In Crawford v. Washington, 541 U.S. 36 (2004), the Supreme Court revamped the jurisprudence of the Confrontation Clause along "original understanding" lines -- what the right of confrontation entailed at common law -- in place of the policy-oriented rule of Ohio v. Roberts, 448 U.S. 56 (1980) -- whether the out-of-court statement of the unavailable witness was reliable. In footnote 6, the Crawford opinion notes, "The one deviation [from the rule against out-of-court testimonial statements against the accused in a criminal case] that we have found involves dying declarations. The existence of that exception as a general rule of criminal hearsay law cannot be disputed."

Whether that historical exception is incorporated in the Confrontation Clause has not been squarely presented in a case before the high court to date. However, the Kansas Supreme Court has adopted it in the case of State v. Jones, No. 97,279. Kansas Supreme Court Blog has this summary. The full text is here.