Results

Patient characteristics

All patients underwent a successful pacemaker implantation, and there were no complications or deaths 30 days post-procedure. The baseline characteristics of the patients are shown in Table 1 . The mean age was 76 ± 9 years (range 29 to 98 years), and there were 315 males (50.7%). The etiology of the device implantation was identified as atrioventricular block in 307 (49.4%) patients, sick sinus syndrome in 276 (44.4%), atrial fibrillation in 32 (5.2%), and others in the remaining 6 (1.0%). At the time of the device implantation, 583 (93.9%) patients were diagnosed with a grade I disability due to a JCS guideline class I indication. A history of heart failure was noted in 238 (38.3%) patients.

Changes in the functional capacity

The distribution of the FC at baseline, 3 months, 6 months, and 1 year after the pacemaker implantation is shown in Figure 1 . Three months after the pacemaker implantation, 16 patients with a poor FC and 105 with a moderate FC at baseline improved to a good FC (Figure 1A ). However, 3 patients with a moderate FC and 4 with a good FC at baseline deteriorated to a poor FC at 3 months after the implantation. Three months after the pacemaker implantation, the distribution of the three FCs remained at those levels by the end of the follow-up (p=0.18).

Predictors of cardiovascular hospitalizations and all-cause mortality

During a median of 2.4 years of follow-up (interquartile range 0.2 to 3 years), 71 (11%) patients had a cardiovascular hospitalization (heart failure [n=45], ischemic heart disease [n=18], and strokes [n=8]). A total of 35 patients (5.6%) died due to a malignancy (n=8), sepsis (n=7), heart failure (n=6), respiratory failure (n=3), sudden death (n=2), stroke (n=1), or other causes (n=8). The univariate Cox analysis revealed that a history of heart failure and a poor FC were significantly associated with a hospitalization (Table 2 ). The multivariate Cox analysis adjusted for the age, sex, history of heart failure, and a poor FC revealed that a history of heart failure (HR 2.097, 95% CI 1.275-3.448, p=0.004) and a poor FC (HR 2.494, 95% CI 1.227-5.070, p=0.012) remained as independent predictors. For the all-cause death, the age (HR 1.096, 95% CI 1.043-1.151, p<0.001) and a poor FC (HR 3.338, 95% CI 1.254-8.886, p=0.016) were independent predictors after being adjusted for the age, sex, and a poor FC (Table 3 ). The Kaplan-Meier analysis demonstrated that the rate of a hospitalization (Figure 2A ) and the total mortality were significantly higher as the FC decreased (Figure 2B ).

Subgroup analysis of poor functional capacity patients 1 year after the pacemaker implantation

We further examined the outcome of the 40 patients with a poor FC at the time of the pacemaker implantation (Figure. 3A ). Three patients died and 3 were lost to follow-up at 1 year after the device implantation. Of the remaining 34 patients, 8 (20%) had no improvement in the FC, but 7 and 19 patients improved to a moderate FC and a good FC, respectively. Those 34 patients were further followed for a median of 2 years (interquartile range 0.3 to 2 years). The patients that remained with a poor FC one year after the pacemaker implantation had a significantly higher mortality rate (37.5%) than those that improved to a good FC (Figure 3B ).