Via Jacques-Alain Miller, Zizek describes Lacan's notion of the sinthome as his late replacement for the concept of the symptom. The sinthome describes a network of points of contact with the Real, rather than a privileged and crucial point which analysis tries to dissolve. As Zizek describes, the sinthome underpins the cosmology-that-is-not-a-cosmology that Lacan lays out in Seminar XX:
"[Lacan's Seminar XX describes a] universe of radical split (between signifier and signified; between jouissance of drives and jouissance of the Other; between masculine and feminine) in which no a priori Law guarantees the connection or overlapping between the two sides, so that only partial and contingent knots--symptoms (quilting points, points of gravitation) can generate a limited and fragile co-ordination between the two domains. In this perspective, the 'dissolution of a symptom', far from bringing about the non-pathological state of full desiring capacity, leads, rather, to a total psychotic catastrophe, to the dissolution of the subject's entire universe. There is no 'big Other' to guarantee the consistency of the symbolic space within which we dwell: there are only contingent, local and fragile points of stability. . . .
The difference between these two notions of the symptom--the particular and the universalized ('sinthome')--accounts for the two opposed readings of the last shot of Hitchcock's Vertigo. . . . If we use the term 'symptom' in its traditional sense . . . , then the final shot does imply a happy ending: Scottie's obsession with Madeleine was his 'symptom', a sign of his ethical weakness, so that when he gets rid of her, his rectitude is restored. If we use the term 'symptom' in its more radical sense, however--if Judy/Madeleine is his sinthome--then the final shot implies a catastrophic ending: when Scottie is deprived of his sinthome, his entire universe falls apart, loses its minimal consistency." (116-7)
It seems to me that this notion of the sinthome draws Lacan closer to Deleuze's philosophy of connections, planes of immanence, and intensities and farther away from his own insistence on radical disconnects. In this way, while Lacan is doffing his hat to Aristotle in Seminar XX, it could be conceived as a gesture of fond farewell. Goodbye to a cosmology based on the primum mobile of inscrutable Otherness, and hello to a universe of networked and serialized objects that set us adrift.