Complex repolarization dynamics in ex vivo human ventricles are independent of the restitution properties.

AIMS: The mechanisms of transition from regular rhythms to ventricular fibrillation (VF) are poorly understood. The concordant to discordant repolarization alternans pathway is extensively studied; however, despite its theoretical centrality, cannot guide ablation. We hypothesize that complex repolarization dynamics, i.e. oscillations in the repolarization phase of action potentials with periods over two of classic alternans, is a marker of electrically unstable substrate, and ablation of these areas has a stabilizing effect and may reduce the risk of VF. To prove the existence of higher-order periodicities in human hearts. METHODS AND RESULTS: We performed optical mapping of explanted human hearts obtained from recipients of heart transplantation at the time of surgery. Signals recorded from the right ventricle endocardial surface were processed to detect global and local repolarization dynamics during rapid pacing. A statistically significant global 1:4 peak was seen in three of six hearts. Local (pixel-wise) analysis revealed the spatially heterogeneous distribution of Periods 4, 6, and 8, with the regional presence of periods greater than two in all the hearts. There was no significant correlation between the underlying restitution properties and the period of each pixel. CONCLUSION: We present evidence of complex higher-order periodicities and the co-existence of such regions with stable non-chaotic areas in ex vivo human hearts. We infer that the oscillation of the calcium cycling machinery is the primary mechanism of higher-order dynamics. These higher-order regions may act as niduses of instability and may provide targets for substrate-based ablation of VF.

Proceedings of the AST heart allocation meeting at the American Transplant Congress, Philadelphia, Pennsylvania, May 4, 2015.

Ensuring fair and equitable allocation of donor hearts in the US is the charge of the Organ Procurement and Transplantation Network (OPTN). However, the recent increase of candidates waiting without a corresponding increase in available donors, higher waitlist mortality rates in higher status patients, the presence of disadvantaged subgroups, and the changing management of heart failure patients with increased VAD usage, has necessitated review of allocation policy. Therefore, the Heart Subcommittee of the OPTN/UNOS Thoracic Committee is exploring a further-tiered allocation system, devising a "straw man" model as a starting point for modeling analyses and public discussion. On May 4, 2015, an American Society of Transplantation (AST)-endorsed forum to discuss these potential proposed changes took place. Attendees included 41 people, mostly highly experienced transplant cardiologists and cardiothoracic surgeons, representing 19 heart transplant centers across the US, UNOS, and the Scientific Registry of Transplant Recipients (SRTR). There was unanimous agreement that the potential proposed policy will require careful wording to avoid ambiguity and "gaming" of the system, and strong support for abolishment of local organ sharing in favor of geographic sharing. However, contention existed concerning the appropriate prioritization levels of ECMO, temporary VAD/TAH patients as well as the 30-day LVAD listing.