Implanted medical device/external medical instrument communication utilizing surface electrodes

Abstract

A medical device communications system uses subthreshold pulses, modulated to provide relatively high speed electrical communications with inexpensive external devices connectable to a body with the implant by surface leads.

What is claimed is:  
     
         1 . A communications system for use with an implantable medical device, comprising: 
 a pulse generation circuit to deliver a first electrical signal at a first threshold to electrically stimulate body tissue;    a control circuit coupled to the pulse generation circuit, the control circuit to cause the pulse generation circuit to deliver a second signal at a second threshold below the first threshold to prevent substantial physiological effects in response to the second signal, the second signal including encoded data; and    a receiving circuit to receive the second signal, enabling external transfer of the encoded data.    
     
     
         2 . The system of  claim 1 , wherein the second signal is a modulated biphasic pulse.  
     
     
         3 . The system of  claim 2 , wherein the biphasic pulses are delivered during a refractory period.  
     
     
         4 . The system of  claim 2 , wherein the second signal is an amplitude modulated biphasic pulse.  
     
     
         5 . The system of  claim 2 , wherein the second signal is a frequency modulated biphasic pulse.  
     
     
         6 . The system of  claim 2 , wherein the second signal is a pulse-width modulated biphasic pulse.  
     
     
         7 . The system of  claim 6 , wherein the pulse generation circuit includes a circuit to perform pulse train modulation on the second signal.  
     
     
         8 . The system of  claim 6 , wherein the pulse generation circuit includes a circuit to control the polarity of the biphasic pulse.  
     
     
         9 . The system of  claim 1 , further comprising a trigger circuit coupled to the control circuit to receive a trigger signal from outside the body, the control circuit causing the pulse generation circuit to deliver the second signal in response to the trigger signal.  
     
     
         10 . A method of providing communication between an implantable medical device and an external device, comprising the steps of: 
 generating a first electrical signal at a first threshold to electrically stimulate body tissue;    generating a second electrical signal, including encoded data, at a second threshold below the first threshold to prevent physiological effects in response to the second signal; and    sensing the generation of second signal at the external device.    
     
     
         11 . The method of  claim 10 , wherein the second signal corresponds to multiple biphasic pulses.  
     
     
         12 . The method of  claim 11 , wherein the second signal corresponds to modulated biphasic pulses.  
     
     
         13 . The method of  claim 11 , wherein the second signal is delivered at a predetermined time relative to a cardiac cycle of the heart.  
     
     
         14 . The method of  claim 10 , further comprising the step of providing an external signal from outside the body to trigger delivery of the second signal.  
     
     
         15 . The method of  claim 10 , wherein the second signal includes marker channel data.  
     
     
         16 . The method of  claim 10 , wherein the second signal corresponds to patient data.  
     
     
         17 . The method of  claim 10 , wherein the second signal corresponds to device-specific data.  
     
     
         18 . The communications system of  claim 10 , wherein the second electrical pulses are transmitted during segments of time related to one of a sensed cardiac event and a pacing pulse.  
     
     
         19 . The system of  claim 10 , wherein the second signal is transmitted during segments of time related to one of a sensed cardiac event and a pacing pulse.  
     
     
         20 . The method of  claim 10 , wherein the second electrical signal is generated during segments of time related to one of a sensed cardiac event and a pacing pulse.