The Feasibility of Beat-to-Beat Detection of His-Purkinje Activity by Finite Element Method

A noninvasive method has been applied on human and canine subjects to observe beat-to-beat activity of the His-Purkinje system without using signal averaging. Recordings were performed with multiple Ag/AgCl electrodes, very low noise, high gain amplifiers and by analog filtering. The subjects were in a supine position during the recording. In order to reduce random noise inherent in the high-gain body surface recording, a finite element method (FEM) was applied to calculate His-Purkinje activity. The dimensional relationship between electrode sites, necessary for the calculation, was pre-estimated by x-ray computed tomographs of the subject. A prominent waveform was observed between the atrial and ventricular complexes and corresponded to His bundle activity which was simultaneously recorded by an intracardiac electrode (on every beat). It was, however, difficult to recognize the His-Purkinje activity during inhalation due to the thoracic electromyogram on some human subjects. This interference could theoretically be reduced by increasing the number of body surface electrodes used for this technique.     

Application of Beat-to-Beat Techniques

FLOWERS, N.C., ET AL.: Application of Beat-to-Beat Techniques. The focus of this report is to describe a system for recording surface His-Purkinje and ventricular late potentials on a beat-by-beat basis outside of a shielded environment. An AC magnetic field monitoring device was designed for improved site selection, orientation, and quality control of the acquisition. His-Purkinje signals are detected utilizing spatial averaging and specific channel selection algorithms applied to discriminate random noise from signal. Beat-by-beat vectormagnitude complexes were generated from pairs of X, Y, and Z leads. Both infinite impulse response (IIR) filters, modified for beat-by-beat approaches, and finite impulse response (FIR) filters were utilized. Using the IIR filter, beat-by-beat recordings from test subjects were compared to the signal averaged electrocardiogram (SAECG). Measurement parameters from normal test subjects fell within the previously specified normal range for the SAECG. The IIR filter applied to beat-by-beat recordings exhibited sharp frequency response and a precisely defined cutoff frequency allowing maximal attenuation of the low frequency components in the ST segment. While filter ringing was eliminated, discontinuity and distortion of the filtered waveform resulted. The FIR filter with linear phase response retained the integrity and morphology of the complex but because of its flat frequency response, the ST segment was not as well attenuated and it was more difficult to isolate late potentials. A high order FIR filter should be used if the desire is to match the frequency response of the four-pole IIR filter, since the frequency response of the FIR filter is primarily determined by the order of the filter. With the FIR filter the waveform will be widened on both sides in time and therefore a trade-off results between the order of the filter and the cutoff frequency. A low order and a high cutoff frequency were necessary to attenuate the low frequency components of the ST segment without significantly widening the QRS. To record high resolution ECGs without noticeable 60-Hz noise, the magnetic field of 60 Hz should be smaller than 6.6 × 10^-8 Tesla. This study indicates that real-time analysis of both His-Purkinje potentials and late potentials in an unshielded environment is possible. (PACE, Vol. 13, December, Part II 1990)     

Spatial Differences of the Duration of Ventricular Late Fields in the Signal-Averaged Magnetocardiogram in Patients with Ventricular Late Potentials

Magnetocardiography (MCG) allows one to noninvasively localize cardiac electrical activity in three dimensions. It was the purpose of this study to obtain information about the spatial variations of signal-averoged ventricular Jate magnetic fields recorded by a biomagnetic multichannel system. Biomagnetic signals of 170–600 heart cycles obtained hy the 37-channel system KRENIKON^R (Siemens Medical Engineering Group) were simultaneously averaged in all channels. The absolute values of the filtered signals (digital, bidirectional, four-pole butterworth, bandpass filter [3-dB range, 40–250 Hz]) were calculated in each channel. The noise level was determined within the TP segment. The onset of the terminal low amplitude signals (TLAS) was defined when the signals became lower than 1/23 of R_maxof the QRS complex for the channel with the largest filtered QRS complex after filtering. The TLAS ended when the signal was lower than twice the standard deviation (2 sigma) above the mean noise level. Ventricular late fields were defined as present when the TLAS had a duration of more than 39 msec. In this study, five patients with ventricular late potentials (four with sustained ventricular tachycardia) and three healthy individuals were examined. Ventricular late fields were detected in the patient group in 2–15 MCG channels with a mean length of 49.6 msec (43–60 msec). The spatial distribution of the ventricular late fields was consistently found to exhibit maximum duration in a certain area. In the normal subjects no ventricular late fields were detected. Thus, MCG is able to detect ventricular late fields and their spatial variations. In addition to the information obtained hy signal averaging from the surface ECG, averaging of biomagnetic signals with a multichannel device can reveal spatial inhomogeneity of delayed myocardial excitation.     

Late Potentials and Arrhythmogenesis *

There are three current prognostic indicators of ventricular electrical instability. (1) categorization and siratification of sponlaneous ventricular arrhythmias from standard ECG recordings; (2) programmed electrical stimulation; (3) direct recording of delayed depolarization potentials, usually re/erred to as late potentials. Of the three, the latter offers a new and promising approach. Late potentials represent delayed activation potentials of diseased myocardial zones and may prove to be a strong independent marker of the propensity to develop reentrant ventricular arrhythmias and sudden cardiac electrical death. The problem in identifying late potentials on the body surface is that the signal is smaller than the electrical noise produced by various sources. Two different techniques have been utilized to improve the signal-to-noise ratio: first, signal averaging, which is applicable to regular repelifive electrocardiographic signals but cannot detect moment-to-moment dynamic changes in the signal; second, low-noise or high-resolution electrocardiography that utilizes spatial averaging techniques as well as other noise-reducing measures to record the late potentials on a beat-to-beat basis. This technique has the potential of directly identifying malignant “reentrant” versus benign “focal” ventricular rhythms. The present report discusses the electrophysiologic basis of late potentials and the clinical results of both signal-averaged and low-noise recordings for evaluation of ventricular electrical instability, particularly in patients with ischemic heart disease.     

Septal His-Purkinje Ventricular Pacing in Canines: A New Endocardial Electrode Approach

Ventricular activation sequences and cardiac performance are influenced by pacing sites. Stimulation of or close to the specialized a trioventricular (AV) conduction system optimizes paced ventricular function compared to alternative epi- or endocardial muscle conduction sites. This study reports a new endocardial electrode implant approach to approximate septal His-Purkinje ventricular pacing. Five 6-month-old beagles were used, A custom, platinum-iridium, exposed helical screw electrode (Medtronic, Inc.), 4.5-mm long, with a 17.8-mm² surface area, was designed with a polyurethane covered 4 filar MP35N nickle conductor lead. An 8 French sheath (USCI, Inc.) was modified as introducer to permit simultaneous implant intracardiac pressure and electrogram recordings. Following a thoracotomy, the introducer was inserted through the right atrial appendage and advanced to record optimal His-bundle electrogram while maintaining atrial pressure along the septal tricuspid valve annulus. After electrode implant, ECG demonstrated narrow paced QRS morphology. Mean implant values showed sensed R wave 6,3 mV, slew rate 0.65 V/sec, pacing impedance 319 ohms, and threshold 0.9 V/3.3 mA at 0.5-msec output. Necropsy showed implant above the tricuspid annulus with electrode extension into and contained within the proximal ventricular septum. This study demonstrates that an endocardial septal approach to His-Purkinje ventricular pacing to optimize paced ventricular function is feasible with a new electrode design and precise septal implant technique. Alternative introducer designs may permit tranvenous application of this approach.     

Extension of non-invasive EEG into the kHz range for evoked thalamocortical activity by means of very low noise amplifiers

Ultrafast electroencephalographic signals, having frequencies above 500 Hz, can be observed in somatosensory evoked potential measurements. Usually, these recordings have a poor signal-to-noise ratio (SNR) because weak signals are overlaid by intrinsic noise of much higher amplitude like that generated by biological sources and the amplifier. As an example, recordings at the scalp taken during electrical stimulation of the median nerve show a 600 Hz burst with submicro-volt amplitudes which can be extracted from noise by the use of massive averaging and digital signal processing only. We have investigated this signal by means of a very low noise amplifier made in-house (minimal voltage noise 2.7 nV Hz(-1/2), FET inputs). We examined how the SNR of the data is altered by the bandwidth and the use of amplifiers with different intrinsic amplifier noise levels of 12 and 4.8 nV Hz(-1/2), respectively. By analyzing different frequency contributions of the signal, we found an extremely weak 1 kHz component superimposed onto the well-known 600 Hz burst. Previously such high-frequency electroencephalogram responses around 1 kHz have only been observed by deep brain electrodes implanted for tremor therapy of Parkinson patients. For the non-invasive measurement of such signals, we recommend that amplifier noise should not exceed 4 nV Hz(-1/2).     

Frequency and Significance of Left and Right Ventricular Late Potentials after Myocardial Infarction in Man

Left and right heart catheterization was conducted on 45 patients with a history of myocardial infarction in order to detect so-called ventricular late potentials by means of endocardiac mapping. The endocardiac signals were amplified 100 to 10,000 times at a low noise level using bipolar electrode catheters. The signals were stored unfiltered and visualized directly on an oscilloscope. Consistently recurring late potentials were recorded after QHS complexes in 32 patients (71%). They ranged in amplitude from 50 to 780 μV, while the coupling intervals were measured in the range of 80 to 620 ms from the beginning of the QRS complex to the beginning of the late potential. In some patients, the intracardially registered and/or Holter-monitored ventricular ectopic beats occurred with a delay, corresponding to the delayed occurrence of the ventricular late potentials.     

Reinitiation of ventricular macroreentry within the His-Purkinje system by back-up ventricular pacing - a mechanism of ventricular tachycardia storm

BACKGROUND: We describe immediate reinitiation of macroreentry ventricular tachycardia (VT) involving the His-Purkinje system by ventricular pacing from the electrode of an implantable cardioverter defibrillator (ICD) as a mechanism of VT storm refractory to ICD therapy. METHODS AND RESULTS: Repetitive reinitiation of bundle branch reentry tachycardia (BBRT), interfascicular tachycardia, or both VTs by ventricular pacing was identified in four ICD patients presenting with VT storm or incessant VT. All patients had a pre-existing prolonged HV interval (75 +/- 9 ms) and left bundle branch block (LBBB) or bifascicular block during sinus rhythm. The VTs included BBRT with LBBB in three patients and interfascicular tachycardia with right bundle branch block (RBBB) and left anterior or left posterior fascicular block in two patients. The paced beats from the ICD electrode exhibited a LBBB pattern of depolarization in two patients and a RBBB contour in V1 and V2 with left axis deviation in two patients. The QRS complex during pacing from the ICD electrode closely resembled that of the recurrent VT in all four patients suggesting that the pacing site of the ICD electrode was in proximity to the myocardial exit site of the bundle fascicle used for antegrade conduction during the reinitiated VT. Ventricular pacing from the ICD electrode after termination of the VT apparently encountered the retrograde refractoriness of this bundle fascicle and allowed immediate re-propagation of the wavefront orthodromically along the VT circuit. BBRT was eliminated by ablation of the right bundle branch. Successful ablation of the interfascicular tachycardias was achieved by targeting (1) an abnormal potential of the distal left posterior Purkinje network or (2) a diastolic potential during VT in the midinferior left ventricular (LV) septum. CONCLUSIONS: Repetitive reinitiation of BBRT and interfascicular tachycardia by ventricular pacing from the ICD electrode should be considered as a mechanism of VT storm refractory to ICD therapy in patients with a pre-existing conduction delay within the His-Purkinje system.     

Rapid Ventricular Tachycardia Due to His-Purkinje Reentry

Two patients developed rapid His-Purkinje reentrant tachycardia during programmed ventricular stimulation for evaluation of recurrent ventricular tachycardia. In Patient 1, His-Purkinje reentry induced a morphologically distinct ventricular tachycardia which may have been a reentrant circuit operating independently for several cardiac cycles. His-Purkinje reentry was not inducible in Patient 2 until lidocaine was given. Following lidocaine administration, sustained His-Purkinje reentrant tachycardia was initiated by 2 premature ventricular stimuli. The tachycardia was rapid (240 beats per minute) and required cardioversion.     

Evolution of Late Potentials During the First 8 Hours of Myocardial Infarction Treated with Thrombolysis

It has been demonstrated that successful thrombolytic therapy is associated with a reduction of late potentials in the signal-averaged electrocardiogram (SAECG) recorded within 48 hours after hospital admission. This study extends these observations, using for the first time a longitudinal design investigating whether ischemia and its potential reversal by thrombolytic therapy are associated with dynamic changes in SAECG recordings obtained continuously for 8 hours after the start of therapy in patients with acute myocardial infarction (MI). SAECGs were obtained from 12 patients (2 women and 10 men; ages 63 ± 13 years) with acute MI. The SAECG (X²+ Y²+ Z²)^1/2 was generated with a high pass filter of 40 Hz, noise ≤ 0.3 μV. Comparing the SAECG recordings during the first and eighth hours, there was a significant decrease in filtered QRS duration (fQRS; 119.5 ± 17.1 vs 106.3 ± 15.3 ms) and duration of the low amplitude signals ≤ 40 μV of the terminal QRS (LAS40; 48.8 ± 18 vs 34.2 ± 14.2 ms), and increase of root mean square voltage of the last 40 ms of the QRS (t-RMS; 14.8 ± 9.3 vs 37.8 ± 34.4 μV) (rank test, P ≤ 0.05). In this patient series, there was a significant improvement of fQRS, t-RMS, and LAS40 during the first 8 hours of acute MI, perhaps indicating reversal of ischemia with thrombolysis. Even during acute MI, these markers of delayed conduction allow investigation of intervention induced changes in myocardial conduction and possibly prediction of the patency of the infarct related artery using signal-averaging techniques.     

Effects of alternating cycle lengths on refractoriness of the His-Purkinje system.

The effects of alternating cycle lengths (bigeminal rhythm) on His-Purkinje system refractoriness were studied in 14 patients using His bundle and right bundle recordings. Programmed atrial stimulation at constant cycle length (method I) was scanned using the atrial extrastimulus technique (A2) and compared with an atrial cycle length of identical duration coupled to A2 on alternate beats (method II). The results showed that (a) despite shorter cycle length of the His-Purkinje system with method II due to effect of A2 on atrioventricular nodal conduction (699 +/- 90 vs. 743 +/- 87 ms, P less than 0.001), the relative refractory period of the His-Purkinje system was always longer with method II (463 +/- 52 vs. 440 +/- 43 ms, P less than 0.001). A similar increase also occurred in effective refractory period of the His-Purkinje system; (b) while functional right bundle branch block occurred in eight patients and functional left bundle branch block in two patients with method I, functional right bundle branch block occurred in all 14 patients and left bundle branch block in seven patients with method II; (c) in two patients where both functional right and left bundle branch block occurred with method I this never was manifest at identical degree of abbreviation of His-Purkinje system cycle length but was manifest at identical abbreviation in each of seven patients with method II; (d) site of conduction delay and/or block during functional right bundle branch block was always proximal, i.e., between the His bundle and right bundle recordings with both methods. During method II this resulted in shortening of the subsequent right bundle cycle length relative to the subsequent His bundle (and of necessity left bundle) cycle length. The finding of increased His-Purkinje system refractoriness despite shorter preceding cycle length of the His-Purkinje system during atrial bigeminy has never been previously described and suggests that classical concepts of His-Purkinje system behavior may require revision in this setting. Secondly, during atrial bigeminy the occurrence of alternating functional bundle branch block cannot be accounted for solely by the degree of abbreviation of His-Purkinje system cycle length, but may be explained by a relative shortening of the next ipsilateral bundle branch cycle length in the bundle manifesting block.     

Behavior of postextrasystolic His-Purkinje system refractoriness after multiple premature beats

Although the steady-state refractoriness of the human His-Purkinje system has been shown to be directly related to the cycle length of pacing, the effect that a varying number of premature beats would have on His-Purkinje system refractoriness of the first postextrasystolic beat has not been described. These effects were systematically investigated in 10 patients with normal intraventricular conduction. The His-Purkinje system relative refractory period (HPS-RRP) of the postextrasystolic beat and that of a comparable constant cycle length ventricular drive were measured by the ventricular extrastimulus technique. Results were as follows: the HPS-RRP of the postextrasystolic beat after one premature beat was longer than the HPS-RRP during a comparable constant ventricular drive. However, with the addition of each successive premature beat, the HPS-RRP of the postextrasystolic beat alternated between lower and higher values, in a manner dependent on whether there was an odd or even number of premature beats. In contrast, ventricular refractoriness of the postextrasystolic beats behaved in a cumulative manner, decreasing progressively with the addition of each premature beat.     

Distinct Activation Patterns of Idioventricular Rhythms and Sympathetically-Induced Ventricular Tachycardias in Dogs with Atrioventricular Block

To investigate mechanisms of ventricular impulse formation in response to sympathetic stimulation in the healthy canine heart in situ, we compared the patterns of ventricular activation during the idioventricular rhythms arising after complete atrioventricular (AV) block and ventricular tachycardias induced by RSG or LSG stimulation. Isochronal maps were generated by computer from 116-127 unipolar electrograms recorded from the entire ventricular epicardium in 15 open chest, anesthetized dogs. In eight of these, bipolar electrograms were recorded with plunge electrodes from 11 selected endocardial sites located below epicardial breakthrough areas. Intracardiac recordings from the His-Purkinje system were made with electrode catheters. After electrograms were recorded during sinus rhythm, complete AV block was induced by injecting formaldehyde into the AV node and idioventricular rhythms occurred spontaneously at a rate of 37 +/- 12 beats/min (mean +/- SD, n = 25). During idioventricular rhythms, endocardial activation preceded the earliest epicardial breakthrough, which occurred in either the right anterior paraseptal region, antero-apical left ventricle, or postero-apical left ventricle. These sites were consistent with a focal origin in the subendocardial His-Purkinje system. Total epicardial activation times lasted for 47 +/- 13 msec (n = 40). Idioventricular rhythms were suppressed by overdrive pacing (intermittent trains of ten beats with decremental cycle length from 500 to 200 msec) or by intravenous calcium infusion (to plasma levels of 10.1-15.2 mM). Right or left stellate ganglion stimulation increased idioventricular rhythm rates (to 52 +/- 13 beats/min, n = 28) and also induced, in all preparations, ventricular tachycardias that had significantly faster rates (189 +/- 55 beats/min, n = 27, P less than 0.005). Ventricular fibrillation was induced after brief runs of ventricular tachycardia in five of the preparations. During ventricular tachycardias, epicardial activation occurred on the right ventricular outflow tract or the postero-lateral wall of the left ventricle, and preceded endocardial activation in 50% of cases. Total epicardial activation times (103 +/- 29 beats/min) were significantly longer than during idioventricular rhythms (P less than 0.005). Ventricular tachycardias displayed overdrive excitation at critical pacing cycle lengths (360-280 msec) and were not suppressed by calcium infusion. Thus, differential mechanisms of impulse formation with distinct localizations can be elicited from healthy ventricular myocardium.     

Recording of abnormal late ventricular activity by high-resolution magnetocardiography

High-resolution magnetocardiography (HR-MCG) is a new noninvasive technique for detection of very low-amplitude magnetic fields generated by the electric activity of the heart. We studied 11 patients with documented sustained ventricular tachycardia after myocardial infarction (VT group), 11 patients with old myocardial infarction without ventricular tachycardia (MI group) and 11 normal controls (N group) with HR-MCG and high-resolution electrocardiography (HR-ECG). After averaging and high-pass filtering (25 Hz, 40 Hz, 60 Hz and 80 Hz) the XYZ leads of HR-ECG were combined to vector magnitude and the magnetic recordings from 3 × 3 grid locations were enveloped with Hilbert transformation. Then the QRS duration and the root-mean-square (RMS) amplitude of the last 40 ms, 50 ms and 60 ms of the QRS were calculated. The QRS duration was significantly longer in the VT group compared to the MI and the N group both in HR-MCG and HR-ECG. Also the RMS values were clearly smaller in the VT group with both methods. There were no significant differencies in the diagnostic power of these two methods. The 25 Hz high-pass filtering separated best the VT group from the MI group and the N group. In conclusion HR-MCG is a new non-invasive method for identification of patients at risk of malignant ventricular arrhythmias after myocardial infarction.     

QT dispersion in 120 electrocardiographic leads in patients with structural heart disease

The clinical significance of QT dispersion (QTd) measured in 12-lead ECGs is controversial. The aim of this study was to clarify factors that determine the QTd and its measurement errors in different lead arrays in patients with structural heart disease. Two blinded observers measured QT intervals on a computer screen from 120-channel ECG recordings in a retrospective set of 257 patients, comprising a group of 121 myocardial infarction (MI) survivors without ventricular tachyarrhythmia during a 6-month follow-up and a group of 136 survivors of ventricular tachyarrhythmia/fibrillation. QTd did not differ in patients with and without ventricular tachyarrhythmia/fibrillation. Eleven ventricular tachyarrhythmia/fibrillation survivors without structural heart disease had the lowest QTd (P < or = 0.02). The strongest factor determining QTd and the magnitude of its measurement error was the lead array (P = 0.0001). Measurement errors had two components. The smallest relative errors were in the total body surface mapping array with one component related to interobserver reproducibility (9.1 +/- 7.6%), and the other component related to accuracy of measurement of the QT interval (36 +/- 16%). The authors estimated that a difference of QTd of at least 50 ms between study groups is required in a 12-lead ECG to draw any conclusions from the studies. In patients with structural heart disease, QTd from limited arrays of ECG leads was not a reliable measure. It correlated with the presence of structural heart disease, but not with arrhythmogenicity. An array consisting of ECG leads covering the entire chest allowed better reproducibility and measurement accuracy of QTd.     

Clinical evaluation of an improved high resolution ECG cart for recording the His bundle electrogram non-invasively

The Marquette high resolution MCA-1 ECG cart can record the His bundle electrogram non-invasively at the bedside. The second generation MAC-1 has several unique features and technical advances which may now make the technique clinically applicable. In addition to amplification and signal averaging, an adjustable input filtration system excludes beats which are unacceptably "noisy" compared to a 4 beat template. Thus, extremely "clean" signals are presented for processing by the average allowing resolution of very low amplitude signals. Clear unequivocal His bundle recordings were obtainable in 25 of 55 patients (45%). A correlation coefficient of +.97 was obtained between invasive and non-invasive HV intervals. The 55% failure rate was attributed to prolonged atrial activity in 31%, short PR in 9%, and technically unsatisfactory recordings with excessive or overwhelming noise which did not allow appreciable signal resolution in 15%.     

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.     

Effects of Sotalol on His-Purkinje Conduction and Refractoriness in Humans

BACKGROUND: The effects of sotalol on refractoriness in human ventricular and atrial muscles have been well established, but the drug's effect on the electrical properties of the His-Purkinje system in humans is not known, especially whether sotalol's effect is due solely to its action on prolonging repolarization or in combination with its beta-blocking properties. We studied the electrophysiologic effects of intravenous sotalol and propranolol in patients undergoing electrophysiologic studies of cardiac arrhythmias. METHODS AND RESULTS: We studied 22 patients (19 men, 3 women; mean age, 60 +/- 6 years) who had coronary artery disease and assessable anterograde, retrograde, or both, His-Purkinje system function. Fifteen patients underwent electrophysiologic studies before and after intravenous sotalol (1.5 mg/kg), and 7 patients underwent electrophysiologic studies before and after intravenous propranolol (0.15 mg/kg). Both sotalol and propranolol had no significant effect on the H-V interval, but sotalol significantly increased ventricular refractoriness and His-Purkinje refractoriness, both in anterograde and retrograde conduction, whereas propranolol did not, Sotalol's effect on His-Purkinge refractoriness also caused atrioventricular block distal to the His bundle during atrial pacing at a moderately fast rate. Sotalol was not effective in preventing bundle branch re-entry tachycardia, nevertheless, it increased cycle length of bundle branch re-entry tachycardia by increasing refractoriness. CONCLUSIONS: Sotalol increased His-Purkinje refractoriness in humans but had no effect on His-Purkinje conduction. The drug must be used judiciously in patients with a diseased His-Purkinje system because it may cause atrioventricular block distal to His at fast heart rates. Sotalol had no effect on macrore-entry utilizing bundle branches.     

In Anterior Myocardial Infarction, Frequency Domain is Better than Time Domain Analysis of the Signal-Averaged ECG for Identifying Patients at Risk for Sustained Ventricular Tachycardia

Low amplitude signals at the end of the QRS in patients with prior myocardial infarction (MI) are related to fragmentation of the electrical impulse in ventricular myocardium and are known to correlate with an increased risk of sustained ventricular tachycardia (VT). We hypothesized that in patients with anterior MI (AMI), earlier activation of the damaged anterior wall would cause an earlier fragmentation of the signal-averaged EGG (SAECG) signal, making conventional time domain analysis of late potentials difficult. We performed SAECG in 213 patients (62 with AMI and 58 with inferior MI [IMI]). Fifty-seven had prior sustained VT; 23 with AMI and 24 with IMI. We examined the standard time domain SAECG parameters including the duration of the filtered QRS (40–250 Hz), the duration of the late QRS < 40 μV, and the root mean square amplitude of the last 40 msec of the QRS. We also examined the power law scaling (PLS) in the frequency domain. Receiver operating characteristic curve analysis of a discriminant function demonstrated significant differences for PLS as compared to time domain indices. An important finding was the significance of MI locus in the time domain indices. PLS did not exhibit this dependence. These data suggest that the usual indices are insufficient for identifying AMI patients at risk of VT. PLS, on the other hand, is valuable regardless of MI location.     

A Method of Esophageal Electrogram Recording for Diagnostic Atrial and Ventricular Pacing

This study evaluates improvement of the electrogram sensed via an esophageal catheter with the sensing electrode adjacent to the stimulating electrode with and without a specialized artifact suppression system. In 100 patients (65 men and 35 women) aged 16-60 years (mean 48 years), esophageal recordings of left atrial activity were obtained during simultaneous transesophageal atrial pacing. Transesophageal ventricular pacing was performed in an additional 34 patients. Without the suppression system, ventricular paced activity, recorded from the esophagus, was not suitable for interpretation. About 10% of the atrial electrogram response could be recorded and evaluated during atrial pacing. With the stimulus artifact suppression system, interpretable recordings were obtained 100% of the time during atrial and ventricular recordings. The method described allows use of transesophageal diagnostic testing where previously only the intracardiac route was possible.