Measuring chronotropic incompetence (CI) in a patient with a unicameral leadless pacemaker, such as the Aveir VR, can be challenging due to the device's single-chamber ventricular pacing mode and lack of atrial sensing or pacing capabilities. However, several methods can be used to assess CI in these patients:
Pacemaker interrogation:
- During pacemaker interrogation, the device's rate-responsive features and settings should be reviewed.
- If the pacemaker has an accelerometer or other activity sensor, the rate response can be evaluated by analyzing the sensor-indicated rate during physical activity.
- If the sensor-indicated rate does not increase appropriately with activity or falls short of the programmed upper sensor rate, it may suggest CI.
Exercise stress test with pacemaker reprogramming:
- Before the exercise stress test, the pacemaker's rate-responsive features can be temporarily reprogrammed to a non-rate-responsive mode (e.g., VVI mode) to assess the patient's intrinsic chronotropic response.
- During the test, the patient's intrinsic heart rate response to exercise is monitored, and the presence of CI is determined based on the criteria mentioned in the previous response (e.g., failure to achieve 85% of age-predicted maximum heart rate).
- After the test, the pacemaker should be reprogrammed to its original settings.
Cardiac contractility modulation (CCM) response:
- Some newer pacemaker systems, such as the Aveir DR leadless pacemaker (currently under development), may incorporate cardiac contractility modulation (CCM) technology.
- CCM is a therapy that delivers non-excitatory electrical signals to the heart during the absolute refractory period to improve cardiac contractility and performance.
- In patients with CCM-capable pacemakers, the contractility response to exercise can be assessed by analyzing the changes in CCM parameters (e.g., CCM amplitude or duration) during physical activity.
- A blunted or inadequate CCM response to exercise may indicate CI.
Symptom assessment and quality of life questionnaires:
- In addition to objective measures, the patient's subjective symptoms and quality of life should be assessed.
- Patients with CI may report symptoms such as fatigue, dyspnea, or reduced exercise tolerance, which can impact their daily activities and overall well-being.
- Standardized questionnaires, such as the Kansas City Cardiomyopathy Questionnaire (KCCQ) or the Minnesota Living with Heart Failure Questionnaire (MLHFQ), can be used to quantify the patient's symptoms and functional status.
Alternative stress testing modalities:
- In some cases, alternative stress testing modalities, such as dobutamine stress echocardiography or nuclear stress testing, may be used to assess the patient's cardiac response to pharmacological stress.
- While these tests do not directly measure chronotropic response, they can provide valuable information about the patient's cardiac function and reserve under stress conditions.
It's important to note that the assessment of CI in patients with unicameral leadless pacemakers should be performed in collaboration with a cardiologist or electrophysiologist experienced in pacemaker management. The interpretation of the findings should take into account the patient's specific pacemaker settings, underlying cardiac condition, and overall clinical context.
If significant CI is identified and is thought to contribute to the patient's symptoms or functional limitations, adjustments to the pacemaker's rate-responsive settings or consideration of alternative pacing modalities (e.g., upgrading to a dual-chamber pacemaker) may be necessary to optimize the patient's chronotropic response and improve their quality of life.
Regular follow-up and monitoring are essential to assess the patient's response to any pacemaker adjustments and to ensure that their pacing therapy remains appropriate for their individual needs and clinical status.
