The American economy, slowed by last fall's 43-day government showdown, grew at a sluggish 0.5 per cent annual pace from October through December, the Commerce Department reported Thursday in downgrade of its previous estimate. US gross domestic — the nation's output of goods and services — decelerated in the fourth quarter after registering impressive growth of 4.4 per cent from July through September and 3.8 per cent from April through June. [...]