St Marys - EPSG:5749

WKT

VERTCS["St_Marys", 
	VDATUM["St_Marys"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["St_Marys", 
	VDATUM["St_Marys"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "5749"]]

Data from @esri/proj-codes

{
  "wkid": 5749,
  "latestWkid": 5749,
  "macro": "PE_VCS_ST_MARYS",
  "name": "St_Marys",
  "wkt": "VERTCS[\"St_Marys\",VDATUM[\"St_Marys\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"St_Marys\",VDATUM[\"St_Marys\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"5749\"]]",
  "description": "St Marys",
  "authority": "EPSG",
  "version": "6.15(9.3.0.0)",
  "deprecated": "no",
  "areaname": "UK - Scilly Isles onshore",
  "extent": {
    "slat": 49.86,
    "nlat": 49.99,
    "llon": -6.41,
    "rlon": -6.23
  }
}