Simultaneous Atrial and Ventricular Electrogram Transmission Via a Specialized Single Lead System

Simultaneous Atriai and Ventricular Electrogram Transmission Via a Specialized Single Lead System HOWARD C. HUGHES, SEYMOUR FURMAN,* ROBERT R. BROWNLEE,** and CHARLES D E L M A R C O * * From The Milton S. Hershey Medical Center of The Pennsylvania State University, Montefiore Medical Center,* and Cardiac Control Systems**

Transmission simultanee des electrogrammes auriculaire et ventriculaire par une electrode sp^cialisee unique, Aucun stimulateur a (elemetrie n'est capable de detecter et transmettre i'^lectrogramme [EGM] pendant le rythme normal ou stimuJe. Certains peuvent detecter et transmettre soit I'onde P,soit I'onde R. Une nouvelie electrode reJide a un nouveau stimulateur a telemetrie a ete d^velop^e. EJJe permet la transmission de J'EGM complet sans etre affects ni par Je courant du stimuiateur, ni par Jes postpotentieJs. Les electrodes sont placees dans i'oreiJJette et le ventricuJe droit pour optimiser la detection. Ces electrodes sorit separees ^lectriquement des electrodes de stimulation et de recueil du potentie]. Cependant elle/ont partie d'une electrode ventriculaire coaxiale qui n'est pas pJus large qu'une electrode bipoJaire normaie [2,3 mm). Le systeme de tel^metrie est compatible avec Je monitoring par telephone. Ce systeme a pu demontrer sa capacite pour la detection correcte de l'EGM pendant le rythme sinusai normal et n'affecte pas la stimulation auricuJaire, ventricuJaire ou AV sequentieJJe. De pJus, il detecte et transmet des anomalies telies que des extrasystoles, la conduction retrograde et des modifications isch^miques. Les Electrodes de ce type Jiees d des stimulateurs VVI avec teJemetrie ont ete implantees chez des chiens durent plus de 2 ans. Ce systeme fournira les moyens de detecter de fagon non-invasive et d'enregistrer par teJemetrie l'EGM normaJ et anormaJ en entier, meme chez les patients qui dependent de ieur stimuJateur. HUGHES, H.C., ET AL.: Simultaneous atriai and ventricular electrogram transmission via a specialized single lead system. !^o telemetricaJIy monitorabie pacemakers are capabJe of detecting and transmitting the complete eJectrogram (EGM) during normal and paced rhythms, although some are capable 0/ detecting and transmitting either the P- or R-wave. A new lead and teJemetry-pacemaker system has been developed that permits the transmission of the complete EGM and is not adversely affected by pacemaker outputs or a/ter-potentiaJs. Electrodes are placed in the right ventricle and atrium to optimize EGM detection. These A-V data probe electrodes are eJectricaJJy separate from the pacing-sensing electrodes but are structurally part of a coaxial ventricular lead that is no larger than a conventional bipolar lead {2.3 mm). The telemetry system is also compatible with telephone monitoring systems. The system has consistently demonstrated its ability to detect accurately the EGM during normal sinus rhythms and does not affect utriaJ, ventricular, or A-V sequential pacing. In addition, this system can detect and transmit EGM abnormalities, including ectopic beats, retrograde conduction, and ischemia changes. A-V data leads with telemetry monitored VVI pacemakers have been implanted in dogs for over two years. This system will provide the means to detect and telemetrically record noninvasively the entire normalundabnormalEGM, even in pacer dependent patients. [PACE, Vol. 7, November-December, 1984) pacemaker, telemetry alectrogram, leads, electrodes Address for reprints; Howard C. Hughes, V.M.D., Department of Comparative Medicine, The Miiton S. Hershey Medical Center, The Pennsylvania State University, Box 850, Hershey, PA 17033 U S A

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Supported, in part, hy grants from USPHS (ROl HL-13988 and K04 HL-00586) and Cardiac Control Systems.

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Introduction Functional evaluation of cardiac pacemakers is mandatory for the health and well-being of the patient.' Telemetrie monitoring has become more sophisticated as low drain microcircuitry and power supplies have improved. Monitoring of programmed parameters, as well as output voltage, current, and end-of-life indicators, are becoming the rule.'-" The surface electrocardiogram (ECG) must still be relied upon to differentiate normal from abnormal rhythms and to detect abnormal pacemakers. The increased use of dual chamber, so-called universal or pbysiologic pacemakers, has made functional evaluation even more complex.' ^ These pacers produce a wide array of ECG changes wbicb make interpretation of pacer function difficult. Routine monitoring of these pacemakers has progressed from the simple lead II ECG through a minimum of six leads for single chamber to a full 12-lead ECG for dual chamber pacers. Even then, the multiplicity of programmable parameters still produces ECG confusion. Echocardiographs have even been required to aid in determination of capture in more difficult cases."• The purpose of this report is to describe a new electrogram telemetry system which uses an intracardiac lead system to detect the electrogram (EGM). This lead system is an integral part of the ventricular lead and is not adversely affected by pacemaker outputs or afterpotentials.

Figure 1. This is a diagram of a coaxial A-V Data Lead positioned in (he righl heart. The tip is usedforall pacer function while the rings are used for EGM telemetry only.

The lead (A-V Data Lead*) is of the coaxial transvenous ventricular type [Eig. 1]. The central wire is used for the pacing and sensing functions through an 11 mm^ platinum iridium (Pt-Ir) tip. Tbe EGM telemetry functions are performed by two separate Pt-Ir rings (25 mm^) tied electronically in parallel. The rings are positioned along the body of the lead so the tip is 1.0 cm from the tip for R-wave detection, while the proximal ring is positioned in the atrium (8-13 cm from the tip) in close proximity to the S-A node for P-wave detection. Segmented polyether polyurethane (Surethane) is used for insulation.

The A-V Data Lead was passed trahsvenously through the jugular vein in anesthetized (sodium pentobarbital 35 mg/kg) pigs (n = 10) and dogs (n = 15). The tip was positioned in the apex of the right ventricle. In addition, an atriai J-lead was passed through the same vein and its tip was positioned in the right atriai appendage. Operative electrophysiologic studies were done similarly in all animals. An E-for-M* VR-6 recorder was used for the EGM measurements. The EGM for the right ventricle was determined for the tip in the unipolar mode with a 50 cm^ subcutaneous plate as the indifferent. The EGM for the A-V Data Probe was examined separately, also in the unipolar mode. Recordings were made at 50 or 100 mm/s and triggered sweeps were photographed at 250-1000 mm/s pulse durations from 0.1-1.0 ms.** Threshold voltage and currents were

*Cardiac Control Systems, Palm Coast. FL, U.S.A.

*Electronics-for-medicine, Pleasantville, NY, U.S.A.

Materials and Methods

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TRANSMISSION

IMPLANTED PACEMAKER

PACINO/SENSINO

9KtH

PACEMAKER

BATTERY

O A-V OATA ELECTHODES

EXTERNAL COIL

VOLTAQE CONTROLLED OSCILLATOR AMPLIFIER CABE

AMPLIFIER

FREOUENCY TO VOLTAQE CONVERTER

STRIP CHART RECORDER

Figure 2.

This

ic drawing shows the functional components o/ the A-V Data telemetry

system.

determined using an oscilloscope and a customdesigned square wave stimulator. Electrograms were recorded from the A-V Data Probe during atrial, ventricular, and A-V sequential pacing as well as during sinus rhythm. In the chronic studies, the A-V Data Leads were connected to telemetrically monitored VVI and DDD pacemakers following operative electrophysioiogic measurements (Fig. 21.

Results The peak-to-peak amplitudes of the R-wave for the pig (5.9-10.4 mV) were much smaller than those of the dog (24.0-30.0 mV).''^ The R-wave peak-to-peak slew rate of the dog (1.5-3.0 mV/ms) was greater than that of the pig (0.6-1.2 mV/ms). Likewise, pacingthresholdswiththeA-V Data Lead were similar to those values obtained for other unipolar leads with similar configurations.'"^ At 0.5 ms, the threshold for the dog was 0.36 ± 0.23

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volts and 0.60 ± 0.40 mA, and those for the pig were 0.37 ± 0.14 volts and 0.82 ± 0.39 mA. The EGM detected from the A-V Data rings showed that it was similar in configuration to the lead II ECG but had a five to six times greater amplitude (Fig. 3). When compared to the EGM taken separately from the individual atrial and ventricular leads, there was a 25-50% attenuation of the signal. The EGM could not he detected on the lead doing the pacing because of the pacer spike and after-potentials; however, detection of the EGM from the A-V Data Probes was easily visible regardless of pacing site (Fig. 4). In comparison to the ECG, the individual waveforms were more easily recognized. In lead II, the P-waves were often obscured by T-waves and R-waves as atrial depolarization walked through the EGG. The P-wave from the atria! lead EGM often obscured the T-wave during ventricular pacing. With the A-V Data Lead, however, EGM always detected clear distinct individual waveforms (P-, R-, and Twaves).

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Figure 3. The upper tracing is an EGM/roni (he A-V Data Lead (2 mV/cm] and the lower is o lead U ECG (I mV/cm) during normal sinus rhythm.

During atrial pacing, the ventricular tip electrode detected satisfactory R-waves; however, determination of atrial capture hy examination of the ventricular EGM was not always possihle due to the low amplitude of the far-field P-wave. With the A-V Data Lead, there was excellent differen-

tiation of all waveforms. Pacer artifacts were clear and P-waves were distinct. Measurements of stimulus to P-wave and P-R intervals could he made accurately. The EGM from hoth the atrial and ventricular tip leads were not detectahle during pacing due to the relatively high amplitude of the

Figure 4. During ventricular pacing, (he ventricular EGM is obscured. The upper trace shows an atriai EGM (5 mV/cm], the middle, A-V Data EGM (5 mV/cm) and the lower is a lead 11 EGG (1 mV/cm). In the second paced complex, (he T-wave is obscured by the P-wave in the atriai EGM and the T-wave is obscured by the P-wove in lead U. The A-V Data Lead shows all waveforms. 1198

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Figure 5. All waveforms are readily apparent during sequential pacing when the A-V Data Lead is used for EGM detection [250 mm/s; 2 mV/cm). output spikes and after-potentials. With the A-V Data Lead, P-, R-, and T-waves were readily detectahle following the pacemaker stimuli, as were the other electrophysioiogic parameters that are normally measured (Fig. 5). In the pig, ventriculoatria) (VA) conduction al-

ways occurred during right ventricular pacing. Figure 6 shows telemetered tracings from the A-V Data Lead during normal sinus (upper) and ventricular pacing. All waveforms during normal sinus and paced rhythms could be easily identified. Retrograde P-waves occurred 178 ± 8 ms after ventricular stimulation as compared to antegrade conduction times of 120 ± 18 ms. In the chronic dogs studies, A-V Data Leads have been functioning with telemetry units for over two years. Simply hy placing an external telemetry coil in the vicinity of the internal telemetry system, intrinsic and paced intracardiac EGMs were easily detectable (Fig. 2). P-, R-, and T-waves, premature heats, arrhythmias, and EGM intervals were all easily identifiable. In one animal that had previous chest surgery, myocarditis and its associated arrhythmias were detected with this system before obvious clinical signs had occurred. There have heen no lead or telemetry-related failures. The SPU lead coating gives strength and flexibility to the lead.'" The modulus of elongation (> 700%) and strength (> 6000 psi) of SPU are superior to silicone (< 500% at 1200 psi) and urethane (< 400% at 6000 psi). Long-term transven-

Figure 6. The upper A-V Data telemetered tracing from a pig during normal sinus rhythm. The lower shows the development of retrograde conduction during ventricular pacing. PACE. Vol. 7

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HUGHES, ET AL. ous leads (up to 30 months) have heen implanted in dogs without adverse effects. Light and scanning photomicrographs show a freedom from cracks, crazing, and internal/external wear defects after over a cumulative 300-month implant experience. Polarized light has failed to show any stress-related defects in this SPU coating. Discussion Advances in telemetric monitoring make it possible to examine many pacemaker functions including rate, output current and voltage, pulse width, pacing energy, battery voltage, lead and battery impedance, sensing margin, etc. after implantation:''-'^ however, the one highly critical factor that cannot presently he telemetrically monitored is the intracardiac electrogram (EGM). The ability of pacing electrodes to sense and detect normal intrinsic cardiac electrical activity is not in question. These electrodes are adequate for the detection of the normal non-paced EGM. Telemetry systems incorporating such systems have seen some limited use.^ They cannot, however, be used to detect the EGM immediately following a stimuli originating from that electrode. The pacer output, after-potential, and electrode-tissue polarizations render the electrode hlind to the induced EGM. Furthermore, since the sensing circuit gain is tuned for the relatively low voltages of the heart (3-4 mV for the atrium; 10-20 mV for the ventricle), the thousand-fold higher output levels produced by the pacemaker must be blocked from the sensing circuit in a way somewhat analogous to darkadapted eyes being suddenly blinded by a very bright light. Without protection temporary blindness will occur. This is accomplished by including blanking and refractory periods in the pacer so that it is not disabled by its own electrical activity and to prevent cross-talk between atrial and ventricular pacing functions. Therefore, it is not possihle even to try to determine a capture EGM until long after the intrinsic waveform has moved well away from the pacing electrode. A system which uses the same electrode for pacing, sensing, and telemetry may only function when the pacemaker is not

pacing. This negates the use of such a one-electrode telemetry-pacing system in all single chamher and any dual chamber pacers in which both chambers may be paced (DDD). The use of separate electrodes for the detection of the EGM have been previously proposed."'' This system was capable of detecting the EGM during both intrinsic and paced beats, but it lacked the ability for high resolution EGM detection from both chambers simultaneously. The A-V Data Probe functions are completely separate and independent of all pacemaker functions; the lead is capable of high resolution EGM detection during all phases of the cardiac cycle. Two separate rings are electrically tied together and are placed for optimum EGM detection. Some cancellation of the signal, primarily the R-wave, does occur due to electrode loading and detection of far-field signals on the ring in the nonactive chamber. This resulted in the 25-50% reduction in R-wave amplitude as compared with a single ring. The size (< 2,3 mm) and handling characteristics of the A-V Data Lead are similar to those of the standard bipolar leads. The polyurethane (CGS/Urethane) assures longterm hiocompatihility and stability. When the lead is combined with a high resolution telemetry system, detection and transmission of the entire EGM from hoth chambers of the heart is possihle. The pacing and intrinsic EGMs from single or dual chamber pacemakers are equally as clear and straightforward. The pacer output spikes are clear and these are followed by distinct P- or R-waves (Fig. 5). The T-wave and P-waves are not obscured by pacing or other electrical events occurring in the other chamber (Fig. 4). Gapture, retrograde conduction, fusion, pseudofusion, and non-capture are all readily identified. Measurement of all electrophysiological intervals is possible. This low-drain telemetry monitorahle pacing system will add significantly to the long-term care and diagnostic ease in the pacemaker patient. Glear, concise EGM recordings will be available by transtelephonic monitoring systems (Fig. 2). The potential for long-term continuous Holter-type monitoring of intracardiac electrical activity is also provided by this system.

References 1. Levine, P.A., Belott, P.H., Bilitch, M., et al.: Recommendations of the NASPE policy conference on 1200

pacemaker programmability and follow-up. PAGE 6:1222, 1983.

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Barold, S.S., Falkoff, M.D., Ong. L.S.. et al.: Interpretation of electrocardiograms produced by a new unipolar multiprogrammable "committed" A-V sequential demand (DVI) pulse generator. PAGE. 4:692. 1981. Levine,P.A.,Brodsky, S.]., Seltzer, J.P.: Assessment of atrial capture in committed atrioventricular sequential (DVI) pacing systems. PACE, 6:616,1983. Hughes, H.C., Tyers, C.F.O.: Effect of stimulation site on ventricular threshold in dogs with complete heart block. Am. Heart /., 89:68, 1975. Hughes, H.C., Brownlee, R.R.: An A-V data lead system for electrogram detection. In K. Steinbach (Ed.): Cardiac Pacing, Proc. Vllth World Symposium on Gardiac Pacing, Steinkoff-Verlag, Darmstat. 1983, p. 409. Bowman. T.A., Hughes, H.C.: Swine as in vivo model for electrophysioiogic evaluation of cardiac pacing parameters. PACE, 7:187, 1984. Lathrop, T.: Medtronic's Spectrax-SXT and the intracardiac electrogram. Medtronic News, 11:20, 1981. Hughes, H.C.. Brownlee R.R., Tyers, G.F.O.: Failure of demand pacing with small surface area electrodes. CircuJafion, 54:128, 1976.

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9. Hughes. H.C., Brownlee, R.R., Bertolet. R.D.: The effects of electrode position on the detection of the transvenous cardiac electrogram. PACE. 3:651,1980. 10. Hughes, H.C., Bertolet, R.D., Kissinger, J.T,: A new polyurethane and process for pacer leads. In K. Steinbach (Ed,): Cardiac Pacing, Proc. Vllth World Symposium on Cardiac Pacing, Steinkoff-Verlag, Darmstat. 1983, p. 23. 11. Brownlee, R.R.. Hughes, H.C., Tyers. G.F.O., et ai.: Monitoring systems for cardiac pacemakers, Trans. Am. Soc. Artif. Inter. Organs. 23:65, 1977. 12. DelMarco. C.J., Tyers. G.FO., Brownlee. R.R.: Lithium pacers with self-contained multiparameter telemetry: First year follow-up. In C. Meere (Ed.): Proc. Vlth World Symposium on Cardiac Pacing. PACE SVMP., Montreal 1979: Chapter 28, Section 1. 13. Gorman, I.M., O'Neill, M.J.. Tyers, G.F.O., et al.: A preliminary report on telemetric monitoring of pacemaker electrode impedance. In C. Meere (Ed.): Proc. Vlth World Symposium on Cardiac Pacing. PACE SVMP., Montreal 1979: Chapter 28, Section 4.

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