Patent Application
20080091239
The pacing pulse generator 4 is operated by pacing logic 7.
The electrode 5 is also connected to a sense amplifier 8, which receives and detects signals via the lead 5 and the electrode 6 representing electrical activity of the heart 2. The output of the sense amplifier 8 is connected to a control unit 9, that provides control signals and setting to the pacing logic 7 for operating the pacing pulse generator 4.
In accordance with the invention, the microphone 1 communicates with a microphone signal evaluator 11 in the housing 3 via a lead 10. The placement site of the microphone 1 in the embodiment of
The microphone signal evaluator 11 evaluates an electrical signal generated by the microphone 1 that results from the simultaneous detection of heart and lung sounds at the placement site of the microphone 1. The microphone signal evaluator 11 makes use of the fact that blood is non-neutonian fluid that contains platelets in the form of red blood cells. Such a fluid is prone to create vortices as it flows through the circulatory system. A vortex is always accompanied by one or more pressure fluctuations. These fluctuations are picked up by the microphone 1. The frequency of the vortices is directly correlated to the flow velocity, and allows the microphone signal evaluator 11 to analyze the microphone signal to measure blood flow. As long as the simultaneously detected heart and lung sounds always originate from the same location, i.e., the placement site of the microphone 1, changes in blood flow can be determined.
It can be theorized that insufficient lubrication in the pericardial sac will cause the generation of friction-related sounds. These sounds can be expected to include short, high-frequency snaps from slipping movements. These sounds can also be detected by the microphone 1. The unique characteristic of this sound simplifies any filtering that may be necessary to extract such a sound from the overall microphone signal.
As noted above, the platelets (red blood cells) play an essential role in the generation of vortices. This means that the more red blood cells, the more vortices, and thus the stronger the microphone signal. Changes in signal strength are thus an indication of changes in hematocrit level. Many techniques for analyzing sounds (not necessarily devised for analyzing heart and lung sounds) are known, that involve time-domain analysis or frequency-domain analysis, or combinations thereof. Different heart rhythms create characteristic “footprints” depending on the origin and placement of the microphone 1. Based on these characteristics, discrimination among super-ventricular tachycardia (SVT) ventricular tachycardia (VT) and ventricular fibrillation (VF) can be made. Detection of beat-to-beat alternans during ischemia is another type of analysis that can be made.
It is also possible to detect atrial fibrillation (AF) by analyzing the simultaneously detected heart and lung sounds in the microphone signal evaluator 11. AF is a common condition, and although it is generally not life threatening by itself, it causes an increased risk of emboli, as well as discomfort, and weakens the ability of the heart to supply the body with oxygenated blood.
Moreover, AF may lead to several more serious conditions, and also is a predictor for several diseases. VF, unlike AF, is life threatening, and must be treated immediately, when detected. The sound of a fibrillating heart differs significantly from that of sinus rhythm, regardless of the heart rate, and thus offers a very useful complement or alternative to conventional electrical detection of fibrillation.
Another type of condition that can be detected by the analysis in the microphone signal evaluator 11 is the occurrence of post-ventricular contractions (PVC) and supra-ventricular contractions (SVC). When a PVC occurs, the filling is not complete, resulting in a quieter sounding valve than in the case of a normal beat. The following beat will then be more powerful than usual, and thus produce a louder sound, as there is an abnormal filling of the ventricle.
Moreover, irregular contractions of the heart that are not triggered by the sinus node or the normal conduction pathways of the heart often cause an extraordinary sound that differs from normal heartbeats. An example are so-called “cannon waves” that occur when the atrium contracts while the mitral valve is still closed, causing a backward rush of blood.
The control unit 9 can make use exclusively of the analysis or evaluation result from the microphone signal evaluator 11, but preferably also makes use of an analysis result of the electrical signal from the sense amplifier 8. The “final decision” for setting a cardiac-assist therapy that is made by the control unit 9 can be based on both of these analysis results, such as by a weighted combination. Alternatively, one analysis result can be used as a confirmation of the other analysis result.
The control unit appropriately controls the pacing logic 7 if and when the cardiac-assist therapy to be administered is a brady pacing regimen and/or ATP.
If the control unit 9 determines that a condition of VF exists, the control unit 9 then operates a cardioversion/defibrillation pulse generator 12 connected thereto that generates one or more defibrillation pulses, that are delivered to the heart 2 via a lead 13 connected to an electrode coil 14. As is known, the coil 14 is typically placed in the superior vena cava or the great vein.
It will be understood by those of ordinary skill in the field of designing cardiac assist devices that one or more suitable return paths must be provided for the electrode 6 and the electrode coil 14. Any suitable return electrode can be used, and therefore the return electrode or electrodes are not shown in
Moreover, those of ordinary skill will also be aware that the housing 3 contains a battery (not shown) for supplying power to the components contained in the housing 3.
The control unit 9 is in communication with a telemetry unit 15 that has an antenna 16 allowing wireless communication with an extracorporeal programmer 17 that has an antenna 18. The control unit 9 can include, or be in communication with, a memory (not shown) in the implantable housing 3, so that the microphone signal, or the analysis results obtained therefrom, can be stored together with other data that are typically stored during the operation of a conventional cardiac-assist device. The stored data can be downloaded via the telemetry unit 15 at appropriate times to the extracorporeal programmer 17, so that the data can be evaluated in further detail, as needed, by a cardiologist. The data can be visually displayed at the extracorporeal programmer, and/or a printout of the data can be undertaken.
As described in the article “Presystolic Augmentation of Diastolic Heart Sounds in Atrial Fibrillation,” Bonner, Jr. et al., Am. J. Cardiol., Vol. 37, No. 3 (Mar. 4, 1976), pages 427-431, during atrial fibrillation the diastolic murmur of mitral stenosis can appear augmented during systole before the mitral valve closure sound. It is also known that during VF, no real contractions of the heart are occurring, and thus it is feasible to interpret a lack of “normal” heart sound, as usually occurs during sinus rhythm, as evidence of VF.
An example of analysis associated with AF that can be performed by the device of
If no occurrence of AF is determined to exist, sensing continues as before, as indicated by the block 22. If AF is determined to be present, and is serious enough to require cardiac-assist therapy, one or more cardioversion pulses can be administered, as indicated by the block 23.
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 hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
