6.   Goodwill and Intangible Assets. The change in the carrying amount of goodwill for the six-month period ended June 30, 2024 is detailed as follows (in thousands):

​

​

Total accumulated goodwill impairment losses aggregated to $8.3 million as of June 30, 2024 and December 31, 2023, respectively. We did not have any goodwill impairments for the six-month periods ended June 30, 2024 or 2023. The total goodwill balances as of June 30, 2024 and December 31, 2023 were related to our cardiovascular segment.

​

Other intangible assets at June 30, 2024 and December 31, 2023 consisted of the following (in thousands):

​

​

​

Aggregate amortization expense for the three and six-month periods ended June 30, 2024 was $14.8 million and $29.4 million, respectively. Aggregate amortization expense for the three and six-month periods ended June 30, 2023 was $13.4 million and $25.7 million, respectively.

​

We evaluate long-lived assets, including amortizing intangible assets, for impairment whenever events or changes in circumstances indicate that their carrying amounts may not be recoverable. We perform the impairment analysis at the asset group for which the lowest level of identifiable cash flows is largely independent of the cash flows of other assets and liabilities. We determine the fair value of our amortizing assets based on estimated future cash flows discounted back to their present value using a discount rate that reflects the risk profiles of the underlying activities. We did not identify indicators of impairment for our intangible assets based on our consideration of triggering events for the six-month periods ended June 30, 2024 and 2023, respectively.

​

Estimated amortization expense for developed technology and other intangible assets for the next five years consisted of the following as of June 30, 2024 (in thousands):

​