Intraoperative Cardiac Mapping Research Articles

Endocardial mapping of ventricular tachycardia in the intact human ventricle. III. Evidence of multiuse reentry with spontaneous and induced block in portions of reentrant path complex

Objectives. This study was conducted to characterized the functional nature of the reentrant tract responsible for ventricular tachycardia due to ischemic heart disease.Background. A zone of slow conduction forming the return path is thought to form a critical component of the reentrant mechanism in ventricular tachycardia. Despite its importance, detailed knowledge of the return path is rare in clinical studies.Methods. Multielectrode arrays were used intraoperatively to obtain unipolar and high gain bipolar recordings of left ventricular endocardium in patients undergoing map-directed surgical ablation of ventricular tachycardia. A total of 224 local elerograms were analyzed for each tachycardia.Results. Of 10 consecutive patients undergoing intraoperative cardiac mapping, detailed recordings of the return tracts of eight ventricular tachycardias were obtained in three patients. The recordings demonstrated that returnstracts can be complex and extensive, with multiple paths of entry and exit. Potential and actual alternate paths were observed. Spontaneous and induced block occurred within portions of the complex. Intermittent block in one of two paths of entry resulted in intermittent cycle length changes of the tachycardia without a change in configuration. Block in one exit path resulted in a shift to alternative exit paths, with dramatic changes in ventricular activation and tachycardia configuration. Termination of the tachycardia could result from block close to the entrant or exit portion of the return tract. Different tachycardias were seen to share common portionsof a return tract.Conclusions. These observationis enlarge and extend our knowledge of the functional repertoire of complex reentrant tracts that occur in infarct-related ventricular tachycardia. The use of common portions of a reentrant tract by several tachycardias is confirmed. Utilization of alternate pathways can account for changes in configurationi and cycle length. Spontaneous and induced block can occur at points of entry and exit in a reentrant tract and may identify optimal targets for ablation attempts. Further advances will require greater emphasison diastolic activation mapping.

Intraoperative mapping is not necessary for VT surgery.

Surgical ablation of ventricular tachycardia is generally guided by the results of pre- and intraoperative cardiac mapping. However, in certain situations intraoperative cardiac mapping may not be possible and, therefore, surgery has to be based on information obtained preoperatively. This raises the question whether intraoperative mapping is necessary for the success of this approach. We describe our experience with encircling endocardial cryoablation for ischemic VT and examine the contribution of intraoperative mapping for this procedure. Thirty-three patients with inducible VT refractory to medical therapy and a well defined anatomic scar were considered for surgery. All patients underwent baseline electrophysiology study and intraoperative mapping was attempted during normothermic cardiopulmonary bypass. In 14 patients, VT was inducible intraoperatively (Group 1) and surgical ablation was guided by this information, whereas in 19 patients, VT could not be mapped for various reasons (Group 2). Reasons for failure to obtain intraoperative map included noninducibility (3), nonsustained VT (8), polymorphic VT (4), VF (3), and incessant VT with hemodynamic collapse and cardiac arrest (1). The two groups did not differ with respect to age, location of myocardial infarction, or preoperative left ventricular ejection fraction. The operative procedures were similar in the two groups with respect to aortic cross clamp time, cardiopulmonary bypass time, number of cryoablation lesions, concomitant revascularization, aneurysmectomy, and ICD implantation. Encircling endocardial cryoablation was performed in 32 patients and one patient underwent partial right ventricular free wall disconnection (RV infarct). Thirteen patients underwent concomitant coronary artery bypass grafting (5 in Group 1 and 8 in group 2). One patient had prophylactic ICD patches (Group 1).(ABSTRACT TRUNCATED AT 250 WORDS)

Supraventricular Tachycardias: The Role of Surgery

Because of its high efficacy and low morbidity radiofrequency energy catheter ablation techniques have toppled the hierarchy of choice in the electrophysiological intervention armamentum. This review assesses current role of surgery and its foreseeable future. Most accessory AV pathways can be attained by endocardial manipulation and ablated. Surgical dissection of accessory pathways on the beating heart had documented that most pathways were paraannular, although right-sided pathways may be distant to the annulus. Results of accessory pathway ablation have shown that right-sided pathways are difficult to approach and ablate. Surgical ablation may currently be considered after failed catheter ablation. AV nodal modification using catheter ablation also yields excellent results. Radiofrequency energy creates a discrete lesion associated with discrete electrophysiological alteration. Surgical dissection is associated with more diffuse and extensive anatomical and electrophysiological changes and is no longer used even after failed catheter ablation. The arrhythmogenic anatomical substrate associated with atrial flutter is not yet well delineated in the coronary sinus os region. How to extend tissue modification for uniform success here is not yet known. Further surgical approach combined with extensive intraoperative cardiac mapping may ultimately prove a valuable guide for subsequent catheter technique. Atrial fibrillation is the last surgical frontier unchallenged by catheter techniques. Arrhythmogenic anatomical substrate is diffuse spreading over the entire atrial myocardium without a discrete target. The associated pathology is diffuse, severe, and progressive and present even in the so-called lone atrial fibrillation. Progression of underlying pathology can nullify the best designed surgical rationale in terms of sinus node chronotropic function, and atrial contractility. Currently used surgical techniques, i.e., the corridor and the Maze operations, have contributed to a better selection of patients. Surgery is still associated with significant morbidity and relative efficacy, and may be improved before becoming the electrophysiological intervention of choice for atrial fibrillation. In conclusion, atrial fibrillation is a greater surgical challenge, but has to be met with the same standard used for other supraventricular tachycardias.

Activation Time Detection Algorithms Used in Computerized Intraoperative Cardiac Mapping: A Comparison with Manually Determined Activation Times

Activation Time Detection for Intraoperative Mapping. Introduction: Local activation determined from monopolar electrograms usually is marked at the time of the minimum slope. In bipolar recordings, the peak, the maximum absolute slope, the baseline crossing of the segment containing the maximum absolute slope, and morphological criteria have been used. The purpose of this work is: (1) to compare activation times determined using these algorithms with activation times corrected by electrophysiologists; and (2) to determine which computerized algorithm requires fewest operator correction of outliers. Methods and Results: Monopolar and bipolar electrograms were collected from the epicardium of subjects undergoing surgery for ventricular tachycardia and Wolff‐Parkinson‐White syndrome, and the above bipolar and monopolar algorithms were evaluated. The electrophysiologists viewed adjacent channels and evolving isochronal maps but not the computer markings. The morphological algorithm compared most favorably with times marked up by electrophysiologists having an overall average difference of 2.2 ± 3.1 msec. For monopolar data, a five point, least square fit, second‐order slope approximation algorithm most closely agreed with the electrophysiologist corrected algorithm (3.2 ± 4.0 msec). The morphological and least square algorithms also produced the fewest outliers (3.1% and 5.7%, respectively). When outliers were removed, bipolar and monopolar discrepancies were reduced to 1.8 ± 1.9 and 2.5 ± 2.3 msec, respectively. Conclusions: Thus, among those algorithms tested, an algorithm based on morphological criteria is best suited for computer determination of bipolar activation times and compares favorably to variations between electrophysiologist corrected and computer marked activation times determined traditionally by the largest negative slope in monopolar data. Identification of outliers using contextual and improved morphological algorithms may improve computerized mapping system performance.

Design and implementation of a new computerized system for intraoperative cardiac mapping

A rapid, portable, yet inexpensive and expandable computer-based system utilizing current technology has been developed from experience in the operating room. An efficient operating system well suited for surgery is defined. New technology recording arrays fabricated from multielectrode flexible Kapton strips were developed and found to be easy to use and highly reliable. Novel arrays are created easily for research or special clinical applications. The system displays all incoming data in real time and transfers 16-s epochs to disk on command. After the user defines a beat for analysis, the computer determines the activation time for each channel, rejects unsatisfactory channels, and displays the results for review and modification before plotting the isochronal map on the monitor. The average time to recall data and produce a map is 16 s; if manual review of 120 channels is included, mapping time is less than 4 min. Clinical data recorded during surgery are discussed. The speed and operational ease demonstrated in the operating room make this computer/electrode system valuable both for surgery and for elucidating basic mechanisms of arrhythmias.

Bandwidth‐Induced Errors in Parameters Used for Automated Activation Time Determination During Computerized Intraoperative Cardiac Mapping: Theoretical Limits

Two parameters commonly used when determining the time of local activation during computerized intraoperative cardiac mapping are the time of the peak in bipolar electrograms (BP) and the time of the largest negative slope (LNS) in monopolar electrograms (MP). The dependence of these parameters upon bandwidth was studied. A database of fast MP and BP was compiled from intraoperative recordings collected from epicardial sock arrays in man. Based on 95%, 99% and 99.9% of total signal power, the bandwidths of each response were determined. After removing specified frequencies using the Fourier transform, errors in determining these parameters were computed and characterized with respect to mean square error (MSE), percent power bandwidth and frequency content. The Fourier transform was used to abruptly filter out undesired upper frequencies. Filtering BP at 200 Hz produced a 1-ms shift in the peak in 17.0% of the electrograms, 0.4% of the peaks shifted by 2 ms and none shifted by more than 2 ms. Comparable shifts in the LNS occurred when filtering MP at 400 Hz. Retention of 95% of the power in a BP rarely (0.9%) changed the time of its peak by more than 1 ms. For MP, retention of 99.9% of the power was required for similar performance (3.6%). Thus, although BP have greater signal power in the higher frequencies than MP, a greater bandwidth is required when recording monopolarly in order to preserve the small amount of power necessary to define the time of the LNS with accuracy comparable to determination of the peak in BP.

Mechanisms of ventricular tachycardia termination and acceleration during transvenous cardioversion as determined by cardiac mapping in man

We examined the EP mechanisms underlying efficacy and inefficacy of transvenous cardioversion shocks in 13 patients with coronary artery disease and sustained VT during preoperative and intraoperative cardiac mapping procedures. Shocks were delivered at the right ventricular apex with a Medtronic 6880 catheter and a Model 5350 external cardioverter/defibrillator with two or three electrode configurations, resulting in unidirectional or bidirectional shocks, respectively. Single transvenous shocks with incremental energies ranging from 0.03 to 25 J were delivered in sinus rhythm and VT, and simultaneous right and left ventricular electrograms were obtained.Transvenous cardioversion shocks of 0.03 J in sinus rhythm and VT produced immediate local right ventricular depolarization and subsequently conducted to distant right ventricular and left ventricular sites after 30 to 100 msec. Shocks of 0.05 to 0.5 J produced immediate depolarization of progressively larger right ventricular and left ventricular regions, with shocks ≥0.5 J producing immediate depolarization of distant left ventricular sites in sinus rhythm. High energy (>5 J) shocks produced instantaneous depolarization of multiple right ventricular and left ventricular sites in VT. VT termination occurred due to either delay or interruption of conduction in the tachycardia circuit, despite prior depolarization of the early sites of ventricular activation during the QRS complex. This could be due to instantaneous or paced depolarization of critical “excitable” components of the VT circuit, resulting either in immediate conduction block or in instability followed by termination. VT acceleration with transvenous cardioversion was due to modification of the “excitable,” slowly conducting components of the VT circuit with the development of new areas of conduction block, along with altered intra-ventricular conduction. Similar EP mechanisms were observed with unidirectional and bidirectional transvenous shock patterns. We conclude that transvenous shocks alter conduction in human ventricle, and clinical effects of QRS synchronized shocks are related to conduction changes induced in the excitable components of the VT circuit.