private void WatchTopItemChanged(ListView listView, Action callOnChanged) {
  var lastTopItem = listView.TopItem;
  listView.DrawItem += delegate {
    if (lastTopItem != listView.TopItem) {
      lastTopItem = listView.TopItem;
      callOnChanged();
    }
  };
}

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

class MyListView : ListView {
    public event EventHandler TopItemChanged;

    protected virtual void OnTopItemChanged(EventArgs e) {
        var handler = TopItemChanged;
        if (handler != null) handler(this, e);
    }

    protected override void WndProc(ref Message m) {
        // Trap LVN_ENDSCROLL, delivered with a WM_REFLECT + WM_NOTIFY message
        if (m.Msg == 0x204e) {
            var notify = (NMHDR)Marshal.PtrToStructure(m.LParam, typeof(NMHDR));
            if (notify.code == -181 && !this.TopItem.Equals(lastTopItem)) {
                OnTopItemChanged(EventArgs.Empty);
                lastTopItem = this.TopItem;
            }
        }
        base.WndProc(ref m);
    }

    private ListViewItem lastTopItem = null;
    private struct NMHDR {
        public IntPtr hwndFrom;
        public IntPtr idFrom;
        public int code;
    }
}