New and combined sensors for adaptive-rate pacing

Minute ventilation sensor-driven rate response as a part of cardiac resynchronization therapy optimization in older patients

BACKGROUND

Chronotropic incompetence (CI) is common among elderly cardiac resynchronization therapy pacemaker (CRT-P) patients on optimal medical therapy. This study aimed to evaluate the impact of optimized rate-adaptive pacing utilizing the minute ventilation (MV) sensor on exercise tolerance.

METHODS

In a prospective, multicenter study, older patients (median age 76 years) with a guideline-based indication for CRT were evaluated following CRT-P implantation. If there was no documented CI, requiring clinically rate-responsive pacing, the device was programmed DDD at pre-discharge. At 1 month, a 6-min walk test (6MWT) was conducted. If the maximum heart rate was < 100 bpm or < 80% of the age-predicted maximum, the response was considered CI. Patients with CI were programmed with DDDR. At 3 months post-implant, the 6MWT was repeated in the correct respective programming mode. In addition, heart rate score (HRSc, defined as the percentage of all sensed and paced atrial events in the single tallest 10 bpm histogram bin) was assessed at 1 and 3 months.

RESULTS

CI was identified in 46/61 (75%) of patients without prior indication at enrollment. MV sensor-based DDDR mode increased heart rate in CI patients similarly to non-CI patients with intrinsically driven heart rates during 6MWT. Walking distance increased substantially with DDDR (349 ± 132 m vs. 376 ± 128 m at 1 and 3 months, respectively, p < 0.05). Furthermore, DDDR reduced HRSc by 14% (absolute reduction, p < 0.001) in those with more severe CI, i.e., HRSc ≥ 70%.

CONCLUSION

Exercise tolerance in older CRT-P patients can be further improved by the utilization of an MV sensor.

Chronotropic Incompetence in Chronic Heart Failure

Chronotropic incompetence (CI) is generally defined as the inability to increase the heart rate (HR) adequately during exercise to match cardiac output to metabolic demands. In patients with heart failure (HF), however, this definition is unsuitable because metabolic demands are unmatched to cardiac output in both conditions. Moreover, HR dynamics in patients with HF differ from those in healthy subjects and may be affected by β-blocking medication. Nevertheless, it has been demonstrated that CI in HF is associated with reduced functional capacity and poor survival. During exercise, the normal heart increases both stroke volume and HR, whereas in the failing heart, contractility reserve is lost, thus rendering increases in cardiac output primarily dependent on cardioacceleration. Consequently, insufficient cardioacceleration because of CI may be considered a major limiting factor in the exercise capacity of patients with HF. Despite the profound effects of CI in this specific population, the issue has drawn limited attention during the past years and is often overlooked in clinical practice. This might partly be caused by a lack of standardized approach to diagnose the disease, further complicated by changes in HR dynamics in the HF population, which render reference values derived from a normal population invalid. Cardiac implantable electronic devices (implantable cardioverter defibrillator; cardiac resynchronization therapy) now offer a unique opportunity to study HR dynamics and provide treatment options for CI by rate-adaptive pacing using an incorporated sensor that measures physical activity. This review provides an overview of disease mechanisms, diagnostic strategies, clinical consequences, and state-of-the-art device therapy for CI in HF.

Pacemaker automaticity

The automated measurement of the main electrical parameters of pacemakers, such as battery voltage, current drain, pacing impedance, sensing levels, and pacing thresholds enables a continuous monitoring of the adequate functioning of the implanted device. New technologies in device interrogation, data transfer, and patient alert functions will enhance therapy safety significantly by the immediate detection of all, including transient, device malfunctions. The introduction of this technology will result in major changes in follow-up of patients with pacemakers. Technically we are very close to the goal of a fully automated pacemaker, although clinical acceptance lags behind. Clinical studies are necessary to demonstrate the beneficial effects of automated device functions, with regard to the main rationales for pacemaker automatization: increased patient safety, improved quality of life, and an improvement in the cost-benefit ratio in pacemaker therapy.

Evaluation of a dual sensor rate responsive pacing system based on a new concept. French Talent DR Pacemaker Investigators

The minute ventilation is known to be one of the most physiological indicators of exercise. A curvilinear relationship between VE and the normal sinus rhythm (NSR) has been demonstrated in healthy patients. The aim of this study is to show that a pacemaker based on a VE sensor can reproduce such a relationship. Eighty-one patients received a Talent DR 213 (ELA Medical, Montrouge, France) pacemaker with a third-generation rate responsive algorithm. At 1-month follow-up, the patients underwent a treadmill exercise test, after which three groups were defined: group 1 had 6 patients who were 100% paced throughout the exercise test; group 2 had 10 patients who maintained NSR throughout the test; and group 3 had 12 patients who had cardiopulmonary recording during the exercise test. In group 1 patients, the simulation function computed the simulated rate (sim-rate), which was compared to the sensor-driven rate (SDR). In group 2 patients, sim-rate was compared to the NSR. In group 3 patients, cardiac and metabolic reserves were compared to determine the appropriateness of the rate response to exercise (HRR% vs MR%). The results showed that the mean correlation coefficient between sim-rate and SDR was 0.983 +/- 0.005 (P < 0.001); the mean correlation coefficient between NSR and SDR was 0.92 +/- 0.07 (P < 0.001); and a linear relationship was found between HRR% and MR%, with a mean slope of 1.1 +/- 0.2 that was significantly equal to the theoretical value of 1 (P = NS). In conclusion, combining an activity-driven sensor with a physiological sensor allows the preservation of a physiological rate response during exercise.

Permanent cardiac pacemakers in the elderly

OBJECTIVE

To review (1) Changes in cardiac impulse generation, conduction, and ventricular filling in normal aging and disease; (2) Pacemaker technology and nomenclature; (3) Expert guidelines about pacemaker use; (4) Studies of pacemaker effectiveness and utilization.

DESIGN

Articles were identified through a Medline search, review of articles' bibliographies, and contact with pacemaker manufacturer representatives for information on device features and costs. These articles were reviewed, and the relevant data are presented.

RESULTS

Abnormalities in impulse generation and conduction are common in the elderly. Pacemaker use is higher in the elderly than in other population groups. Hemodynamic changes associated with aging include an increased contribution of atrial contraction to ventricular filling. Pacemakers, which maintain the synchrony between the atria and ventricles, may be particularly advantageous in the elderly for this reason. Rate-responsive ventricular pacemakers improve the quality of life compared with fixed rate devices in some patients over the age of 75. Dual-chamber, sequential pacemakers are more likely to reduce symptoms of pacemaker syndrome than ventricular pacemakers and probably also prolong survival and reduce risk of atrial fibrillation in certain groups of patients. However, dual chamber devices are more expensive and require more frequent follow-up. Pacemaker utilization can vary widely by region. Decisions about pacemakers require explicit tradeoffs between risk and quality of life on one hand and cost on the other. In many clinical situations, there is controversy as to whether pacemakers should be used.

CONCLUSIONS

Pacemakers provide definite benefits to some patients, whereas in others, the likelihood of benefit is uncertain. More sophisticated devices may provide some additional benefit, but they are more costly. Further data is still required to define precisely which groups of patients substantially benefit from complex and expensive pacing modalities compared with simpler ones.