Medical History:
Mrs. JD is a 64 yr old African American referred to cardiac rehabilitation 6 wk following implantation of a DDDR pacemaker with a vibration sensor. The indication for the pacemaker was marked sinus bradycardia and chronotropic incompetence. Her primary complaints were episodes of shortness of breath, undue fatigue, light-headedness, and weakness at rest and during exertion. She had no other significant cardiac history except for mild hypertension. Mrs. JD also has mild arthritis in her hands and knees. Her body mass index is 29. Currently, her symptoms at rest are resolved, but she complains of early exertional fatigue and shortness of breath while doing housework and taking short walks in her neighborhood. Her resting heart rate is paced at 60 beats · min–1.
Exercise Testing Results:
Because of limited exercise tolerance, Mrs. JD was referred to her cardiologist for a pacemaker evaluation. Her physician administered an office-based walking protocol during which Mrs. JD complained of shortness of breath after 3 min of “brisk” walking. Her heart rate reached a peak of 102 beats · min–1. The diagnosis was that her increase in heart rate was inadequate for the amount of work being performed. As a result, the pacemaker was programmed to a maximum tracking rate of 110 beats · min–1 and a maximum sensor rate of 130 beats · min–1, and the threshold of the sensor was lowered to be more sensitive to body movements.
Exercise Prescription:
The pacemaker settings relevant to her exercise prescription were a lower rate limit of 60 beats · min–1, a programmed maximum tracking rate to 110 beats · min–1, and a programmed sensor rate to 110 beats · min–1. Mrs. JD was given a standard exercise prescription consisting primarily of stationary cycling for 15 min and walking on a treadmill for 15 min. Exercises with handheld weights and flexibility exercises were prescribed for warm-up. Because she did not have an exercise stress test before starting the cardiac exercise program, her exercise intensity for aerobic exercise was set at 12 to 14 on the Borg RPE scale.
Response to Initial Exercise Training Session:
On the stationary cycle, Mrs. JD complained of shortness of breath and early fatigue, stopping at 4 min. Her heart rate peaked at 75 beats · min–1. On the treadmill, she was able to walk for 10 min at 1.5 mph (2.4 kph), reaching a peak heart rate of 98 beats · min–1. Her main complaint was shortness of breath.
Discussion:
In cardiac rehabilitation, the exercise prescription was changed to two bouts of 15 min each of treadmill walking with 2 min rest between bouts. The warm-up was unchanged. Mrs. JD tolerated 2.0 mph (3.2 kph) at 0% grade on the treadmill as prescribed, reporting only mild leg fatigue and shortness of breath. Her peak heart rate reached 122 beats · min–1. In many instances, the pacemaker default factory settings are used. In this case, observation of the patient in cardiac rehabilitation resulted in a referral to her cardiologist, who performed an exercise test; this showed that the pacemaker needed to be reprogrammed to allow for a higher heart rate response, which in turn resulted a greater increase in cardiac output during exercise training. As a result, the patient was better able to meet her exercise training targets in cardiac rehabilitation with a marked reduction in symptoms.
Questions:
1. Why was the maximum tracking rate left unchanged when the pacemaker settings were adjusted?
2. Why was stationary cycling dropped as an exercise modality for this patient?
3. What would be the initial choice for progressing the exercise intensity on the treadmill as the patient improves her fitness—an increase in speed, an increase in grade, or both?
