DISCUSSION
Our main results are the following: 1) permanent LPM implantation in patients hospitalized in intensive care unit is feasible in 98% of cases; 2) procedure-related complications are <5% in this very high-risk population, with a virtually null risk of infection.
Pacemaker implantation in ICU patients is associated with several challenging issues. Venous access is often limited due to the presence of central venous lines for perfusion or hemodialysis or hemofiltration [7,8]. In our series, 3 patients had no suitable supracaval venous access for conventional pacemaker implantation. The alternative is cardiac surgery with an epicardial approach, which appears highly invasive in this critically ill population. The infectious risk is also a major issue, amplified by multiple central venous lines, mechanical ventilation, and ongoing sepsis or bacteremia [9-11]. More than half of our patients were actually under intravenous antibiotherapy.
When atropine bolus or isoproterenol infusion are not sustainable options, implantation of a temporary pacemaker is usually performed, before considering PPM [12]. TTP is associated with a high rate of complications [13]. In the US national database, pneumothorax, pericardial tamponade and non-pericardial bleeding were found in 0.6, 0.9 and 2.4% of patients, respectively [14]. In a more recent review of the literature, the total rate of complications related to TTP ranged from 23% (in the 2010s decade, 5.7% considered serious complications) to 43% (in the 1980s, 16.5% serious), including 2% of complicated access, 1.6% of cardiac perforation, near 5% of infections, and more than 20% of device complications [2]. TTP also prolongs hospitalization with a mean of 11 days.
Patients hospitalized in ICU and requiring prolonged cardiac pacing are frail and severe. Bradycardia <40 beats-per-minute adds 4 points to the APACHE II and 11 points to the SAPS II scores. In our cohort, median Charlson comorbidity index was as high as 7 and in-hospital mortality as low as 6%, as compared with a median score of 2 and an in-hospital mortality rate of 18% in a study by Christensen and colleagues, although these 2 ICU populations cannot be directly compared [15-17].
In that respect, LPM implantation is appealing. The Micra LPM is a small 0.8 cubic centimeter device, weighing barely 2 grams, implanted through a femoral approach on the right ventricular septum (Figure 2 ). The femoral approach solves the potential issues regarding supracaval venous access, and the risk of device-related infection is virtually nil, even in high-risk populations [6,18]. In our series, 60% of patients had ongoing sepsis or documented bacteremia, of whom 92% were under antibiotherapy, and no device infection occurred. Moreover, the risk of dislodgement or pacing issue is extremely rare (<1%) [19], to be compared with a risk of ~20% with TTP [2]. The main issue with LPM is the risk of acute cardiac injury, 4% in our series, as compared with a less than 1% reported rate in the literature [18]. This can be easily explained by the frailty and multiple comorbidities of the ICU population. This risk could be further decreased by positioning the device on the right ventricular septum rather than at the apex, and with regular appropriate training [19].
The alternative to implant an active fixation lead connected to an external re-sterilized pulse generator has also been shown to be associated with a very low risk of complications, while being a removable system [20]. However, this technique requires suitable supracaval access and could not have been offered in up to 3% of our patients.