Cardiac pacer which compensates for effects of abrupt changes in heart rate
First Claim
1. A method of preventing tachycardia comprising the steps of:
- selecting threshold value for a change in heart cycle length from one heart cycle to a subsequent heart cycle;
selecting a time period, which is longer than the subsequent heart cycle;
measuring heart cycle lengths of an animal;
deriving a change in the heart cycle length from one heart cycle to a subsequent heart cycle;
comparing the change in the heart cycle length to the threshold value to detect when the heart cycle length decreases;
detecting when a new heart beat fails to occur within the time period which commences after the subsequent heart cycle;
if a new heart beat fails to occur within the time period after the change in heart cycle length exceeds the threshold value, commence treating the animal with a cardiac pacing technique to prevent tachycardia from occurring.
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Abstract
Clinical studies of heart patients have demonstrated that ventricular tachyarrhythmia often is preceded by a foreshortened cardiac cycle length followed by a relatively long compensatory pause, thus producing in an abrupt short-to-long cycle length change. An implantable apparatus for preventing tachyarrhythmia measures the cardiac cycle length and detects the occurrence of a foreshortened cardiac cycle length more than a predefined amount between consecutive cycles. When a normal heart beat does not occur within a predefined period of time after such an abrupt change in cycle length, the resulting compensatory pause is eliminated by a cardiac pacer applying an appropriately timed electrical pulse to produce a contraction of the heart. The apparatus also includes a defibrillator to shock the heart in the event that the preventive pacing is not effective.
47 Citations
19 Claims
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1. A method of preventing tachycardia comprising the steps of:
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selecting threshold value for a change in heart cycle length from one heart cycle to a subsequent heart cycle; selecting a time period, which is longer than the subsequent heart cycle; measuring heart cycle lengths of an animal; deriving a change in the heart cycle length from one heart cycle to a subsequent heart cycle; comparing the change in the heart cycle length to the threshold value to detect when the heart cycle length decreases; detecting when a new heart beat fails to occur within the time period which commences after the subsequent heart cycle; if a new heart beat fails to occur within the time period after the change in heart cycle length exceeds the threshold value, commence treating the animal with a cardiac pacing technique to prevent tachycardia from occurring. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An apparatus for preventing tachycardia in a heart of an animal, said apparatus comprising:
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a cardiac pacer which responds to a control signal by applying an electrical pulse to the animal to contract the heart; a mechanism that measures the cardiac cycle length; a detector coupled to said mechanism to produce a first indication when the cardiac cycle length decreases more than a predefined amount from one cycle to a subsequent cycle; a processor which responds to the first indication by producing a second indication when a new heart beat fails to occur within a predefined time period after the subsequent cycle, where the predefined time period is longer than the subsequent cycle; and an evaluator that responds to the second indication by sending the control signals to the cardiac pacer to perform a cardiac pacing technique to prevent tachycardia from occurring. - View Dependent Claims (14, 15, 16)
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17. A method of preventing tachycardia comprising:
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measuring a first length of a first heart cycle; measuring a second length of a second heart cycle which occurs after the first heart cycle; determining when the second length is shorter than the first length by at least a predefined amount; deriving a time period as a function of the second length, where the time period is longer than the second length; detecting when a new heart beat fails to occur within the time period following the second heart cycle and in response thereto producing an indication of such occurrence; and responding to the indication by commencing treatment of the animal with a cardiac pacing technique to prevent tachycardia from occurring. - View Dependent Claims (18, 19)
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Specification