electrodes is known with sufficient accuracy to determine the mechanism of an arrhythmia or to guide therapy; (2) a single, discrete activation time can be assigned to each recording electrode location; (3) the presence or absence of activation at an electrode site can be reliable ascertained, and when activation is present, the time of activation can be determined with sufficient accuracy to specify the mechanism of an arrhythmia or to guide therapy; and (4) the recording electrodes are close enough together that the activation sequence can be estimated with sufficient accuracy to determine the mechanism of an arrhythmia or to guide therapy. The manuscript reviews evidence that these assumptions may not always be true, and when they are not, the isochronal map may be misleading.

Surgical treatment of arrhythmias

Surgical treatment of arrhythmias is often more expeditious and more cost-effective in the long run than pharmacologic therapy. In the past, surgical treatment of arrhythmias has been reserved for patients with disabling paroxysmal or incessant tachycardia refractory to medical management, severe life-threatening arrhythmia or aborted episodes of sudden death. However, tachyarrhythmias that are refractory to pharmacologic therapy because of drug inefficacy, noncompliance or limiting side effects are not uncommon. Although nonpharmacologic treatment of arrhythmias carries with it a one-time period of higher risk (i.e., when the patient undergoes surgery), it is curative and often preferable to the uncertainty and possibly higher cumulative risk associated with medical management.

Simultaneous multichannel cardiac mapping systems

There is much current interest in simultaneous multichannel cardiac mapping. In this paper we give recommendations for the construction of a cardiac mapping system. Because the field of cardiac mapping is relatively young, optimum mapping techniques and all possible applications have not yet been developed. Therefore, the mapping system should be flexible and it should have many capabilities. The system should be digital; if variable gains are used, the amplifiers should be programmable and controlled by a microprocessor. It should be possible to analyze previous recordings and acquire additional recordings simultaneously. The mapping system should be able to record continuously for at least tens of minutes and preferably for hours. The recorded data stream should be a self-contained unit, holding all important electrophysiologic information as well as the recorded electrode signals. The programs should be written in C under a UNIX operating system. A minimum of 64 channels should be used for epicardial or endocardial mapping and a minimum of 128 channels for three-dimensional intramural mapping. The leakage current requirements for multichannel mapping systems are too stringent and should be re-evaluated. The major limitation to progress in cardiac mapping is neither the hardware nor the software; it is the electrode: its construction, its placement, its fixation, and the interpretation of its recordings.

A new sock electrode for recording epicardial activation from the human heart: one size fits all

Simultaneous recording of epicardial activation from multiple sites during open heart surgery is essential for studying unstable ventricular arrhythmias. A previously described sock electrode array for this purpose requires custom-woven nylon sock material and expensive machined button electrodes. The limited compliance and elasticity of nylon requires that a new sock be individually fitted for each heart. Despite careful fitting, 17-20% of electrodes do not make satisfactory epicardial contact in dogs. Further, electrodes frequently dislodge from the sock and wires break at the button electrode solder joint. Recognizing these limitations, we formed a new sock from Xspan tubular dressing material and devised electrodes that attach securely to the sock. In six dogs, 90% +/- 3% of electrodes made satisfactory contact using the same Xspan sock, significantly (p less than .01) more than with the nylon sock despite far less labor. The same size X span sock with 60 snap electrodes was used to record from 27 human hearts of widely different dimensions. Satisfactory epicardial contact was obtained in 90% +/- 14% of electrodes in the 18 patients with Wolff-Parkinson-White syndrome (WPW) and 75% +/- 15% of electrodes in the nine patients with coronary artery disease. In no case did an accessory pathway fail to conduct following sock placement. The hemodynamic effect of the Xspan sock was evaluated in four dogs and was found to be minimal. Both the Xspan sock and the snap electrodes are easily made from inexpensive, readily available materials. The same Xspan sock accommodates a wide range of heart sizes, and the electrodes supported by the Xspan sock record significantly better and with less dislodgement and wire breakage than previous socks.

Computer-assisted intraoperative mapping of the entire ventricular epicardium in the Wolff-Parkinson-White syndrome

Intraoperative mapping with a hand-held, roving electrode requires a sustained rhythm lasting 5 to 10 minutes. To overcome this limitation, a computerized mapping system that records from 60 epicardial electrodes simultaneously was used to study 16 patients with Wolff-Parkinson-White syndrome. A sock containing 6 rows of electrodes arranged concentrically from base to apex was place over the ventricles. The total time from placing the sock to analyzing the most basal row of electrode recordings was 5 minutes. A 39 X 44-mm plaque containing 56 electrodes was than placed across the atrioventricular (AV) groove for detailed simultaneous mapping of the ventricle and atrium in the preexcited region identified from the most basal row of sock electrodes. During plaque placement and recording, the remaining sock recordings were analyzed and a complete isochronal epicardial map was drawn. The plaque recordings were then analyzed. This technique rapidly detects early activation at the AV groove as do other computer systems using only a band of electrodes around the AV groove. Also, complete epicardial mapping supplied important additional information. One patient with a posterior paraseptal accessory pathway had ventricular epicardial breakthrough below the strip recorded by the AV band. When more than 1 early activation site was present along the AV groove, complete maps allowed multiple pathways to be differentiated from normal activation fronts ascending from the bundle branches. Complete epicardial maps allowed the study of rapidly changing or short-lived electrical events including isolated premature impulses, initiation and termination of reciprocating tachycardia by pacing, entrainment and changing degrees of fusion created by pacing during reciprocating tachycardia, and ventricular responses during atrial fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

On-line mapping system for the visualization of the electrical activation of the heart

A simple but still versatile datalogging system based on a VCR (video cassette recorder) has been developed. The VCR allows mass storage of data originating from a maximum of 256 channels as used, for example, in the recording of the time-dependent potential distribution at the surface of the myocardium. Incorporated in the system is a display memory allowing on-line simultaneous visualization of the assessed recordings of 16 channels. On an interactive base display parameters (time-window, channel-selection) can be altered without loss of data. A link with a personal computer allows modification of system parameters and storage of data for off-line analysis of the recorded data. The high data rate to and from the VCR (4.3 MHz) fully utilizes the bandwidth available. A normal videotape can, therefore, contain up to 2 Gigabyte of data. Despite this, the use of the tapecounter and the decoding of the time-code inserted into the signal allows quick retrieval of the stored data without needing expensive equipment. The system described brings mass data logging within the reach of a vast number of laboratoria and cardiovascular centers.

A digital timing and display unit for intraoperative mapping of cardiac arrhythmias

An inexpensive display and timing unit incorporating a multichannel signal delay has been developed for mapping the heart during electrophysiological surgery. It provides a continuous digital readout of the time relationships between 3 intracardiac electrograms and the surface electrocardiogram. The electrograms are displayed on a storage oscilloscope with an automatic erase facility. This unit is used to locate accessory atrioventricular connections in the Wolff-Parkinson-White syndrome, to map ventricular tachycardias and to locate the bundle of His. The design has been refined during 5 years of use in over 200 operative procedures.

On-line epicardial mapping of intraoperative ventricular arrhythmias: initial clinical experience

An on-line automatic mapping system was developed for beat by beat display of epicardial activation during ventricular tachycardia induced at the time of cardiac surgery. A sock array of 110 button electrodes was used to record and display local activation on a video monitor at 8.3 ms intervals. On instant replay in slow motion, epicardial pacing sites were accurately localized to the nearest electrode. Local unipolar electrograms were also recorded, first from the sock array, then from an array of 16 transmural needle electrodes. The epicardial display was verified by retrospective manually derived maps using the recorded epicardial electrograms. In four patients with coronary artery disease and recurrent inducible ventricular tachycardia, earliest epicardial activation was located on slow motion replay within 1 minute. Subendocardial sites of early activation were located within 10 minutes by replay of electrograms from the needle array before ventriculotomy. Transmural and endocardial resection of these sites prevented inducibility of the tachycardia on postoperative electrophysiologic study in three of the four patients. There has been no clinical recurrence of ventricular tachycardia after 3 to 14 months of follow-up despite cessation of antiarrhythmic therapy in three of the patients. This technique has unique advantages over existing mapping methods. It provides beat by beat display of activation sequences so that clinical tachycardias that are short in duration or pleomorphic in configuration now become amenable to mapping. In addition, it markedly shortens total time on cardiopulmonary bypass.

Operative therapy for ventricular arrhythmia

The history of surgical attempts to control ventricular arrhythmia is reviewed and current methodology is presented in detail. The results of the various surgical approaches and future trends in the management of this troublesome condition are discussed.

Clinical instrumentation for the intra-operative mapping of ventricular arrhythmias

Surgical treatment of ventricular arrhythmias has been greatly facilitated by intra-operative mapping. Present clinical mapping techniques are time-consuming, of limited accuracy, and are restricted to monoform sustained tachycardias. A previously reported on-line cardiac mapping system used in the research laboratory has been modified to provide epicardial maps of ventricular arrhythmias induced at the time of surgery. Changes such as a battery-operated multiplexer, patient electrical isolation, adjustable electrogram gain, time-code labeling and marker-matrix display, have all contributed to the intra-operative application of the original analog real-time mapping technique. These modifications were accomplished without compromising the spatial or temporal resolution (0.5 cm and 8.3 ms) of the laboratory system. An advantage of the present system is a decrease in cardiopulmonary bypass time as a direct result of the instantaneous analysis and display of epicardial activation information. In addition, it enables, for the first time, short salvos and polymorphic runs of ventricular tachycardia to be mapped intra-operatively.

Identification of reproducible ventricular tachycardia in a canine model

Epicardial mapping was used as a standard to investigate how well the limb leads, both alone and in conjunction with 5 select epicardial electrodes, can verify reproducibility in a common, open-chest canine model of ventricular tachycardia (VT). Reproducible VT was defined as 2 or more episodes of monomorphic VT with similar rates, limb lead tracings and epicardial maps. In this study, 21 dogs underwent 2-hour occlusion of the left anterior descending coronary artery followed by reperfusion. Three days later, programmed stimulation was used to induce VT that was analyzed with limb leads I, II and III and 27 simultaneously recorded, bipolar epicardial electrodes. Thirteen dogs had VT of which 11 had polymorphic VT (varying QRS morphology). Twelve dogs yielded at least 1 form of monomorphic VT. Eight had 2 or more distinct forms of monomorphic VT (pleomorphism). Four of these 8 dogs had pleomorphic VT that was not apparent from the limb lead tracings, but was recognized from the epicardial activation maps constructed from the 27 epicardial recordings. To provide a method of distinguishing various VTs without the need of full epicardial mapping, 5 of the 27 epicardial electrodes were selected. These were positioned over the midanterior and midposterior right and left ventricles, and the left ventricular apex. By analyzing electrogram morphology and activation time, VT reproducibility could be as accurately identified with these 5 electrodes as with epicardial mapping derived from 27 electrodes. In conclusion, multiple VT morphologies are common in this open-chest canine model. Limb lead recordings alone are inadequate for analysis of VT reproducibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Late fractionated potentials and continuous electrical activity caused by electrode motion

Late fractionated potentials, recorded during cardiac mapping to find the source of a ventricular arrhythmia, have been ascribed particular localizing value. Re-entry is assumed when these highly amplified and filtered recordings span diastole during tachycardia. The purpose of this study was to see if such potentials can occur artifactually. A saline soaked 7 X 2 X 3 cm sponge was sewn to the epicardium of the right ventricle in five non-infarcted, open-chest dogs. Two bipolar button electrodes, one with 1 mm and one with 1 cm interelectrode spacing, were attached to the outer surface of the sponge and a bipolar wire hook electrode was placed just under the outer surface of the sponge. Thus all three electrodes were 3 cm from the nearest myocardium yet still subjected to cardiac motion. The electrodes were recorded at gains of 4,000-40,000 and filtered to pass 50-300 hertz. One to three rapid deflections were recorded during the QRS from all electrodes. In seven of the the 15 electrode recordings, two or three additional deflections, 1100-200 microV in amplitude, occurred after the QRS. These late potentials were fractionated and recurred reproducibly from cycle to cycle. In two cases, these late fractionated potentials could be made to span diastole by rapid pacing to simulate tachycardia. Clamping the sponge to sliminate motion between the sponge and electrode caused this late activity to disappear. Thus, in highly amplified and filtered recordings, electrode motion can cause artifacts resembling late fractionated potentials and continuous electrode activity.

Anatomic-electrophysiologic basis for the surgical treatment of refractory ischemic ventricular tachycardia

Recently developed surgical procedures for the treatment of refractory ischemic ventricular tachycardia have significantly improved the prognosis of patients experiencing these life-threatening arrhythmias. Ventricular tachyarrhythmias associated with ischemic heart disease most commonly originate from the ischemic border zone of myocardial infarctions, where the non-uniformity of tissue injury is most prominent. The inhomogeneity in tissue injury results in desynchronization of electrical wavefront propagation through the ischemic myocardium, thus providing the milieu necessary for the development of micro-reentrant circuits that give rise to the ventricular tachyarrhythmias. Preoperative and intraoperative electrophysiologic mapping techniques are capable of characterizing and localizing such arrhythmogenic myocardium sufficiently to direct the surgeon in his operative approach to the treatment of the arrhythmia. Surgical options include the encircling endocardial ventriculotomy, the endocardial resection procedure, endocardial cryoablation, and combinations or modifications of these three basic procedures. The use of these procedures has made the previously employed indirect surgical procedures obsolete for the treatment of refractory ischemic ventricular tachyarrhythmias.

Localization of septal pacing sites in the dog heart by epicardial mapping

To examine whether different septal pacing sites could be distinguished by their epicardial activation patterns, six to eight stimulating electrodes were placed throughout the septum in seven open chest dogs. Unipolar electrograms were obtained from 52 epicardial electrodes during pacing from each stimulating electrode and isochronous epicardial maps were constructed. The location of each stimulating electrode was found by dissection, and its distance from the overlying epicardium was measured. To allow comparison among epicardial maps, the septum was conceptually subdivided into nine regions to which stimulating electrodes were assigned. Epicardial activation patterns from the same region were similar and these patterns allowed the region containing a stimulating electrode to be identified in many cases. Three other variables were found to have additional localizing value. There were: 1) the time from the stimulus to epicardial breakthrough, 2) the duration of epicardial activation, and 3) the area of epicardium activated in the first 5 ms after epicardial breakthrough. For those stimulating electrodes that could not be localized by their epicardial activation patterns, the distance of the stimulating electrode beneath the epicardium was well fit from these three variables by multiple regression (correlation coefficient [r] = 0.97). Thus, using all the previous factors, localization of septal pacing sites was possible in the noninfarcted dog heart by epicardial mapping.