Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-04-27
2002-08-27
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06442427
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cardial pacing systems, and, in particular, to cardial pacing systems providing for the immediate contractual stimulation of an atrium of a mammalian heart upon the detection of a premature atrial contraction in a second atrium.
BACKGROUND OF THE INVENTION
The cardiovascular system provides oxygenated blood to various structures of the body. In a normally functioning heart, the body's demand for oxygenated blood varies, and the heart responds by increasing or decreasing its rate and force of contraction to meet the demand. An electrical signal generated by the sinus node in the upper right atrial wall near the base of the heart is transmitted through the two upper heart chambers, i.e., the right and left atria, which causes them to synchronously contract. The contraction of the two upper heart chambers forces blood, pooled within the chambers, through open heart valves and into the right and left ventricles, the two lower heart chambers. The atrial electrical depolarization wave arrives at the atrio-ventricular (AV) node, superior to the ventricles, and triggers the conduction of a ventricular depolarization wave down the bundle of His in the septum between the right and left ventricles to the apex of the heart. The two ventricles contract after a brief AV delay time following the sinus node depolarization as the depolarization wave then advances superiorly, posteriorly, and anteriorly throughout the outer ventricular wall of the heart. The two lower heart chambers contract and force the blood through the vascular system of the body. The contraction of the right and left ventricles then proceeds in an organized fashion which optimizes the emptying of the ventricular chambers. The synchronous electrical depolarization of the atrial and ventricular chambers can be electrically sensed and displayed, and the electrical waveform is characterized by accepted convention as the “PQRST” complex. The PQRST complex includes the P-wave, which corresponds to the atrial depolarization wave; the R-wave, corresponding to the ventricular depolarization wave; and the T-wave, which represents the re-polarization of the cardiac cells.
Various disease mechanisms may cause conduction disturbances which interfere with the natural conduction system of the heart and affect the heart's ability to provide adequate cardiac output to the body. In certain disease mechanisms, the sinus node may fail to depolarize and commence the P-wave as rapidly as required to satisfy the demand for oxygenated blood, or the atria themselves may spontaneously depolarize at rates that are well in excess of the ability of the ventricles to respond. In such situations, the ventricles may compensate by depolarizing spontaneously from ectopic depolarization sites. In other cases in which the sinus node operates correctly, 1:1 atrial and ventricular depolarization synchrony is lost because the AV node may fail to respond to the P-waves or a defect in the bundle of His interferes with the conduction of the ventricular depolarization. In these cases, the ventricles may contract at a rate inadequate for providing sufficient cardiac output.
When either the atria or ventricles contract too slowly, the patient may be a candidate for implantation of a cardiac pacemaker for restoring the heart rate by applying pacing pulses to the heart chamber that is malfunctioning at a pacing rate that restores adequate cardiac output. Modern implantable cardiac pacemakers comprise an implantable pulse generator (IPG) and a lead or leads extending from the IPG to pace/sense electrode or electrodes located with respect to the heart chamber to deliver the pacing pulses and/or sense the P-wave or R-wave. Typically, the leads are transvenously introduced into the particular heart chamber via the superior vena cava and right atrium, and the pace/sense electrodes are maintained in contact with the heart tissue by a fixation mechanism at the distal end of the lead. However, leads may be placed subcutaneously between the IPG and the exterior or the heart, and the pace/sense electrodes attached to the epicardium at the desired sites. Moreover, enocardial coronary sinus leads are introduced through the right atrium into the coronary sinus and the great vein to locate pace/sense electrodes in proximity to the left atrium or the left ventricle.
A single chamber, demand pacemaker may be implanted into the patient to supply pacing pulses to a single upper or lower heart chamber, typically the right atrium or right ventricle, in response to bradycardia of the same chamber. In an atrial demand pacemaker operating in an AAI pacing mode, an atrial pacing pulse is delivered to the atrial pace/sense electrodes by the IPG if a P-wave is not sensed by an atrial sense amplifier coupled to the artial pace/sense electrodes within an atrial escape interval (A-A interval) timed by an atrial escape interval timer. In a ventricular demand pacemaker operating in a VVI pacing mode, a ventricular pacing pulse to the ventricular pace/sense electrodes if an R-wave is not sensed by a ventricular sense amplifier coupled to the ventricular pace/sense electrodes within a ventricular escape interval (V-V interval) timed by a ventricular escape interval timer.
Additionally, a dual chamber, demand pacemaker may be implanted into the patient to supply pacing pulses, when required, to one upper heart chamber and to one lower heart chamber, typically the right atrium and the right ventricle. In a dual chamber, demand pacemaker operating in a DDD pacing mode, both the AAI and VVI modes are followed, under the above defined conditions. A ventricular pacing pulse is delivered to the ventricular pace/sense electrodes if an R-wave is not sensed by the ventricular sense amplifier coupled thereto within an AV time interval timed from the sensing of a P-wave by the atrial sense amplifier.
Over the years, it has been proposed that various conduction disturbances involving both the bradycardia and the tachycardia of the heart chamber could benefit from stimulation applied at multiple electrode sites positioned in or about it in synchrony with a depolarization which has been sensed at least one of the electrodes sites. In addition, it has been proposed to employ pacing to compensate for conduction defects and in congestive heart failure where depolarizations that naturally occur in one upper or lower chamber are not conducted quickly enough to the other upper or lower heart chamber. In such cases, the right and left heart chambers do not contract in optimum synchrony with each other, and the cardiac output suffers due to the timing imbalance. In other cases, spontaneous depolarizations of the left atrium or left ventricle occur at ectopic foci in these left heart chambers, and the natural activation sequence is grossly disturbed. In such cases, cardiac output deteriorates because the contraction of the right and left heart cambers are not synchronized sufficiently to eject blood therefrom.
In patients suffering from congestive heart failure, the hearts become dilated and the conduction and depolarization sequences of the heart chambers may exhibit Intra-Atrial Conduction Defects (IACD), Left Bundle Branch Block (LBBB), Right Bundle Branch Block (RBBB) and Intra Ventricular Conduction Defects (IVCD). Single and dual chamber pacing of the right atrium and/or the right ventricle can be counterproductive in such cases, depending on the defective conduction pathway and the location of the pace/sense electrodes.
A number of proposals have been advanced for providing pacing therapies to alleviate theses conditions and restore synchronous depolarization of right and left, upper and lower, heart chambers. The proposals appearing in U.S. Pat. Nos. 3,937,266, 4,088,140, 4,548,203, 4,458,677 and 4,332,259 are summarized in U.S. Pat. Nos. 4,928,688 and 5,674,259, all incorporated herein by reference. The advantages of providing sensing at pace/sense electrodes located in both the right and left heart chambers are addressed in the '688 and '2
Boute Willem
Van Bolhuis Harm H.
Berry Thomas G.
Getzow Scott M.
Medtronic Inc.
Woods Thomas F.
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