9-07: Feasibility of Extravascular Pacing with a Novel Substernal Electrode Configuration: Results from the Multi-center Substernal Pacing Acute Clinical Evaluation (SPACE) Trial
Bibliographic record
Abstract
Purpose: Subcutaneous defibrillators offer a viable alternative to intravascular transvenous defibrillators. However, because of extra-thoracic lead placement, this system is limited by high defibrillation thresholds and an inability to deliver anti-tachycardia pacing. The SPACE trial evaluated the feasibility of cardiac pacing from an extra-vascular substernal space. Method: This prospective feasibility study enrolled adult patients (pts) undergoing midline sternotomy surgery or S-ICD implant. The primary endpoint was to assess the feasibility of pacing through a decapolar EP catheter (Marinr, 7F, Medtronic) temporarily placed via percutaneous subxiphoid access into the mediastinal tissues under the sternum at or adjacent to the midline. Using fluoroscopy and a malleable tunneling tool and introducer, the middle pair of electrodes was centered over the right ventricle. Pacing capture data in 7 vectors (3 bipolar and 4 unipolar) were collected with constant current pacing up to 20 mA and pulse-width (PW) up to 10 ms. Summary of Results: Twenty-six pts (21 males, 5 females; age 64.4 ± 10.0 years) were studied at 8 sites in the US and Canada. Parent procedures included one S-ICD implantation and 25 cardiothoracic surgeries. Catheter placement was accomplished in all 26 pts (mean placement time = 11.7 ± 10.1 minutes). Eighteen out of 26 pts had successful, consistent ventricular pacing capture (PC) in ≥ 1 tested vector. The mean pacing thresholds at PW 10 ms, 3 ms, 1 ms were 7.3 ± 4.2 mA (18 pts), 9.0 ± 4.7 mA (13 pts), 11.8 ± 4.5 mA (7 pts), respectively. Failed PC in 8 pts was mostly associated with sub-optimal implant or atrial PC. Among the 18 pts with PC, 10 pts had the best PC in bipolar vs 7 pts in unipolar (no difference in 1 pt). Among the 16 pts with bipolar PC, widely spaced bipolar electrode pairs were consistently associated with the lowest threshold in all pts. For the 16 pts with bipolar PC with electrode spacing 19 mm and 10 ms PW, the median pacing threshold was 3.0 V (IQR: 2.3-8.1 V) or 4.2 mA (IQR: 3.0-10.5 mA). Conclusion: Preliminary data demonstrates that pacing is feasible from this novel extravascular substernal location. A bipolar substernal electrode configuration with wide electrode spacing has the potential to provide pacing in a future extravascular defibrillator.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".