Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Series A Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Series C Convertible Preferred Stock [Member]	Series D Convertible Preferred Stock [Member]
Beginning balances at Dec. 31, 2018						$ 3,059	$ 40,685	$ 74,575
Beginning balances, Shares at Dec. 31, 2018						388,558	3,088,444	4,499,921
Beginning balances at Dec. 31, 2018	$ (131,824)	$ 1	$ 30,150	$ (161,995)	$ 20
Beginning balances, Shares at Dec. 31, 2018		656,654
Unrealized (loss) gain on marketable securities	46				46
Foreign currency translation adjustment	(96)				(96)
Issuance of Series A preferred stock for cashless warrant exercise						2,652
Issuance of Series D convertible preferred stock for cash, net of issuance costs									$ 66,563
Issuance of Series D convertible preferred stock for cash, net of issuance costs, Shares									4,091,819
Issuance of Series D convertible preferred stock for 2018 Convertible Notes and 2019 Convertible Notes									$ 68,476
Issuance of Series D convertible preferred stock for 2018 Convertible Notes and 2019 Convertible Notes, Shares									4,108,478
Stock-based compensation	2,994		2,994
Stock-based compensation, shares		11,449
Stock option exercises	108		108
Stock option exercises, shares		27,799
Net loss	(97,039)			(97,039)
Ending balances at Dec. 31, 2019						$ 3,059	$ 40,685	$ 74,575	$ 135,039
Ending balances, shares at Dec. 31, 2019						391,210	3,088,444	4,499,921	8,200,297
Ending balances at Dec. 31, 2019	(225,811)	$ 1	33,252	(259,034)	(30)
Ending balances, shares at Dec. 31, 2019		695,902
Unrealized (loss) gain on marketable securities	(53)				(53)
Foreign currency translation adjustment	363				363
Issuance of Series D convertible preferred stock for the Biotronik Asset Purchase									$ 5,000
Issuance of Series D convertible preferred stock for the Biotronik Asset Purchase, Shares									273,070
Issuance of Series D convertible preferred stock for the contingent consideration related to the Rhythm Xience Acquisition									$ 2,197
Issuance of Series D convertible preferred stock for the contingent consideration related to the Rhythm Xience Acquisition, Shares									119,993
Conversion of convertible preferred stock into common stock upon IPO	260,555	$ 17	260,538			$ (3,059)	$ (40,685)	$ (74,575)	$ (142,236)
Conversion of convertible preferred stock into common stop upon IPO, shares		16,572,935				(391,210)	(3,088,444)	(4,499,921)	(8,593,360)
Issuance of common stock for cash, net of issuance costs of $16,361	166,286	$ 10	166,276
Issuance of common stock for cash, net of issuance cost of $16,361, shares		10,147,058
Reclassification of warrant liability to stockholders' equity	14,474		14,474
Stock-based compensation	12,103		12,103
Stock-based compensation, shares		319,420
Stock option exercises	634		634
Stock option exercises, shares		124,938
Warrant exercise	13		13
Warrant exercise, Shares		131,172
Net loss	(101,981)			(101,981)
Ending balances, shares at Dec. 31, 2020						0	0	0	0
Ending balances at Dec. 31, 2020	$ 126,583	$ 28	$ 487,290	$ (361,015)	$ 280
Ending balances, shares at Dec. 31, 2020		27,991,425