Clinical studies related to cardiac pacing have shown that an optimal atrio-ventricular pacing delay (e.g., AV delay or PV delay) and/or an optimal interventricular pacing delay (e.g., VV delay) can improve cardiac performance. However, such optimal delays depend on a variety of factors that may vary over time. Thus, what is “optimal” may vary over time. An optimization of AV/PV pacing delay and/or VV pacing delay may be performed at implantation and, in some cases, a re-optimization may be performed during a follow-up consultation. While optimization procedures are beneficial, the benefits may not last due to changes in various factors related to device and/or cardiac function. Accordingly, techniques have been developed for periodically re-optimizing pacing delays. Periodic re-optimization is particularly important when providing CRT. Briefly, CRT seeks to normalize asynchronous cardiac electrical activation and resultant asynchronous contractions associated with heart failure by delivering synchronized pacing stimulus to both ventricles. The stimulus is synchronized so as to improve overall cardiac function. This may have the additional beneficial effect of reducing the susceptibility to life-threatening tachyarrhythmias. Pacemakers and ICDs can be equipped to deliver CRT. Standalone CRT devices can also be provided for implant within patients. By periodically re-optimizing CRT, its operation can be adjusted to respond to the needs of the patient.
The following patents and patent applications set forth various systems and methods for allowing a pacemaker, ICD, CRT device or other cardiac rhythm management (CRM) device to determine and/or adjust AV/PVNV pacing delays so as to help maintain the pacing delays at preferred or optimal values: U.S. Pat. No. 7,590,446; U.S. Published Patent Application 2009/0299423A1; U.S. patent application Ser. No. 11/952,743 (abandoned), filed Dec. 7, 2007, entitled “Systems and Methods for Determining Optimal Atrioventricular Pacing Delays using either Paced or Sensed Atrial Beats”; U.S. patent application Ser. No. 12/328,605, filed Dec. 4, 2008, issued as U.S. Pat. No. 8,442,634, entitled “Systems and Methods for Controlling Ventricular Pacing in Patients with Long Intra-Atrial Conduction Delays”; U.S. patent application Ser. No. 12/507,646, filed Jul. 22, 2009, issued as U.S. Pat. No. 8,265,755, of Min et al. entitled “Systems and Methods for Optimizing Ventricular Pacing Delays for use with Multi-Pole Leads”; U.S. patent application Ser. No. 12/639,881 (pending), filed Dec. 16, 2009, of Min et al., entitled “Systems and Methods for Determining Ventricular Pacing Sites for use with Multi-Pole Leads”; U.S. patent application Ser. No. 12/604,280, filed Oct. 22, 2009, issued as U.S. Pat. No. 8,145,311, of Min et al., entitled “Systems and Methods for Determining Optimal Electrode Pairs for use in Biventricular Pacing using Multi-Pole Ventricular Leads”; and U.S. patent application Ser. No. 12/957,142 (pending), filed Nov. 30, 2010, of Min, entitled “Systems and Methods for Determining Optimal Atrioventricular Pacing Delays based on Cardiomechanical Delays ”. See, also, U.S. Pat. No. 7,248,925, to Bruhns et al., entitled “System and Method for Determining Optimal Atrioventricular Delay based on Intrinsic Conduction Delays.” At least some of the techniques are implemented within the QuickOpt™ systems of St. Jude Medical.
In particular, techniques were set forth within at least some of these patent documents for exploiting various inter-atrial and interventricular conduction delays observed within an intracardiac electrogram (IEGM) to determine preferred or optimal AV/PV/VV pacing delays. In at least some examples, the implanted device (or an external programming device in communication with the implanted device) performs a series of tests to determine intrinsic AV/PV and VV conduction delays from which preferred pacing delays are determined. In particular, an “A sense” test is performed to detect intra-atrial conduction delays from which preferred IEGM-based AV/PV pacing delays are determined. A “V sense” test is performed to detect intrinsic ventricular events from which an intrinsic interventricular conduction delay (Δ) is determined. An “RV pace” test and a separate “LV pace” test are performed to detect paced interventricular conduction delays (IVCD_RL and IVCD_LR, respectively) from which an intrinsic interventricular correction term (ε) is determined. The optimal IEGM-based VV delay is then set based on Δ and ε. In some examples, a pacing latency correction term is applied during the determination of PV. Other examples extend these techniques for use with multi-site LV (MSLV) pacing.
Although these “IEGM-based” techniques are useful, there remains room for further improvement, particularly in terms of the capability of the techniques to identify values for AV/PV/VV pacing delays that optimize or improve cardiac output or stroke volume. It is known that LV dP/dt is a good surrogate for contractility and stroke volume. It has been found that that certain features of impedance signals (Z) measured between the device housing (can) and an electrode in the superior vena cava (SVC) correlate closely with LV dP/dt, at least in animal test subjects. Hence, it would be desirable to exploit SVC-can Z signals or other appropriate Z signals to improve the optimization of pacing delays and it is to this end that aspects of the present invention are generally directed. It would be particularly desirable to provide techniques that allow for Z signals to be exploited for optimization that do not require a large number of optimization tests and it is to this end that some particular aspects of the invention are directed.