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Department of Cardiothoracic and Respiratory Sciences, Second University of Naples, V. Monaldi Hospital, via L. Bianchi, Naples, 80131 Italy
(Email: aledellacorte{at}libero.it).
We read with interest the article by Kaiser and colleagues [1] on the long-term outcomes of valve replacement for infective endocarditis (IE) in intravenous drug users (IVDU) versus non-IVDU. We congratulate the authors for having focused on an increasingly important yet scarcely emphasized issue to date. Our previously published results in 39 IVDU and 85 age-matched non-IVDU [2] were similar to theirs; hospital and long-term survival did not significantly differ between the two patient groups. The patients in the two studies were comparable in terms of preoperative profile and IVDU received bioprostheses more often than non-IVDU in both experiences.
As in our study [2], Kaiser and colleagues [1] also observed significantly higher rates of reoperation for IE recurrence in IVDU compared with non-IVDU; of note, 88% of IVDU and 50% of non-IVDU who experienced recurrence had received a bioprosthesis [1]. We wondered whether the authors investigated the risk factors for recurrence; their sample size and event rates seemed adequate to perform a risk factor analysis, and indeed they performed it for late mortality. Our overall recurrence rate in IVDU was 19% (7 cases, corresponding to a linearized rate of 6% patients/year) [2]: although not reported in our previous article, among IVDU, 36% of those with bioprostheses had recurrence develop versus 10% of those with mechanical valves (p = 0.08), with the lack of statistical significance being likely due to the small numbers. Having focused in their comment on the question of prosthesis choice in IVDU [1], the authors were expected to attempt ruling out the respective roles of prosthetic type and drug use in IE recurrence.
Kaiser and colleagues [1] concluded suggesting that bioprosthetic valves could be an appropriate choice; nevertheless this statement seemed to be derived from their general preference for tissue valves (testified by the predominant implantation of biological substitutes also in the non-IVDU group) rather than from their study results. Actually the statement that young IVDU had similar survival as the older non-IVDU was not based on evidence; survival curves were really similar between the two groups only after adjusting for age [2], which points out that drug use per se may not significantly affect long-term survival after IE surgery. This may imply that IVDU receiving biological substitutes will live long enough to require a reoperation, if not for IE recurrence, almost surely for valve degeneration. The IVDU are predisposed to transient bacteremia more than non-IVDU, and a degenerating bioprosthesis is more prone to bacterial seeding. In patients with bioprostheses, endocarditis at first operation is a risk factor for emergency reoperation [3] with quadruplicated mortality compared with elective reoperation. Mortality rates as high as 30% were reported after reoperation for recurrent IE [4], and this should be weighted against the possibility of adverse events due to the poor compliance of IVDU to anticoagulation. More studies are required to assess, with a reliable level of evidence, which valve substitute performs better in this difficult setting.
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  S. P. Kaiser, S. J. Melby, and J. S. Lawton Reply Ann. Thorac. Surg., March 1, 2008; 85(3): 1142 - 1142. [Full Text] [PDF]
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