Ian Parson

Activation sequence of ventricular tachycardia: Endocardial and epicardial mapping studies in the human ventricle

Thirty-five patients with ischemic heart disease and ventricular arrhythmias underwent intraoperative activation mapping at the time of coronary artery bypass surgery. During ventricular tachycardia, the sequence of activation in the intact ventricle was recorded simultaneously from 110 endocardial or 110 epicardial sites, or both. A balloon array of electrodes, inserted across the mitral valve, was used to obtain endocardial recordings in the left ventricle, and this appeared to facilitate the induction of ventricular tachycardia. Of 61 episodes of tachycardia, 16 (15 patients) were recorded with the epicardial sock and 45 (20 patients) with the additional use of the endocardial balloon. The sequence of activation during tachycardia was observed to conform to one of four configurations: monoregional spread was the most common activation sequence recorded on both the endocardium and epicardium, while biregional activation and figure eight sequences were recorded exclusively on the epicardium and endocardium, respectively. The fourth sequence was a circular spread of activation observed on both surfaces. Continuous activation throughout the tachycardia cycle length was an infrequent finding. Simultaneous recordings of endocardial and epicardial activation were obtained in 45% of episodes. The sequence of activation recorded on one surface was matched by a similar sequence on the remaining surface in less than half of these. The onset of endocardial activation preceded that of the epicardium in greater than 90% of tachycardia episodes, and the duration of left ventricular endocardial excitation often exceeded that recorded epicardially over both ventricles. The epicardium, however, did appear to be an important determinant of surface electrocardiographic configuration.

A Three-Dimensional Display for Cardiac Activation Mapping

A three‐dimensional display is described that allows activation sequences from the epicardium and endocardium to be shown simultaneously on the same image. Three electrode arrays (epicardial sock, left ventricular balloon, right ventricular balloon) are represented in a three‐dimensional perspective by an array of dots that are intensified when activated. This arrangement requires fewer calculations and is easier to interpret than siiced‐isochronal maps but cannot represent a complete heart cycle in one image. The three‐dimensional display eliminates the distortion caused by two‐dimensional diagrams and facilitates activation correlation between electrode arrays. A standard, low cost microcomputer has been used to implement the activation display.

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.

Multichannel recording of cardiac potentials

An inexpensive system for the simultaneous recording of 256 cardiac electrograms is described. Time division multiplexing of cardiac potentials by digital circuitry provides a single video signal which is recorded on video tape. During playback a demultiplexer reassembles the separate signals. Measured channel characteristics demonstrate a bandwidth of 170 Hz, a noise level of 0·2 mV peak-to-peak, and a crosstalk of −27·5 dB. The design has flexibility in that individual channel bandwidth can be exchanged with the total number of channels according to the dictates of signal requirements. To illustrate this flexibility a second system is described which provides 64 channels whose measured characteristics include an 880 Hz bandwidth, a noise level of 0·14 mV peak-to-peak and a crosstalk of −33 dB.

Cardiac Mapping Instrumentation for the Instantaneous Display of Endocardial and Epicardial Activation

A real-time mapping system is described that allows instant display of both endocardial and epicardial activation as monitored by an array of transmural plunge-needle electrodes in the intact in situ heart. From the total cardiac muscle mass, 768 electrograms are recorded, with a programmable feature allowing the rapid and unrestricted selection of 110 endocardial electrograms for automated analysis. An activation analyzer (consisting of parallel analog circuitry) provides an activation image in real time, while video recorders provide both raw and processed data storage with the capability of immediate slow-motion replay. The nature of the data acquisition (110 plunge needles) limits this system to the experimental arrhythmia laboratory where its chief advantage is the enabling of the multichannel recording of endo data without the complications of open heart surgery. Equally important is the ability to automatically store the endocardial activation image locked in time to the simultaneously recorded epicardial image.

The construction of endocardial balloon arrays for cardiac mapping.

The advent of multichannel recording systems has enabled chinical mapping to be performed on a beat‐by‐beat basis using multi‐electrode arrays. Surgical ablation of ventricular arrhythmias generally requires endocardial mapping, Clinical usage has indicated that an inflatable balloon array is the most practical design and can obviate the need for ventriculotomy by a transatrial introduction in the deflated state. Successful experience with the left ventricular balloon led to the development of a right ventricular balloon array suitably configured to extend into the outflow tract. Custom moulds are used to create an appropriate balloon from liquid latex. Nylon cloth is cut from a cardboard pattern to fashion a stretchable sock to envelope the balloon. Electrodes are formed by stitching 2‐mm silver beads to the balloon sock in a preconfigured pattern. Teflon‐coated 31 G multi‐strand stainless‐steel wires 130 mm in length connect the electrode beads by solder to the multipin connectors for easy hookup to the amplifier inputs. Tygon tubing 0.53 cm in diameter fitted to the balloon allows inflation and pressure monitoring. This basic design has been successfully implemented for the last 6 years.

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.

Simultaneous Unipolar and Bipolar Recording of Cardiac Electrical Activity

An analog mapping system using a true bipolar left ventricular balloon electrode array is described, which enables simultaneous unipolar and bipolar recordings. It is an adaptation of a previous clinical analog mapping system used in the investigation of ventricular arrhythmias. The bipolar balloon array consists of 112 electrode pairs, each having a 2‐mm separation. The signals from the electrodes are sensed in parallel by separate unipolar and bipolar amplifier units, which then drive a common multiplexer bus. The bipolar recording unit consists of high quality instrumentation amplifiers with adjustable gain and exhibits a full bandwidth minimum common mode rejection of 78 dB. Using this combination, it is possible to record local cardiac micropotentials while still retaining the advantages of unipolar electrograms to track overall cardiac activation.

Phospholipase-Induced Abnormalities in the Sarcolemma

Phospholipids are the major form of lipid in all cell membranes and their fixed composition and disposition within membranes are genetically predetermined. In combination with other lipids and proteins, phospholipids are responsible for both structural characteristics and functional properties of the biological membranes such as fluidity (1, 2), ionic permeability (3, 4), transport of material across cell membranes (5), activities of a large number of membrane-bound enzymes (6) and receptor-mediated cell responses (7, 8). Phospholipases are the enzymatic systems responsible for the catabolism of membrane phospholipids, and the interplay between these catabolic enzymes and those of anabolic systems determines the turnover rate and maintains the biological properties and fixed composition of these lipids in membranes. Various physiological stimuli (e.g. certain hormone-receptor interactions, increase in intracellular Ca2+, fat absorption, etc.) enhance phospholipid turnover in membranes (8–11). In some disease conditions, membrane phospholipid composition and metabolism are progressively altered resulting in the functional abnormalities of the cell (12–15).