Abstract: A plurality of electrodes are positioned at the distal end of a catheter such that the electrodes may be positioned proximal biological tissue. A select number of the electrodes have a temperature sensing device associated with them for providing a temperature signal indicative of the temperature at the interface between the electrode and the tissue. A generator operates under the control of a processor to apply power to each of the electrodes. The power has an associated phase angle and, within a time duration, a plurality of alternating on periods and off periods, one set of adjacent on and off periods defining a duty cycle. The processor is programmed to determine the temperature at the electrode/tissue interface based on the temperature signals, compare the temperature to a target temperature and to adjust the power to the electrode accordingly.

Abstract: A pulse having a high-frequency cyclic waveform with a plurality of cycle groups is applied across a defribrillating heart. The waveform has, during the first cycle group, an initial peak-to-peak voltage and, during each subsequent cycle group, a peak-to-peak voltage that may be substantially equal to or less than that of the previous cycle group. In one application, the subsequent cycle groups have progressively decreasing peak-to-peak voltages and the profile of the cyclic waveform resembles a discharge curve of a capacitor. In another the subsequent cycle groups have substantially equal peak-to-peak voltages and the cyclic waveform has a substantially constant peak-to-peak amplitude throughout the duration of the pulse. The waveform of the pulse has substantially no dc component. The total energy delivered to the heart is controlled by adjusting the initial and subsequent peak-to-peak voltages and by varying the time duration of the pulse.

Abstract: A plurality of electrodes are positioned at the distal end of a catheter such that the electrodes may be positioned proximal biological tissue. A select number of the electrodes have a temperature sensing device associated with them for providing a temperature signal indicative of the temperature at the interface between the electrode and the tissue. A generator operates under the control of a processor to apply power to each of the electrodes. The power has an associated phase angle and, within a time duration, a plurality of alternating on periods and off periods, one set of adjacent on and off periods defining a duty cycle. The processor is programmed to determine the temperature at the electrode/tissue interface based on the temperature signals, compare the temperature to a target temperature and to adjust the power to the electrode accordingly.

Abstract: The efficacy of a lesion produced between a pair of ablation electrodes is assessed by analyzing the time it takes for a pulse of energy to travel from one electrode to the other. During a first time period, a first pulse of energy is applied to a first electrode. The time it takes for the pulse to conduct through the tissue to a second electrode is determined. During a time period subsequent to the first time, a subsequent pulse of energy is applied to the first electrode and the time it takes for the subsequent pulse to conduct through the tissue to the second electrode is determined. Changes in the conduction times are monitored by calculating the difference between consecutive conduction times and comparing the difference to a preset value. If the difference is below the preset value the lesion is considered adequate.

Abstract: An apparatus for delivering energy to a biological site includes an electrode device having a plurality of electrodes, the electrode device positioned proximal the biological site. A power control system supplies power having a controllable phase angle to each of the electrodes. A backplate is also positioned proximal the biological site so that the biological site is interposed between the electrode device and the backplate. The backplate is maintained at the reference voltage level in relation to the power. The power control system controls the phase angle of the power so that the current flow between the electrodes and between the electrodes and the backplate results in the continuity and depth of lesions desired. In a preferred embodiment, the electrodes are arranged in a substantially linear array.

Abstract: An apparatus for delivering energy to a biological site includes a catheter having a plurality of electrodes positioned proximal the biological site. A power control system supplies power to each electrode. Where an electrode or group of electrodes is turned off, the power control system provides a high impedance to the turned off electrodes so that substantially no current flows to those electrodes from other electrodes that may remain on. This permits the electrodes turned off to cool. The power control system may permit control over the phase and duty cycle of the power applied to the electrodes and may permit individual control over the power provided to each electrode. A backplate is also positioned proximal the biological site so that the biological site is interposed between the electrodes and the backplate.

Abstract: A plurality of electrodes are positioned at the distal end of a catheter such that the electrodes may be positioned proximal biological tissue. A select number of the electrodes have a temperature sensing device associated with them for providing a temperature signal indicative of the temperature at the interface between the electrode and the tissue. A generator operates under the control of a processor to apply power to each of the electrodes. The power has an associated phase angle and, within a time duration, a plurality of alternating on periods and off periods, one set of adjacent on and off periods defining a duty cycle. The processor is programmed to determine the temperature at the electrode/tissue interface based on the temperature signals, compare the temperature to a target temperature and to adjust the power to the electrode accordingly.

Abstract: A catheter carries a plurality of electrodes, each with multiple thermal sensors attached and is used to position the electrodes proximal biological tissue. A processor responsive to each of the thermal sensors determines the temperature at the thermal-sensor/electrode junction. A display provides a graphic representation of the temperatures of the thermal-sensor/electrode junctions. An exemplary representation is a bar graph having the temperature of one thermal sensor at one end and the temperature of another thermal sensor at the other end. The length of the bar graph combined with the position of the bar graph relative to a temperature range region provides an indication of the position of the thermal-sensor/electrode junctions relative to the biological tissue. The processor also monitors the spread between the sensor temperatures and compares it to a threshold value. Base on the result of the comparison, the processor controls the power applied to the electrode.

Abstract: A pulse having a high-frequency cyclic waveform with a plurality of cycle groups is applied across a defribrillating heart. The waveform has, during the first cycle group, an initial peak-to-peak voltage and, during each subsequent cycle group, a peak-to-peak voltage that may be substantially equal to or less than that of the previous cycle group. In one application, the subsequent cycle groups have progressively decreasing peak-to-peak voltages and the profile of the cyclic waveform resembles a discharge curve of a capacitor. In another the subsequent cycle groups have substantially equal peak-to-peak voltages and the cyclic waveform has a substantially constant peak-to-peak amplitude throughout the duration of the pulse. The waveform of the pulse has substantially no dc component. The total energy delivered to the heart is controlled by adjusting the initial and subsequent peak-to-peak voltages and by varying the time duration of the pulse.

Abstract: A method of assessing the adequacy of contact between an ablation electrode and biological tissue within a biological organ having biological fluid therein includes the steps of positioning the ablation electrode proximal the biological tissue; positioning a reference electrode a distance from the ablation electrode; measuring the impedance between the ablation electrode and the reference electrode at a first frequency and measuring the impedance between the ablation electrode and the reference electrode at a second frequency. The percentage difference between the first-frequency impedance and the second-frequency impedance provides an indication of the state of electrode/tissue contact. In general, a percentage difference of at least approximately 10% serves as an indication of substantially complete electrode/tissue contact. A percentage difference in the approximate range between 5% and 10% serves as an indication of partial electrode/tissue contact.

Abstract: An apparatus for delivering energy to a biological site includes an electrode device having a plurality of electrodes, the electrode device positioned proximal the biological site. A power control system supplies power having a controllable phase angle to each of the electrodes. A backplate is also positioned proximal the biological site so that the biological site is interposed between the electrode device and the backplate. The backplate is maintained at the reference voltage level in relation to the power. The power control system controls the phase angle of the power so that the current flow between the electrodes and between the electrodes and the backplate results in the continuity and depth of lesions desired. In a preferred embodiment, the electrodes are arranged in a substantially linear array.

Abstract: An apparatus for delivering energy to a biological site includes an electrode device having a plurality of electrodes, the electrode device positioned proximal the biological site. A power control system supplies power having a controllable phase angle to each of the electrodes. A backplate is also positioned proximal the biological site so that the biological site is interposed between the electrode device and the backplate. The backplate is maintained at the reference voltage level in relation to the power. The power control system controls the phase angle of the power so that the current flow between the electrodes and between the electrodes and the backplate results in the continuity and depth of lesions desired. In a preferred embodiment, the electrodes are arranged in a substantially linear array.

Abstract: An apparatus for delivering energy to a biological site includes a catheter having a plurality of electrodes positioned proximal the biological site. A power control system supplies power to each electrode. Where an electrode or group of electrodes is turned off, the power control system provides a high impedance to the turned off electrodes so that substantially no current flows to those electrodes from other electrodes that may remain on. This permits the electrodes turned off to cool. The power control system may permit control over the phase and duty cycle of the power applied to the electrodes and may permit individual control over the power provided to each electrode. A backplate is also positioned proximal the biological site so that the biological site is interposed between the electrodes and the backplate.

Abstract: An apparatus for delivering energy to a biological site includes an electrode device having a plurality of electrodes, the electrode device positioned proximal the biological site. A power control system supplies power having a controllable phase angle to each of the electrodes. A backplate is also positioned proximal the biological site so that the biological site is interposed between the electrode device and the backplate. The backplate is maintained at the reference voltage level in relation to the power. The power control system controls the phase angle of the power so that the current flow between the electrodes and between the electrodes and the backplate results in the continuity and depth of lesions desired. In a preferred embodiment, the electrodes are arranged in a substantially linear array.

Abstract: An apparatus for delivering energy to a biological site includes a catheter having a plurality of electrodes, the electrodes positioned proximal the biological site. A power control system supplies power signals, each having a controllable phase angle, to each of the electrodes such that the phase between electrodes alternates. A backplate is also positioned proximal the biological site so that the biological site is interposed between the electrode device and the backplate. The backplate is maintained at one voltage level in relation to the power. The power control system controls the phase angle of the power so that the current flow between the electrodes and between the electrodes and the backplate results in the continuity and depth of lesions desired. In a preferred embodiment, the electrodes are arranged in a substantially linear array.

Abstract: An apparatus for delivering energy to a biological site includes a catheter having a plurality of electrodes arranged in a linear array, the electrodes positioned proximal the biological site. A power control system supplies power, each having a controllable duty cycle and phase angle, to each of the electrodes. A backplate is also positioned proximal the biological site so that the biological site is interposed between the electrode device and the backplate. The backplate is maintained at the reference voltage level in relation to the power. The power control system controls the phase angle of each power signal so that current flows between the electrodes and between the electrodes and the backplate results. Temperature sensors are located at the electrodes and each shares a common lead with the power circuitry. The temperature sensor signal is received by the power control system during the off-period of the duty cycle of the particular electrode.

Abstract: The non-joined thermocouple electrode configuration, for use in an RF ablation catheter for ablating biological tissue such as cardiac tissue, allows temperature to be monitored at two locations of a band electrode while only using a single pair of thermocouple wires. The thermocouple wires are connected to the electrode at separate locations. They preferably are formed of metallic materials having Seebeck coefficients that are substantially equal in magnitude but opposite in sign relative to the electrode material connecting the two. In the case of a band electrode, the two thermocouple wires are preferably spaced apart on the band electrode so that the first junction contacts the tissue having a first temperature and the second junction contacts circulating blood having a second temperature.

Abstract: A power control system and method controls a power generator to vary the duty cycle of a power output provided to a delivery instrument for delivering that power to a site in a patient for ablation. The peak power can be raised and the duty cycle lowered to result in deeper lesions. However, the effective power is controlled so that it does not exceed a predetermined level. A power output having a higher peak power for producing deeper lesions can be obtained by using a lower duty cycle having a longer "off" period in order to deliver more power to the ablation site without overheating the delivery instrument. The maximum peak power that may be selected is determined in accordance with the structural limitations of the delivery instrument. The temperature of the delivery instrument is monitored, and the duty cycle is lowered when the temperature exceeds a predetermined maximum limit. After the instrument has cooled sufficiently, the duty cycle is then increased to its previous level.

Abstract: A method and apparatus for measuring resistance of a blood sample in order to determine the hematocrit of that blood sample. The present invention makes a direct ratiometric measurement. That is, the alternating current that flows through the sample is directly measured by applying that alternating current to an integrator which converts the current to a D.C. voltage which is directly proportional to the applied current.

Abstract: An energy delivery system and method controls the frequency of the power driving an ultrasonic device to achieve more efficient power delivery. During operation of the ultrasonic device to deliver power to a patient site, the system and method automatically sweeps the drive power through a frequency range, locates the series and parallel resonance frequencies, calculates the average of those frequencies and locks the power generator at that average frequency to drive the crystal. This frequency sweep procedure occurs automatically when the ultrasonic crystal is located at the patient site and the power generator operator presses the power-on switch to apply power. The method of tuning the power generator thus occurs when the crystal is at the site temperature and is transparent to the operator. The application of an external bio-layer to the crystal increases its bandwidth and its robustness.