CA1074872A - Command atrial cardioverter - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An externally controlled implantable electronic device for delivering a cardioverting pulse of energy to the atrium of an ailing heart is provided. The device is adapted to be activated only upon the manual intervention of an operator, who may be the wearer, when it is desired to effect atrail defibrillation. A receiver is arranged to receive commands from outside the skin and activate the device. A charging circuit delivers to a storage circuit an amount of energy sufficient to convert an abnormal supra-ventricular rhythm to a normal sinus rhythm. A controllable switch causes this energy to be discharged into the atrium through delivery electrodes to effect defibrillation.

Description

`" ~074~372 There are individuals walking the streets today who experience recurring episodes of atrial fibrillation, atrial flutter, or tachycardia. While not life-threatening, these supra-ventricular arrhythmias can become debilitating and lead to comp-lications, and hence require trea-~nent when present. Such indi-viduals require frequent electrical or pharmacological conversion under the care of the physicians to return their hearts to normal sinus rhythm.
Drug therapy is frequently successful in correcting atrial fibrillation, flutter or tachycardia, but there are many patients who are resistant to the appropriate drugs or who suffer serious side-effects from the drugs. For these patients, cardio-version is accomplished by way of a technique in which a pulse generator and external paddles combine to send high energy elec-trical pulses through the ailing patientls thorax to the heart.
For those who suffer from recurring bouts of atrial tachyarrythmias, regular and often times frequent visits to hos-pitals are in order. Those whose hearts can be successfully re-turned to normal sinus rhythm by way of drug therapy frequently undergo hospitalization so that the effects of the administered drugs can be carefully monitored. Similarly, those requiring electrical cardioversion are generally cardioverted in the hos- ., .
pital due to the fact that the procedure frequently required the application of a general anesthetic and carries with it a sig-nificant risk to the patient.
It is toward the facilitation of treatment for and the , reduction of the risks to those patients suffering from recurring episodes of atrial fibrillation, flutter and tachycardla, that the present invention is directed.
The present invention relates to an atrial cardioverter designed to be implanted under the skin of patients who frequentl~
suffer from bouts of atrial fibrillation, flutter or tachycardia.

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During those times when the patient is suffering such an arrhyth-mia, and cardioversion is in order, a command given by the patient or his physician brings the inventive cardioverter out of its standby condition to administer a low-level pulse of energy directly to the heart, for example, through a catheter implanted in or about the atrium. Cardioversion by means of an electrical discharge delivered through an intra-atrial catheter has been shown to require energies of five watt-seconds or less, and is thus a painless procedure not requiring anesthesia.
In one embodiment of the present invention, the patient will likely visit the office of his physician for treatment. By way of an external console, the physician programs the desired level of cardioverting energy to be administered. Then, both the power to charge an implanted discharge capacitor and a set of control signals corresponding to the programmed level of cardio~
verting energy is transmitted through the skin of the patient ., .:
and into the implanted unit. In addition, the invention contem-plates that an ECG synchronization signal be derived either inter-nally or from an external ECG unit and fed back -through the skin of the patient as a command signal to ensure that cardioversion occurs in proper synchronization with the QRS complex. With the present invention, provision can be made to discharge the stored energy through a test load for verifying the readiness of the implanted unit, and information can be extracted through the skin of the patient so that the physician is able to monitor the dis-charge of the implanted capacitor, which is either through the test load or the implanted atrial catheter.
In another embodiment of the present invention, the patient is able to cardiovert himself at home, without the inter~
~ention of his physician. The patient who frequently undergoes attacks of atrial fibrillation, flutter or tachycardia can be taught to recognize the symptoms of such arrhythmias. Once able ; .

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to recognize that he or she is experiencing such an attack of a convertible arrhythmia, the patient can effect cardioversion when appropriate.
In the second patient-operated embodiment o~ thepresent invention, an ener~y source is incorporat~d into the implanted cardloverting device. The energy source is normally maintained out of the cardioverting circuit, and is connected into the cir-cuit only upon the issuance of an appropriate command. As here disclosed, the patient issues this command by holding a magnet at an appropriate location against his skin, and a reed switch closes. Upon ~he closing of the reed switch, the energy source is brought into the circuit, and the discharge cycle is initiated.
In the embodiment of the present invention designed for operation by a physician, the level of cardioverting energy to be delivered to the patient can be manually programmed. In the embodiment of the invention designed for operation without the : j . :
intervention of a physician, it is also possible to deliver the cardioverting shocks in varied energy levels. In this regard, the patient-operated embodiment of the invention contemplates sequentiall~ increasing the cardioverting energy level over prior attempts at cardioversion. The patient controls repeated dis-charges by way o the duration of magnet placement against his skin.
Like the first, the second embodimen-t of thepresent invention can be equipped with circuitry for synchronizing the cardioverting shocks with the QRS complex. This can be accomp-lished by way of a sensing probe positioned in or about the heart.
A major object of the present invention is to provide an implanted e~ternally operated device which will efficiently cardiovert a heart under~oing atrial fibrillation, flutter or tachycardia, comfortably, without the necessity for administration ~07~7Z

of an anesthetic, and without the necessity of physician inter-vention.
Another major object of the present invention is to provide an implanted cardioverter whose operation can be verified before the discharge of electrical energy into the heart.
These and other important objects of the present inven-tion will become more apparent when reference is made to the following description taken in conjunction with the accompanying drawlngs .
~igure 1 is a block diagram of an embodiment of the inventive implantable command cardioverter particularly suited for use in the office of a physician;
Figure 2 pictorially depicts the physician's console which is represented in Figure l as associating with the inventive implantable cardioverter; and Fiyure 3 is a block diagram of another embodiment of the inventive implantable command cardioverter, suitable for operation without the intervention of a physician.
~ ith reference initially to Figures 1 and 2, the first embodiment of the present invention will be described. The inven-tive implantable command cardioverter is indicated generally at 10 and is adapted to associate with an external console generally designated at 12. Console 12 includes circuitry for transmitting power and control lnformation to the implanted cardioverter for receiving information about the nature of the cardioverting pulses from the implanted cardioverter as well as signals from other cardiac equipment, and for visually displaying selected cardiac in~ormation. The numeral 14 schematically represents the skin of ; the patient, and hence shows the separation ~etween the implanted cardioverter lO and the external console 12.
The console 12 comprises a power and information trans-mitter 16 which communicates with an implanted receiver unit l~.

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Information such as the desired cardioverting energy, whether the unit should be in its "test" or its operating mode, etc., all of which will be explained below, is programmed into an operating control unit 20. Unit 20 may, for example, include a plurality o~ on-of switches which generate digital signals. The digital signals from operating control unit 20 are i-ed in parallel to an information modulator circuit 22 where they are converted into a serial chain of operating commands.
Schematically illustrated in Figure 1 at 24 is an ECG
input which may be in the form of a conventional ECG unit or an amplifier which is made an integral part of the console 12. A
sequence of electrocardiograph s-ignals taken from the skin 14 of the patient is further illustrated at ~ in Figure 2. From the electrocardiograph input 24 can be derived impulses which are representative of the occurrence of the QRS complex. The QRS
impulses are fed to the information modulator 22 as is schemati-cally represented, from the ECG synchronization unit 26.
Also part of the external console 12 is a receiver and decoder 28 which is adapted to receive and decode information transmitted by the implanted transmitter 30. After being decoded, the information delivered across the skin 1~ by transmitter 30 is `
displayed at an external display unit 32. As can be seen, the implantea transmitter 30 sends signals across the skin 14 of the patient to *he--receive~ and decoder 28 much the same as-external transmitter 16 sends signals to 1mplanted receiver 18. Of course, the particular form of modulation couid be different.
As represented in Figure 1, power and information sig-nals are transmitted through the skin of the patient by way of coupled transformer primary and secondary windings. In the specific physician-controlled embodiment herein illustrated and described, power to the implanted unit and the control information is, for simplicity, transmitted along the same channel. The ~i7~i72 control information can be modulated into the power channel by ~requency shift keying, pulse width modulation, or any other appropriate well-known modulation technique.
With specific reference to Figure 2, the external con~
sole 12 can he seen to include a display portion 32 and an operat~
ing control panel generally designated at 20. Control panel 20 is.equipped with an on/off switch 34, an input for the ECGsignal 24, ~:
a rotary energy dischàrge dial 36 to enable the physician to control the amount of energy discharged into the heart, a toggle switch 3~ for controlling whether the stored energy is discharged into a test load or into the heart, a push button 40 to initiate the discharge of the implanted storage capacitor, and a load-data push button 41. Also illustrated as part of the display portion of external console 12 is a cathode ray tube 42 shown as simultaneously displaying the periodic QRS complex 4~ and, in broken lines, the discharge of the implanted storage capacitor.
~ ith continuing reference to Figures l and 2, the opera- :
tion of the external unit will be described. The patient suffer-ing ~rom a convertable atrial arrythmia, such as atrial ~ibrilla-tion, ~lutter or tachycardia, is e~amined by the physician, pre-ferably with the aid of ECG e~uipment. Based upon this input, . the physician makes his best estimate o~ the energy level which will be required to cardiovert the malfunctioning heart, and sets rotary dial 36 accordingly. The ECG synchronization input is then connected to ~he console 12, the toggle switch 3~ is set to either . the test load or catheter discharge position, and toggle 34 is moved to the `'oni' position. ~t this time, the unit is functional, with energy being transmitted to the implanted circuitry, and with EC~ signals being displayed on the display device 32 as shown at 4~. The physician then presses the load-data button 4:L to trans-mit the instructions regarding the level of the dischaxge pulse to the implanted unit at which time the energy storage capacitor : , ~
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is charged to the desired level. When ready, the "discharge"
button 40 is depressed, and either the test load or the heart is shocked at the proper time during the QRS complex. The test load is, of course, intended to verify attaining the proper level of discharge before a shock is actually appliecl to the heart. ~hen the discharge level is verified, the physician simply moves switch 38 to the catheter position, presses the load-data button and then the "discharge" button 40 to deliver a pulse to the heart.
Once a shock is actually applied to the heart, the physician ob-serves the screen of CRT 42, and either concludes his activity ifcardioversion is successful, or repeats the cardioverting attempt at perhaps a higher energy level if unsuccessful.
When the rotary energy dial 38 and the other controls are set by the physician, the operating con-trol unit 20 provides, ~or example, a binary signal representative of the energy level to which the dial 36 is set and other operating parameters. This signal takes the form of a parallel binary contro~ woxd. As noted above, the rotary dial 36 could be replaced by a set of toggle switches, each one of which would provide a discrete binary con-trol signal. The parallel binary control word from the operatingcontrol unit 20, as illustrated in Figure 1, is delivered to the information modulator 22 where it is converted into a serial binary control word. From modulator 22, the serial control word is del-ivered to the transmitter 16 and sent tothe implanted device along the information channel. Simultaneously, the ECG synchronization signal is delivered to the modulator 22.
~ hen the on/off switch 3~ on the external console 12 is in the "on" position, the transmitter 16 is activated, and energy ; in the for~ of power signals is transformer coupled across the ~ `0 skin of the patient. This energy is received through the secondary .~ .
winding of the ~oupling transformer at receiver 18. Then, when the load-data button 41 is depressed, the serial binar~ control ' . . .
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word i5 transmitted along the information channel. The serial control word recovered by the receiver 18 ta]ces the form of a timed set of pulses. The receiver 18 directs these serial pulses to a control register 48 which reconstructs them into their original parallel format. The parallel control word, along with other control information, provides a signal proportional to the desired energy level which is then transmitted via discrete lines 50 to circuitry associated with a power inverter 52.
Before the activity of the power inverter 52 is initi-ated, the control register 48 issues a "go" signal which confirms receipt of the control word from the receiver 18. This may be accomplished in any of several well-known ways, for example, by ending each control word with a unique character to designate its end. This "go" command is indicated at 54. As represented in Figure 1, with three energy control lines 50, a maximum of eight power levels can be set, as a binary format is used. The specific operation of the power inverter 52 and the associated circuitry which serves the purpose of charging the storage capacitor at a predetermined energy level, will be explained below.
The receiver 18 also feeds to the control register 48, information related to the QRS synchronization and whether the energy storage device is to be discharged into the implanted catheter or into a test load. As seen in Figure 1, the synchroni-~ zation signal is carried along lead 56 while the test-mode signal ; is directed along lead 58. The signal on line 58 is fed to arelay driver 60 ~hich associates with coil 62 and in turn, a switch 64. In one position of the switch 64, indicated a~ 66, energy is directed into a test load 68. In the other positio~, designated70 the discharge capaci-tor feeds directly to a cathetex 72 implanted i~ or about the atrium 74 o~ a heart 76.
~hen activated, the power inverter 52 directs energy to an energy storage and discharge device 78 which in this case takes _ g _ . . : ~ . , , . :
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the form of a storage capacitor. ~hen the energy stored by the capacitor 78 reaches the level set on the rotary dial 36, as will be fully explained below, a "ready" signal is produced by a com-parator 100 and fed via line 80 to an AND gate 82. ~he same "ready" signal is also fed bac~ to the power inverter 52.
The "ready" signal which is produced by the comparator 100 is indicative of the discharge capacitor being in readiness for firing through a discharge switch 84. Synchronization signals are at this time, fed to the AND gate 82 along with the "ready"
signal on line 80, and upon the simultaneous occurrence of a "ready" signal on line 80 and a QRS synchronization pulse on line 56, AND gate 82 responds by issuing a signal which controls the state of switch 84, and firing the capacitor 78 through the dis-charge switch. The position of switch 64 determines whether the capacitor 78 fires thro~lgh the test load 68 or through the catheter 72.
The capacitor 78 is charged as explained below. When the control register 48 produces the "go" signal at line 54, this signal reaches a gate input of the power inverter 52. Power in-verter 52 can be of any conventional inverter design which pro-duces an output some~here on the order of 600 volts and can be gated "on" and "o~f" by the application of ex-ternal gating com-mands. The "go" signal from the control register 48 gates -the power inverter 52 on, and the relatively constant 600 volt output , is thereby initiated. The output of the power inverter 52 is fed ` dixectly to the capacitor 78.
As can be seen, a resistive divider in the form of a pair of resistors 102 and 10~ is connected across capacitor 78, and the signal appearing at the junction between the resistors 102 and lQ4 is tapped into one input terminal 106 of comparator 100. The "energy control" command which is produced a~ the con-trol re~ister 4~ and fed alon~ lines 50 forms the input to a . -- 10 - :
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~)7~72 digital-to-analog converter 108. The converter 108 is o~ conven-tional design, with its analog output being directed to the other input terminalllO of compara-tor 100~
When the voltage across capacitor 78 reaches the preset desired level, the signal reaching the input 106 of comparator 100 balances the control signal at input 110. At this time, the comparator 100 produces a "ready~' signal which is simultaneously transmitted to AND gate 8~ along line 80 and to power inverter 52 along ~eedback path 112. The "ready" signal on llne 112 gates the power inverter 52 into its off state. At this point in time, the capacitor 78 is fully charged and in readiness for discharging into either the test load or the heart, and hence the charging operation is completed.
As noted previously, the present invention contemplates an implanted transmitter 30 associated with the receiver and de-coder 28 forming a part of the external console 12. The discharge of the capacitor 78 through either the test load 68 or the cathe-ter 72 is monitored at line 86 which directs a pulse representa-tive of the discharge to a pulse modulator 88. The pulse modula-tor feeds a modulated signal to transmitter 30 which, in turn,transformer couples the signal across the skin 14 of the patient and to the ex~ernal receiver and decoder 28. After decoding, the signal representative of the delivery of an electrical shock is displayed on the CRT as at 46 in Figure 2.
Now, with reference to Figure 3, the totally implantable embodiment of the inventive elective atrial cardioverter will be -described. For convenience of description, those elements which have previously been described with reference to Figure 1 are similarly numbered in Figure 3, and will not again be described 3~ in detail.
In the embodiment illustrated in Figure 3, each element of the inventive cardioverter is implanted beneath the skin 1~ of ... . .. , ,. . . . : .

the patient with the exception of a command magnet 112. Here, the patient controls the operation of the implanted cardioverter by pOSitioning the command magnet 112 at a location on his body immediately opposite an impla~ted reed switch 114. When so posi-tioned, reed switch 114 closes, and the imp:lanted cardioverter is activated.
The fully implanted cardioverter is generally shown in Figure 3 at 10'. After the reed switch 114 closes, a timer 116 . .... .
is turned on and, after a preset delay set into the timer, a switch 118 is closed to direct energy from an implanted battery 120 to the input of. the power inverter 52. Simultaneous with the closing of the reed switch 114, a "clear" signal is issued along line 122 and is ~ed to a binary counter 124 to reset the same to its initial.state. .I~ should of course be appreciated that clo-sure of the reed switch 114 also delivers operating power to the timer 116 and to the binary counter 124, but such connections have been eliminated to simplify the block diagram of Figure 3.
As is evident from Figure 3, an ECG signal is derived by ; way of a catheter 126 implanted in or about the heart, as in the :
right ventricle 128. This ECG signal is further developed ~t ECG
circuitry 130, and synchronization pulses are in turn produced at a QRS synchronization circuit 132. As before, the "ready" signal .
from the inverter-capacitor circuit and -the synchronization signal from the QRS synchronization circuit 132 are both fed to an AND ~-.
gate 82. Upon coincidence of the "ready" and synchronization signals, AND gate 82 switches the discharge switch 84 to its con-ductive state,. thereby discharging the storage and discharge capa-citor 78 through the heart 76 by way of a catheter 72 implanted in :
or about the heart, as in the right atrium 74.
- 30 The operation of the circuit illustrated in Figure 3 is .
as follows. When the knowledgeable patient expexiences either .atrial fibrillation, flutter or tachycardia, and elects to undergo ';

cardioversion, he places the command magnet 112 at the appropriate location near the reed switch 114. The magnetic pull closes the reed switch 114, clears the binary counter 124, and places the timer 116 in its counting state. After a preset delay, timer 116 produces a command which places switch 118 in its conductive state and hence energy is delivered from the source 120 to the power inverter 52.
Once being clearedt binary counter 124 takes its first state which commands power inverter 52 to charge the discharge capacitor 78 to its lowest predetermined energy level. This is accomplished by the binary counter 124 developing an energy con-trol signal, and feeding the same to the power inverter 52 along lines 50. In the same manner as explained above, when discharge capacitor 7~ reaches the proper level of charging, a "ready" sig-nal is issued and is passed to AND gate 82 via line 80. At the same time, the ventricular catheter 126 or another appropriate sensing lead senses the heart function, and a set of QRS synchroni-zation pulses is produced by circuit 132 and fed to AND yate 82 via line 56.
Upon the simultaneous occurrence of a "ready" signal and a QRS pulse, AND gate 82 switches discharge switch 84 to its con-ductive state and the discharge capacitor 78 discharges through the heart 76 of the patient via atrial catheter 72~ Firing of capacitor 78 through the atrial catheter 72 issues a signal at line 134 which sets binary counter 124 to its second state. At the same time, the delay period of timer 116 is reinitiated to enable the patient to assess the effect of the first pulse.
If the patient successfully undergoes cardioversion, the command magnet 112 is removed, and the procedure is completed. If however, after the elapse of the time delay set in timer 116, the patient determines that his heart is still in fibrillation, or undergoing flutter or tachycardia, another cardioversion will be . .

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attempted. With the inventive circuit, this second attempt is at a higher energy level.
After deciding that a second attempt at cardioversion is appropriate, the patient maintains command magnet 112 in its position opposite reed switch 114. As such, there is no "clear"
signal lssued to binary counter 124, and counter 124 remains in its second state after being advanced by the ~irst discharge of the capacitor 7~ through the heart. ~he preset delay in timer 116 elaps~sr and switch 118 is placed in its conductive state.
Therefore, energy source 120 again energizes power inverter 52.
Binary counter 124 then being in its second state, commands power inverter 52 to charge energy storage and discharge capacitor 78 to a higher level of energy. When capacitor 78 reaches this high-er energy level, the capacitor is again discharged through the heart in proper synchronization with the QRS complex. This stepped discharge through the heart can be programmed, as desired by presetting the number of stages of the binary counter 124.
It should be appreciated that as shown in the embodiment illustrated in Fi~ure 3, the QRS synchronization signal can be ~20 taken internally, as, for example, from a catheter implanted in the ventricle. Such an arrangement can also be used in the device of Figure 1 in lieu of the external ECG console. Further-more, while the specific embodiment of Figure 3 employs a multi-stage discharge in increasing-energy levelsj such is not necessary -~-in the basic design of the implantable cardioverter. Rather, the :
binary counter and associated circuitry can be elimina-ted, and the power inverter 52 set so that the first discharge through the heart is at a level sufficient to cardiovert the heart under most condi~ions of fibrillation, flutter and tachycardia.
While specific embodiments of the present invention have been described, it should be understood -that these embodiments are described for purposes of illustration only.

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Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An implantable atrial cardioverter adapted to be activated solely by the manual intervention of an operator from outside the skin of the wearer when it is desired to effect atrial defibrillation, the cardioverter comprising: storage means for storing an amount of energy sufficient to convert an abnormal supra-ventricular cardiac rhythm to normal sinus rhythm; delivery electrode means for associating said storage means with the atrium of the wearer and for discharging the stored energy into the atrium; charging means for delivering to said storage means said amount of energy sufficient to convert such abnormal supra-ventricular cardiac rhythm; receiver means for receiving commands from the operator outside the skin of the wearer to activate the cardioverter when it is desired to effect said defibrillation;
means for initiating the discharge of cardioverting energy into the atrium of the wearer; and means responsive to synchronization signals derived from the QRS complex of the wearer's heart to control said discharge initiating means; said discharge initiating means being responsive to such commands and to said synchronization signals derived from the QRS complex of the wearer.

2. The cardioverter of claim 1, wherein said receiver means is adapted to receive from external to the skin of the wearer, a control signal which determines the amount of energy which said charging means delivers to said storage means; and further comprising means for limiting the amount of energy which said charging means delivers to said storage means in accordance with said control signal.

3. The cardioverter of claim 2, wherein said receiver means is adapted to further receive a power signal from external to the skin of the wearer; and further comprising means for utilizing said power signal as the electrical power necessary for the operation of the implantable atrial cardioverter.

4. The cardioverter of claim 3, wherein said control and power signals are delivered to said receiver across the same channel.

5. The cardioverter of claim 1, and further comprising an implantable test load; load switching means to alternatively associate said storage means with said delivery electrode means or said test load; and means for monitoring the operation of the implantable cardioverter when the stored energy is discharged into said test load; and wherein said receiver means receives switching signals from external to the skin of the wearer which controls the operation of said load switching.

6. The cardioverter of claim 1, wherein said receiver is transformer-coupled to a transmitter through the skin of the wearer.

7. A cardioverter of claim 1, and further comprising means for increasing the amount of energy stored by said storage means for successive discharges of the stored energy into the atrium of the wearer.

8. The cardioverter of claim 7, wherein said receiver means comprises a switch adapted to be closed remotely by the operator from outside the skin to activate the cardioverter, timing means are provided to cause said successive discharges to take place at predetermined periods while said switch remains closed, and said increasing means are arranged to increase stepwise said amount of energy in said successive discharges each time said switch is closed, said increasing means being arranged to be reset when said switch is opened and reclosed.

9. The cardioverter of claim 8, wherein said switch is in the form of a reed switch arranged to be closed by a magnet held by the operator outside the skin.

10. The cardioverter of claim 8, wherein said increasing means includes a binary counter which is advanced by each said successive discharge, and which is reset upon closure of said switch.

11. The cardioverter of claim 10, further comprising means for deriving said QRS complex synchronization signals forming part of said implantable cardioverter.

12. The cardioverter of claim 4, further comprising control means for receiving the control signal from the receiver means and controlling the operation of the carioverter, said control means being in the form of a register adapted to transform serial pulses forming said control signal into a parallel control word, and a digital-analogue converter for converting at least some of the bits of said control word into an analogue signal for controlling the operation of the storage means and determining the amount of energy in the discharge.

13. The cardioverter of claim 12, wherein one of the bits of said control word determines whther the discharge takes place into the atrium through the delivery electrodes or into a dummy load, and another of said bits provides a said synchron-ization signal from said cardioverter which is derived from said QRS complex outside the skin of the wearer.