Method and apparatus for improving cardiac efficiency based on myocardial oxygen consumption
Devices and methods for improving cardiac efficiency involve measuring, patient-internally, an oxygen saturation parameter indicative of oxygen usage of myocardial tissue of the heart. A cardiac electrical therapy is adjusted to cause a change of the measured oxygen saturation parameter, and the adjusted cardiac electrical therapy is selected for delivery based on a changed oxygen saturation parameter indicative of an increase in cardiac efficiency.
1. A method of improving cardiac efficiency, comprising:
measuring, patient-internally in at least one of a coronary vein and the great cardiac vein of the patient's heart, oxygen saturation indicative of oxygen usage of myocardial tissue of the heart;
measuring cardiac stroke volume;
calculating a cardiac efficiency parameter based on the measured oxygen saturation and the measured stroke volume;
adjusting a cardiac electrical therapy to cause a change of the measured oxygen saturation;
calculating a change in the cardiac efficiency parameter resulting from the cardiac electrical therapy adjustment;
determining whether the adjustment in the cardiac electrical therapy decreased or increased cardiac efficiency based on the calculated change in the cardiac efficiency parameter; and
selecting the adjusted cardiac electrical therapy for delivery if the adjustment of the cardiac electrical therapy was determined to increase cardiac efficiency, wherein at least some of the steps of calculating the cardiac efficiency parameter, calculating the change, determining, and selecting are performed at least in part by circuitry.
2. The method of claim 1 , wherein measuring the oxygen saturation comprises measuring the oxygen saturation in the coronary vein of the patient's heart.
3. The method of claim 1 , wherein measuring the oxygen saturation comprises measuring the oxygen saturation in the great cardiac vein of the patient's heart.
4. The method of claim 1 , wherein calculating the change in cardiac efficiency parameter comprises correcting for changes of the measured oxygen saturation due to external work load using the measured stroke volume.
5. The method of claim 1 , wherein determining whether the adjustment of the cardiac electrical therapy decreased or increased cardiac efficiency comprises determining whether oxygen saturation increased or decreased based on the adjustment of the cardiac electrical therapy, the therapy adjustment being determined to increase cardiac efficiency if higher oxygen saturation is measured after the therapy adjustment and the therapy adjustment being determined to decrease cardiac efficiency if lower oxygen saturation is measured after the therapy adjustment.
6. The method of claim 1 , wherein calculating the change in cardiac efficiency parameter comprises computing the patient's cardiac efficiency based on a relationship defined by
(
SV
·
PP
)
(
1
-
O
2
)
,
where SV is the associated stroke volume measurement, PP is the associated pulse pressure measurement, and O2 is the oxygen saturation level measurement.
7. The method of claim 1 , wherein calculating the change in cardiac efficiency parameter comprises computing the patient's cardiac efficiency based on a relationship defined by where
(
SV
·
HR
)
(
1
-
O
2
)
,
SV is the associated stroke volume measurement, HR is the associated heart rate, and O2 is the oxygen saturation level measurement.
8. The method of claim 1 , wherein calculating the cardiac efficiency parameter comprises calculating a first cardiac efficiency by dividing stroke volume by oxygen saturation using stroke volume and oxygen saturation measurements taken before the cardiac electrical therapy adjustment, and wherein calculating the change in cardiac efficiency parameter comprises calculating a second cardiac efficiency by dividing stroke volume by oxygen saturation using stroke volume and oxygen saturation measurements taken after the cardiac electrical therapy adjustment and determining the difference between the first and second cardiac efficiency calculations.
9. The method of claim 1 , wherein the cardiac electrical therapy comprises a pacing therapy.
10. The method of claim 1 , wherein the cardiac electrical therapy comprises a pacing therapy, and adjusting the cardiac electrical therapy comprises adjusting an atrioventricular (A-V) delay of the pacing therapy.
11. The method of claim 1 , wherein the cardiac electrical therapy comprises a pacing therapy, and adjusting the cardiac electrical therapy comprises adjusting a pacing rate of the pacing therapy.
12. The method of claim 1 , wherein the cardiac electrical therapy comprises a pacing therapy, and adjusting the cardiac electrical therapy comprises adjusting a pacing site for the pacing therapy.
13. The method of claim 1 , wherein the cardiac electrical therapy comprises a resynchronization therapy delivered to the heart.
14. The method of claim 1 , wherein the cardiac electrical therapy comprises a bi-ventricular pacing therapy, and adjusting the cardiac electrical therapy comprises adjusting an inter-ventricular delay or an atrioventricular (A-V) delay of the bi-ventricular pacing therapy.
15. The method of claim 1 , wherein processes of claim 1 are repeated until a determination is made that the adjustment in the cardiac electrical therapy decreased cardiac efficiency based on the calculated change in the cardiac efficiency parameter.
16. The method of claim 15 , further comprising selecting a previously adjusted cardiac electrical therapy for delivery if the adjustment of the cardiac electrical therapy was determined to decrease cardiac efficiency.
17. A system for improving cardiac efficiency, comprising:
means for measuring, patient-internally in at least one of a coronary vein and the great cardiac vein of the patient's heart, oxygen saturation indicative of oxygen usage of myocardial tissue of the heart;
means for measuring cardiac stroke volume;
means for calculating a cardiac efficiency parameter based on the measured oxygen saturation and the measured stroke volume;
means for adjusting a cardiac electrical therapy to cause a change of the measured oxygen saturation;
means for calculating a change in the cardiac efficiency parameter resulting from the cardiac electrical therapy adjustment;
means for determining whether the adjustment of the cardiac electrical therapy decreased or increased cardiac efficiency based on the calculated change in the cardiac efficiency parameter; and
means for selecting the adjusted cardiac electrical therapy for delivery if the adjustment of the cardiac electrical therapy was determined to increase cardiac efficiency.
18. The system of claim 17 , wherein means for determining whether the adjustment of the cardiac electrical therapy decreased or increased cardiac efficiency comprises means for determining whether oxygen saturation increased or decreased from the adjustment of the cardiac electrical therapy, the therapy adjustment being determined to increase cardiac efficiency if higher oxygen saturation is measured after the therapy adjustment and the therapy adjustment being determined to decrease cardiac efficiency if lower oxygen saturation is measured after the therapy adjustment.
19. The system of claim 17 , wherein the means for calculating the change in cardiac efficiency comprises means for computing the patient's cardiac efficiency using the measured stroke volume.