1. Field of the Invention
The present invention relates to a system for detecting electric cardiac events in chambers of a heart of the type having leads with electrodes adapted for implantation in at least two different chambers of the heart for sensing electric signals therein, and a difference former provided to supply a difference signal, formed of the signals sensed by the electrodes, to an event detector, arranged to distinguish, from the difference signal, between events originating from one of the chambers from events originating from the other one of the chambers. The invention also relates to a corresponding method and a heart stimulator embodying such a system.
2. Description of the Prior Art
Multi-chamber sensing system for use in e.g. multi-chamber pacing systems, need to sense electrical cardiac events, like P and R-waves, at several positions inside or outside of the heart muscle. Leads provided with one or more electrodes are used for this purpose.
Bipolar sensing of both atrial and ventricular events is thus described in U.S. Pat. No. 5,800,468.
Differential sensing between unipolar electrode leads located in the right atrium and the right ventricle is disclosed in U.S. Pat. No. 5,871,507.
In United States Patent Application Publication No. 2001/0049543 biventricular stimulation and capture monitoring are described. For capture detection cross-chamber sensing electrode configurations are used. Multipolar leads are used and different electrodes are used for stimulation and sensing. Sensing between a right ventricular ring electrode and a left atrial ring electrode is described as well as between right and left ventricular ring electrodes.
To be able to position electrode leads in the coronary veins for stimulation and sensing on the left ventricle and atrium of as many patients as possible with varying anatomy, it is important that the leads are as thin and flexible as possible. Leads with at least an unipolar distal end portion are easier to make thin and flexible and are therefore normally easier to implant in the coronary veins. However, when using an unipolar electrode for sensing with the stimulator or sensing apparatus case as indifferent electrode, the signal-to-noise ratio often becomes unacceptable low.
An object of the present invention is to solve this problem and make detection of capture and loss of capture possible in all the chambers of the heart, also of the left atrium and left ventricle without using the above-mentioned conventional unipolar sensing which often results in a too low signal-to-noise ratio as mentioned.
The above object is achieved in accordance with the present invention by a system for detecting electrical cardiac events in chambers of a heart, having multiple leads each provided with at least one electrode, the lead being respectively configured for implementation in at least two different chambers of the heart for sensing electrical signals in those chambers, and a difference former connected to the leads that emits a difference signal formed by the respective signals sensed by the electrodes of the respective leads, and an event detector, supplied with the different signals, that distinguishes between electrical events originating in one of the chambers and electrical events originating in the other of the chambers, wherein at least one of the leads is adapted for implantation in a coronary vein of the art for sensing a left atrial signal or a left ventricular signal.
The above object also is achieved by a cardiac stimulator embodying such a detection system, as well as by a method that includes sensing a left atrial signal or a left ventricular signal using a lead configured for implantation in a coronary vein of a heart.
Thus, according to the present invention detection of electric cardiac events is possible in any one of the four chambers of the heart while avoiding the disadvantage of the above discussed, previously used technique for unipolar sensing by performing the sensing between electrodes located within or on the heart.
According to an advantageous embodiment of the system according to the invention the leads adapted for implantation in a coronary vein on the left side of the heart are unipolar. The use of unipolar left side leads involves several important advantages. Unipolar leads are thinner than bipolar leads, they are softer and more flexible at the distal end portion, have a simpler mechanical construction and a better longevity. An unipolar lead can be more easily bent distally using a pre-bent or steerable stylet which is important for making passage of sharp bends in coronary vessels possible. It is also easier to slide a unipolar lead over a sharply bent guidewire inside a coronary vein and to retract the guidewire after positioning the lead tip in a proper position. Bipolar leads, on the other hand, are often too thick for implantation in all the coronary veins which can be candidates for e.g. left ventricular stimulation and sensing. It can for instance be impossible to pass a sharp bend because the distal end of the bipolar lead is too stiff. The advantages of bipolar leads are that they normally give a higher signal-to-noise ratio, and bipolar stimulation reduces the risk of muscular stimulation at the stimulator case. Bipolar sensing can, however, sometimes be difficult when an action potential is passing both electrodes simultaneously and the signals are similar. In such a case unipolar sensing is preferred. Phrenicus stimulation also often requires attention at left ventricular pacing, since bipolar pacing on the left ventricle increases the risk of phrenicus stimulation because both the tip and the ring are involved. With this embodiment of the invention the risk of phrenicus stimulation is reduced compared to normal bipolar or unipolar stimulation which also can result in pectoral muscle stimulation when higher stimulation amplitudes are needed. In summary, with the present embodiment the physician will be more free to find an optimal location of the implanted lead on the left side of the heart, which can result in a higher phrenicus stimulation threshold, better hemodynamics and low stimulation threshold, while not losing the good properties of using bipolar leads.
When stimulating between tip electrodes located in the left and right ventricles it is difficult to detect evoked response between the tips, because the difference signal can be small or totally disappear in case of capture on both the ventricles. In this case a detection can be erroneously interpreted as loss of capture in both ventricles instead of capture in both ventricles. According to other advantageous embodiments of the system according to the invention, the event detector is therefore arranged to distinguish, after bi-ventricular stimulation, between capture and non-capture from the difference signal, formed of signals sensed by an electrode positioned in the left ventricle and by a differently positioned electrode on the right side of the heart, the differently positioned electrode on the right side of the heart preferably being a ring or coil electrode. In this way there will be a time lag between evoked response signals sensed in the right and left side of the heart depending on the distance between the ventricular tip electrode and the differently positioned electrode on the right side of the heart and on the propagation velocity of the action potential in the myocardium, when pacing takes place simultaneously on both sides of the heart and capture of both ventricles is obtained.
According to still another advantageous embodiment of the system according to the invention the electrodes are adapted for implantation in a coronary vein on the left atrium, and in a coronary vein on the left ventricle or in the right ventricle respectively. Sensing between a tip electrode in the left atrium and a tip electrode in the left ventricle can be an attractive alternative. It is possible to distinguish between a P-wave and a R-wave from the direction of the rapid voltage change when the action potential passes the electrodes. By using an electrode in one of the ventricles as indifferent electrode when sensing P-waves in the left atrium interference of P-waves in the right atrium is avoided.
The curve at the bottom of
The second curve from below in
The second curve from the top of
The curve at the top of
From
One way of distinguishing between capture of both ventricles and loss of capture for both ventricles is to perform a separate R-wave detection. In U.S. Pat. No. 6,148,234 an R-wave detector is described which is enabled from the delivery of a stimulation pulse to the end of the heart refractory period, a period of normally about 300 msec. If R-waves are detected in this period there has been loss of capture in one of the ventricles.
Another way of distinguishing capture of both ventricles from loss of capture for both ventricles is to study separately the signals from RV and LV respectively in case of detection of no difference signal.
Still other possibilities of distinguishing capture of both ventricles from loss of capture for both ventricles will be described below.
Sensing between tip electrodes in RV and LV gives almost a bipolar suppression of noise signals. In
By high pass filtering or differentiating the signal in
As described above a suitable high pass filter can be used for making it easier to distinguish between different cardiac events. High pass filtering will enhance the fast derivatives of the IEGM, cf. the discussion above of
Another technique for distinguishing between cardiac events originating from one of said chambers from events originating from the other one comprises morphology analysis of the difference signal. When the action potential passes the electrode the potential is first raised, thereafter a fast negative slope occurs followed by a return to the baseline. Depending on which (positive or negative) inputs of the difference forming means 4 the electrodes A and B are connected to, see
In this connection it could be noted that bi-ventricular pacing between the tip electrodes in RV and LV can create capture in both ventricles simultaneously by one single pacing pulse. Normally the anodic stimulation threshold is higher than the cathodic one. Therefore it is possible to change pacing polarity so that the electrode with the higher stimulation threshold is stimulated cathodically (negatively) and the electrode with the lower stimulation threshold—normally the tip electrode in RV—is stimulated anodically (positively). The transventricular (right ventricular tip electrode to left ventricular tip electrode) stimulation threshold will then be lower. Transventricular pacing will also be associated with a low risk of creating phrenicus nerve stimulation, because the pacing current flows through the heart and not to the pacemaker case or along the lead.
As explained above it is preferred to use unipolar electrodes on the left side of the heart. It is well known to use unipolar as well as bipolar electrodes in the right side of the heart. In this connection it could be an advantage to use bipolar electrodes in right atrium and right ventricle.
Above sensing of evoked response between tip electrodes in RV and LV respectively when pacing between the two tip electrodes has been described. As explained above, when detecting evoked response, ER, between ventricular electrode tips in this way the difference signal can be very small or totally disappear when having capture on both ventricles or loss of capture on both ventricles, see
In the left part of
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted heron all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/SE2006/000143 | 1/31/2006 | WO | 00 | 11/5/2008 |