Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-04-27
2002-11-05
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06477420
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to implantable medical devices and methods for cardiac stimulation. More particularly, the present invention pertains to implantable medical devices and methods that employ mode switching in cardiac stimulation.
BACKGROUND OF THE INVENTION
Generally, in the human heart, the sinus (or sinoatrial (SA) node typically located near the junction of the superior vena cava and the right atrium) constitutes the primary natural pacemaker by which rhythmic electrical excitation is developed. The cardiac impulse arising from the sinus node is transmitted to the two atrial chambers (or atria) at the right and left sides of the heart. In response to excitation from the SA node, the atria contract, pumping blood from those chambers into the respective ventricular chambers (or ventricles). The impulse is transmitted to the ventricles through the atrio-ventricular (AV) node, and via a conduction system comprising the bundle of His, or common bundle, the right and left bundle branches, and the Purkinje fibers. The transmitted impulse causes the ventricles to contract with the right ventricle pumping unoxygenated blood through the pulmonary artery to the lungs and the left ventricle pumping oxygenated (arterial) blood through the aorta and the lesser arteries to the body. The right atrium receives the unoxygenated (venous) blood. The blood oxygenated by the lungs is carried via the pulmonary veins to the left atrium.
The above action is repeated in a rhythmic cardiac cycle in which the atrial and ventricular chambers alternately contract and pump, and then relax and fill. One-way valves, between the atrial and ventricular chambers on the right and left sides of the heart, and at the exits of the right and left ventricles, prevent backflow of the blood as it moves through the heart and the circulatory system. This sinus node is spontaneously rhythmic, and the cardiac rhythm it generates is termed sinus rhythm. This capacity to produce spontaneous cardiac impulse is called rhythmicity. Some other cardiac tissues possess rhythmicity and hence constitute secondary natural pacemakers, but the sinus node is the primary natural pacemaker because it spontaneously generates electrical pulses at a faster rate. The secondary pacemakers tend to be inhibited by the more rapid rate at which impulses are generated by the sinus node.
Disruption of the natural pacemaking and propagation system as a result of aging or disease is commonly treated by artificial cardiac pacing, by which rhythmic electrical discharges are applied to the heart at a desired rate from an artificial pacemaker. A pacemaker is a medical device which delivers electrical pulses to an electrode that is implanted adjacent to or in the patient's heart to stimulate the heart so that it will contract and beat at a desired rate. If the body's natural pacemaker performs correctly, blood is oxygenated in the lungs and efficiently pumped by the heart to the body's oxygen-demanding tissues. However, when the body's natural pacemaker malfunctions, an implantable pacemaker often is required to properly stimulate the heart.
Implantable pacemakers are typically designed to operate using various different response methodologies, such as, for example, nonsynchronous or asynchronous (fixed rate), inhibited (stimulus generated in the absence of a specified cardiac activity), or triggered (stimulus delivered in response to a specific hemodynamic parameter). Generally, inhibited and triggered pacemakers may be grouped as “demand”-type pacemakers, in which a pacing pulse is only generated when demanded by the heart. To determine when pacing is required by the pacemaker, demand pacemakers may sense various conditions such as heart rate, physical exertion, temperature, and the like. Moreover, pacemaker implementations range from the simple fixed rate, single chamber device that provides pacing with no sensing function, to highly complex models that provide fully-automatic dual chamber pacing and sensing functions. For example, such multiple chamber pacemakers are described in U.S. Pat. No. 4,928,688 to Mower entitled “Method and Apparatus for Treating Hemodynamic Dysfunction,” issued May 29, 1990; U.S. Pat. No. 5,792,203 to Schroeppel entitled “Universal Programmable Cardiac Stimulation Device,” issued Aug. 11 , 1998; U.S. Pat. No. 5,893,882 to Peterson et al. entitled “Method and Apparatus for Diagnosis and Treatment of Arrhythmias,” issued Apr. 13, 1999; and U.S. Pat. No. 6,081,748 to Struble et al. entitled “Multiple Channel, Sequential Cardiac Pacing Systems,” issued Jun. 27, 2000.
Because of the large number of options available for pacer operation, an industry convention has been established whereby specific pacer configurations are identified according to a code comprising multiple letters (generally, three to four letters, although a fifth coded position may also be used). The most common configuration codes comprise either three or four letters, as shown in Table I below. For simplicity, the fifth coded position is omitted. Each code can be interpreted as follows:
TABLE I
Code Position
1
2
3
4
function
chamber
chamber
response to
programmability
identified
paced
sensed
sensing
rate modulation
options
0 - none
0 - none
0 - none
0 - none
available
A - atrium
A - atrium
T - triggered
P - programmable
V - ventricle
V - ventricle
I - inhibited
M - multi-
D - dual
D - dual
D - dual
programmable
(A + V)
(A + V)
(T + I)
C - communi-
cating
R - rate
modulating
For example, a DDD pacer paces either chamber (atrium or ventricle) and senses in either chamber. Thus, a pacer in DDD mode, may pace the ventricle in response to electrical activity sensed in the atrium. A VVI pacer paces and senses in the ventricle, but its pacing is inhibited by spontaneous electrical activity of the ventricle, also referred to as intrinsic ventricular activity (i.e., the ventricle paces itself naturally). In VVIR mode, ventricle pacing is similarly inhibited upon determining that the ventricle is naturally contracting. With the VVIR mode, the pacer's pacing rate, however, in the absence of naturally occurring pacing, is modulated by the physical activity level of the patient. Pacers commonly include accelerometers to provide an indication of the patient's level of physical activity.
As illustrated in the table above, it may be desirable to sense in one cardiac chamber (e.g., detect electrical activity represented of contraction of the chamber and referred to as a “sensed event”) and, in response, pace (referred to as a “paced event”) in the same or different chamber. It also may be desirable to pace at two electrode locations following a sensed event. For example, patients with abnormally fast atrial rhythms (referred to as atrial tachyarrhythmias) are often treated with pacemakers that include an electrode in each of the two atrial chambers and a third electrode in the right ventricle. Both atrial chambers usually are paced following a sensed event in either chamber. Various pacemaker protocols may be used.
Further, for example, some patients, like heart failure patients, are often treated with bi-ventricular pacemakers that include an electrode in each of the two ventricular chambers, and also possible a third electrode in the right atrium. Both ventricular chambers usually are paced following a sensed or paced atrial event.
In the context of dual chamber pacing, a variety of mode switching features have been developed which detect an excessively rapid atrial rhythm and in response cause the pacemaker to switch from an atrial synchronized pacing mode such as DDD to a nonsynchronized mode such as VVI or DDI. Such mode switching features are disclosed in U.S. Pat. No. 5,144,949 to Olson entitled “Dual Chamber Rate Responsive Pacemaker With Automatic Mode Switching,” issued Sep. 8, 1992; U.S. Pat. No. 5,318,594 to Limousin et al. entitled “DDD Type Cardiac Pacemaker Having Automatic Operating Mode Switching,” issued Jun. 7, 1994; U.S. Pat. No. 4,944,298 to Sholder entitled “Atrial
Dunham David
Struble Chester L.
Berry Tom G.
Getzow Scott M.
Medtronic Inc
Waldkoette Eric R.
Woods Thomas F.
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