WP if class_exists

<li class="feature-<?php echo ++$i; ?> <?php if ( $i <= 1 ) echo 'activeSlide'; ?>">
<?php if (class_exists('activeSlide') { ?>
<a href="<?php echo get_post_meta($post->ID, 'custom_permalink', true); ?>"><?php the_title(); ?><?php if ( $i <= 1 ) echo '<img src="/parents/sandbox/wp-content/themes/sandbox/images/active-nav-arrow.png" />'; ?></a>
<?php } else { ?>
<a href="<?php echo get_post_meta($post->ID, 'custom_permalink', true); ?>"><?php the_title(); ?></a>
</li>