Biventricular cardiac stimulator

An implantable cardiac stimulator (10), comprising

• at least one right ventricular sensing unit (58) which has a first input that is configured to be connected to a right ventricular electrode line (16) and is configured to analyze a first electric input signal applied to the first input, such that the at least one right ventricular sensing unit detects at least one first signal feature typical of a contraction of a right ventricle and generates a corresponding first output signal;
• at least one right ventricular stimulation unit (56) which has a first output that is configured to be connected to the right ventricular electrode line (16) and is configured to generate a right ventricular stimulation pulse in response to a first control signal and deliver the right ventricular stimulation pulse via the first output;
• at least one left ventricular sensing unit (66) which has a second input that is configured to be connected to a left ventricular electrode line (30) and and is configured to analyze a second electric input signal applied to the second input, such that the at least one left ventricular sensing unit detects at least one second signal feature typical of a contraction of a left ventricle and generates a corresponding second output signal;
• at least one left ventricular stimulation unit (64), which has second output that is configured to be connected to the left ventricular electrode line (30) and is configured to generate a left ventricular stimulation pulse in response to a second control signal and deliver the left ventricular stimulation pulse via the second output;
• a stimulation control unit (54) which is connected to the at least one right ventricular sensing unit (58), the at least one left ventricular sensing unit (66), the at least one right ventricular stimulation unit (56) and the at least one left ventricular stimulation unit (64) and is configured to process the first and second output signals of the at least one right ventricular sensing unit (58) and at least one left ventricular sensing unit (66) and to generate the first and second control signals for the at least one right ventricular stimulation unit (56) and the at least one left ventricular stimulation unit (64) to generate near field stimulation pulses sufficient to excite myocardium proximal to a distal end of said right ventricular electrode line and said left ventricular electrode line respectively;
• and,
• wherein the stimulation control unit (54) is configured to switch a mode of operation between at least one right ventricular stimulation mode configured to generate near field stimulation pulses
• in which no control signals to trigger left ventricular pulses are output to the at least one left ventricular stimulation unit, and
• a biventricular stimulation mode alternately, configured to generate near field stimulation pulses;
• wherein the stimulation control unit is additionally configured to switch the mode of operation as a function of a signal that indicates a duration of a prevailing QRS signal interval of a certain signal or any of the first and second electric input signals, such that the stimulation control unit switches to
• the biventricular stimulation mode configured to generate near field stimulation pulses only when a comparison of the signal that indicates the duration of the prevailing QRS signal interval with a first comparison value reveals that the duration of the prevailing QRS signal interval is longer than a first reference value represented by the first comparison value for a predefined plurality number of cardiac cycles in a row,
• and switches to
• the at least one right ventricular stimulation mode configured to generate near field stimulation pulses only when the comparison of the signal that indicates the duration of the prevailing QRS signal interval with a second comparison value reveals that the duration of the prevailing QRS signal interval is shorter than a second reference value represented by the second comparison value for a predefined plurality number of cardiac cycles in a row;
• a timer coupled with said stimulation control unit;
• wherein the stimulation control unit comprises an intrinsic VV interval conduction time measuring unit, an intrinsic VV interval comparison unit and a stimulation mode switch;
• such that the intrinsic VV interval conduction time measuring unit is configured to cooperate with the timer to
• determine an intrinsic VV interval conduction time in a biventricular CRT stimulation mode, wherein said intrinsic VV interval reflects an interval of time between the contraction of the right ventricle detected by the at least one right ventricular sensing unit (58) and a contraction of the left ventricle to be causally assigned to a right ventricular contraction detected by the at least one left ventricular sensing unit (66), and
• determine a left ventricular stimulation point in time that occurs after the end of the respective intrinsic VV interval thereby determined.