as used herein , the term “ pulse ” refers to a single occurrence of an electrical signal that has a defined shaped and period . as used herein , the term “ waveform ” refers to a repeating electrical signal that may include one or more pulses . the pulses that make up the waveform may be the same or may differ in any one of shape , polarity , duration and amplitude . for example , a biphasic waveform may include an anodal pulse and a cathodal pulse . the anodal and cathodal components may differ only in polarity or may be differ in shape , polarity , duration and amplitude . pulses making up a waveform may differ in shape , polarity , duration , and amplitude but be equivalent in power . as used herein , the term “ sub - threshold waveform ” refers to a waveform that does not result in stimulating the heart to beat . a waveform may be sub - threshold because the amplitude of the waveform is below an amplitude threshold value necessary to stimulate a heartbeat . a waveform may be sub - threshold because the duration of the waveform is below a duration threshold value necessary to stimulate a heartbeat . a waveform may be sub - threshold because the power of the waveform is below a power threshold value necessary to stimulate a heartbeat . as used herein , the term “ pacing waveform ” refers to a waveform that stimulates a heartbeat , results in depolarization and is by definition equal to or greater than a threshold necessary to simulate a heartbeat . fig1 shows a representative tracing 10 of electrical activity in a typical heartbeat . a p wave 11 represents the wave of depolarization that spreads from the sa node throughout the atria . a period of time from the onset of the p wave to the beginning of a qrs complex is known as the p - r interval 12 . the p - r interval 12 represents the time between the onset of atrial depolarization and the onset of ventricular depolarization ( typically lasting 20 - 200 ms ). if the p - r interval is & gt ; 200 ms , there is an av conduction block , which is also known as a first - degree heart block if the impulse is still able to be conducted into the ventricles . a qrs complex 13 represents the period of ventricular depolarization , which normally occurs very rapidly ( e . g ., typically lasting 80 - 120 ms ). if the qrs complex is prolonged , conduction is impaired within the ventricles . the isoelectric period ( st segment 14 ) following the qrs complex 13 is the period of time ( typically lasting 80 - 120 ms ) at which the entire ventricle is depolarized and roughly corresponds to the plateau phase of the ventricular action potential . the st segment 14 is important in the diagnosis of ventricular ischemia or hypoxia because under those conditions , the st segment 14 can become either depressed or elevated . fig2 is a schematic representation illustrating a multi - phase cardiac stimulus generator 120 implanted in a patient according to an embodiment . in an embodiment , one or more sensors sense rhythm and contractions of the patient &# 39 ; s heart 105 using at least one of atrial sensing and ventricular sensing , such as at least one of atrial sensor 110 and ventricular sensor 112 . the atrial sensor 110 and / or ventricular sensor 112 provide sensor data to a rules engine 122 . in an embodiment , the rules engine includes a processor 126 and a memory 124 for storing rules and receiving sensor data . the rules engine 122 may poll the one or more of the atrial sensor 110 and the ventricular sensor 112 to obtain sensor data and to apply the rules to the sensor data in order to determine whether to deliver electrical waveforms to one or more electrodes , and , if electrical waveforms are to be delivered , which of the one or more electrodes is to receive the electrical waveforms . in an embodiment , the one or more electrodes may be an atrial electrode 114 and a ventricular electrode 116 , and may provide electrical waveforms to at least one of an atrial chamber and a ventricular chamber of the heart 105 . the multi - phase cardiac stimulus generator 120 may generate an anodal waveform , a cathodal waveform , and a biphasic waveform above or below threshold depending on the sensor data and the rules applied by the rules engine 122 . in an embodiment , the memory 124 of the rules engine 122 of the multi - phase cardiac stimulus generator 120 is configured to store one or more anodal waveforms , cathodal waveforms , and biphasic waveforms . a waveform or a combination of waveforms may be selected from the memory 124 by the processor 126 based on sensor data and based on rules also stored in memory 124 . in an embodiment , the memory 124 also stored information about the patient 100 . the processor 126 may further select a waveform or a combination of waveforms from the stored waveforms based on the sensor data and data about the user . in an embodiment , the stored waveforms comprise waveform data that are used by the multi - phase cardiac stimulus generator 120 to produce waveforms for applying to the heart 105 . in an embodiment , different pacing waveforms are generated by the multi - phase cardiac stimulus generator 120 to differentially increase or decrease conduction , vigor of conduction , and repolarization in various directions , amounts , and combinations . for example , a patient with idiopathic hypertrophic subaortic stenosis ( ihss ) may experience vigorous contraction of the iv septum , which leads to lv outflow tract obstruction . this condition can be relieved by generating and applying a pacing the septum with a monophasic cathodal waveform . a patient with congestive heart failure ( chf ) can be improved by speeding conduction and resyschronizing the heart muscle by reducing the qrs width by generating and applying biphasic pacing waveforms . in another embodiment , various non - stimulatory waveforms of different polarities , combinations , and timings may be selectively generated by the multi - phase cardiac stimulus generator 120 to affect ion channels involved in repolarization specifically and selectively . for example , a waveform may be generated by the multi - phase cardiac stimulus generator 120 to normalize abnormalities resulting from genetic disorders and various medications . in an embodiment , the total duration of these waveforms can also be optimized to promote stimulation of nervous tissue , myocardium , or skeletal muscle . in an embodiment , the one or more atrial sensor 110 and / or ventricular sensor 112 may include sensors that measure various measures of heart activity and health . by way of illustration and not by way of limitation , sensors may be used to measure heart size , asynchronicity of contractions , back pressures in various parts of the heart , intrinsic qrs width , resting membrane potential ( rmp ), and after potentials of the action potential . by way of illustration and not by way of limitation , measurements may be taken using intra - cellular plunge electrodes , monophasic action potential ( map ) catheters , and optical probes . the sensor data may be used to diagnose various abnormal conditions and / or to generate waveforms to treat one or more conditions . in an alternative embodiment , only a limited number of waveforms are stored in the memory 124 of the rules engine 122 of the multi - phase cardiac stimulus generator 120 . the stored waveforms may be selected based on the condition of the patient and the anticipated abnormal states that the patient may encounter . the stored waveforms may be differentiated based on a strength and a duration of an anodal portion of the biphasic waveform . the stored waveforms may also be differentiated based on a strength and a duration of a cathodal portion of the biphasic waveform . for example , a shorter waveform may be used to enhance conduction without stimulating the heart . this will allow intrinsic conduction to be normalized . in an embodiment , the sensor data in conjunction with the user data may follow a non - stimulatory short waveform with a stimulatory biphasic or cathodal pacing waveform . alternatively , a longer waveform may be used to enhance contractility . in an embodiment , the selection of a biphasic waveform and / or a cathodal waveform may be based on sensor data . for example , sensor data may be acquired from atrial sensor 110 , ventricular sensor 112 , or other sensors . for example , the sensor data may be acquired from the atrial sensor 110 and a septum sensor ( not illustrated ) to evaluate the condition of the patient . an appropriate waveform may be selected the processor 126 . a patient may have different heart conditions simultaneously . the sensor data may be used to select an appropriate waveform from memory 124 and to provide the appropriate waveform data to the multi - phase cardiac stimulus generator 120 . the selected waveform is then applied to the heart , and the heart rhythm is sensed . the new sensing data may be used to again apply the waveform to the heart , to modify the strength of the applied waveform and to apply the modified waveform to the heart , to apply a different waveform to the heart , or to cease stimulating the heart . a system and method for stimulating the heart via storage of multi - waveforms in a cardiac stimulation device t have been disclosed . it will also be understood that the invention may be embodied in other specific forms without departing from the scope of the invention disclosed and that the examples and embodiments described herein are in all respects illustrative and not restrictive . those skilled in the art of the present invention will recognize that other embodiments using the concepts described herein are also possible . further , any reference to claim elements in the singular , for example , using the articles “ a ,” “ an ,” or “ the ” is not to be construed as limiting the element to the singular .
a rules engine acquires sensor data from sensors applied to the heart and determines whether an electrical waveform should be applied to the heart and , if so , the type of electrical waveform . a multi - phase cardiac stimulus generator generates waveforms in response to the rules engine from waveform data stored in a memory . the electrical waveform is applied to one or more electrodes implanted in or on the heart .