Cardiac Risk Assessment
In a system for assessing cardiac risk of a patient, a measuring component measures a cardiac signal comprised of multiple cardiac cycles at multiple periods in time. A processing component calculates sensitivity of cardiac function to sympathetic drive at each of the periods in time from the measured cardiac signal. A risk identification component evaluates a trend of the sensitivity over time as an indicator of a degree of cardiac risk.
1 . A system for assessing cardiac risk of a patient, the system comprising:
a measuring component that measures a cardiac signal comprised of multiple cardiac cycles at multiple periods in time;
a processing component that calculates sensitivity of cardiac function to sympathetic drive at each of the periods in time from the measured cardiac signal; and
a risk identification component that evaluates a trend of the sensitivity over time as an indicator of a degree of cardiac risk.
2 . The system of claim 1 , wherein the risk identification component evaluates the trend by evaluating a plot of the sensitivity versus time.
3 . The system of claim 1 , wherein the risk identification component evaluates the trend by comparing the trend with a predetermined threshold.
4 . The system of claim 1 , wherein the measuring component, the processing component, and the risk identification component reside in an implantable device.
5 . The system of claim 1 , wherein the measuring component resides in an implantable device, and wherein the processing component and the risk identification component reside in an external device.
6 . The system of claim 5 , further comprising a first telemetry component that resides in the implantable device and a second telemetry component that resides in the external device, wherein the first telemetry component transmits at least a portion of the cardiac signal for receipt by the second telemetry component.
7 . The system of claim 1 , wherein the cardiac function is indicated by an altemans burden over a selected period of time, the alternans burden determined from the cardiac signal.
8 . The system of claim 7 , wherein the alternans burden is a repolarization altemans burden.
9 . The system of claim 7 , wherein the alternans burden is a mechanical altemans burden.
10 . The system of claim 7 , wherein the alternans burden is a QRS altemans burden.
11 . The system of claim 7 , wherein the sensitivity of cardiac function is calculated by computing a ratio of change in the altemans burden to change in a sympathetic tone marker.
12 . The system of claim 7 , wherein the sensitivity of cardiac function is calculated as an onset value of a sympathetic tone marker at which a sustained elevation in the altemans burden appears.
13 . The system of claim 1 , wherein the cardiac function is indicated by a hypertension burden over a selected period of time, the hypertension burden determined from the cardiac signal.
14 . The system of claim 13 wherein the hypertension burden is elevated diastolic blood pressure.
15 . The system of claim 13 wherein the hypertension burden is elevated systolic blood pressure.
16 . The system of claim 1 , wherein sympathetic drive is estimated from a heart rate variability measurement determined from the cardiac signal.
17 . The system of claim 1 , wherein sympathetic drive is estimated from a heart rate increase measurement determined from the cardiac signal.
18 . The system of claim 1 , wherein the cardiac signal is an electrocardiogram signal.
19 . The system of claim 1 , wherein the cardiac signal is an electrogram signal measured using an intracardiac lead.
20 . The system of claim 1 , wherein the cardiac signal is a blood pressure signal.
21 . The system of claim 1 , wherein the cardiac signal is an impedance measurement.
22 . The system of claim 1 , wherein the processing component further calculates a baroreflex sensitivity value from the measured cardiac signal.
23 . The system of claim 22 , wherein an indication of heart rate turbulence, determined from the cardiac signal, indicates the baroreflex sensitivity value.
24 . The system of claim 23 , wherein the indication of heart rate turbulence is a turbulence slope value.
25 . The system of claim 23 , wherein the indication of heart rate turbulence is a turbulence onset value.
26 . The system of claim 1 , wherein the risk identification component adjusts the trend based on circadian variability
27 . The system of claim 1 , wherein the risk identification component filters the trend to remove circadian variability and short term variability.
28 . The system of claim 1 , wherein the trend of the sensitivity over time indicates a degree of cardiac risk that exceeds an expected degree of cardiac risk because of patient non-compliance with a prescribed therapy.
29 . The system of claim 1 , wherein the trend of the sensitivity over time indicates a degree of cardiac risk that exceeds an expected degree of cardiac risk because of insufficient therapy effectiveness.
30 . A method of monitoring effect of a cardiovascular therapy for a patient; the method comprising:
receiving physiologic signal data associated with multiple cardiac cycles;
calculating sensitivity of cardiovascular function to sympathetic drive using the received physiologic signal data;
trending the computed sensitivity over time; and
comparing the sensitivity trend to an expected trend, the expected trend based on a previous condition of the patient and a prescribed therapy regimen that specifies the cardiovascular therapy.
31 . The method of claim 30 , wherein the cardiovascular therapy modulates the effect of the sympathetic tone on cardiac function.
32 . The method of claim 30 , wherein the cardiovascular therapy modulates vascular tone.