The utility of pacemaker evoked T wave amplitude for the noninvasive diagnosis of cardiac allograft rejection

Previous work suggested that pacemaker evoked T wave amplitude (ETWA) may b e a sensitive noninvasive marker of cardiac allograft rejection. A Topaz QT sensing rate responsive pacemaker (Vitatron Medical) was implanted at tran splantation using epicardial ventricular leads in 45 recipients (35 males; median age 51 years, range 20-63). The median duration of follow-up was 129 days (range 4-327). The ETWA at a paced rate of 100 beats/min was measured daily during hospitalization and at each outpatient attendance (900 readin gs). Endomyocardial biopsies were at routine intervals or when otherwise cl inically indicated (257 biopsies with concurrent ETWA data). There Ir ere 5 8 episodes of rejection greater than or equal to grade 3a in 28 patients. T he biopsies were classed as either no rejection (grade greater than or equa l to 3a) or rejection requiring treatment (grade greater than or equal to 3 a). The median normalized ETWA was 100.8% (range 24.6-239.7) without reject ion and 89.9% (17.0-189.7) with rejection (Mann-Whitney U Test: P = 0.028). The performance of ETWA monitoring as a diagnostic test for the individual recipient was evaluated with exponentially weighted moving average quality control charts. For the diagnosis of all rejection episodes, ETWA monitori ng had a sensitivity of 55%, a specificity of 62%, a positive predictive va lue of 30%, and negative predictive value of 83%. It is concluded that alth ough analysis of pooled data showed a significant reduction in normalized E TWA with biopsy proven rejection, ETWA monitoring requires further refineme nt to improve sensitivity before it can be considered a clinically useful t echnique for the non-invasive diagnosis of cardiac allograft rejection in i ndividual recipients.