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  1. In the absence of heart failure:
    • CMVI may have a benign course for quite some time in many dogs.
      • The preclinical stage may last for 4-6 years, that is, a murmur of MR can be detected for 4-6 years prior to the onset of clinical signs of congestive heart failure.
      • In a recent large retrospective study of 558 dogs with CMVI, more than 60% of the preclinical (asymptomatic) dogs were still alive 70 months (> 5 years) after the initial diagnosis, and 69% of all the dogs survived or died from causes unrelated to CMVI during the follow-up period which averaged 2 years (Borgarelli et al. JVIM 2008;22:120-128).
    • In a clinical trial of Cavalier King Charles Spaniels with preclinical CMVI (all at various stages), the average time to CHF after enrolment was 3 years (Kvart et al. JVIM 2002;16:80-88).
      • The intensity of the heart murmur was related to the size of the heart and inversely related to the time to onset of heart failure.
      • The louder the heart murmur and the larger the heart, the sooner heart failure will develop.
    • Other factors that appear to be related to prognosis in the asymptomatic phase include breed, age, family history, presence of mitral valve prolapse, and indices of heart size including vertebral heart score (VHS) and left atrium:aorta (LA:Ao) ratio on echocardiography.
    • Sudden death has been reported infrequently in preclinical CMVI dogs (5/302 preclinical dogs = 1.6% in Borgarelli’s study above)
    • Large breed dogs as compared with small breed dogs with CMVI tend to:
      • Have a greater degree of depressed contractility
      • Have less mitral valve insufficiency
      • Have less thickening and prolapse of the mitral leaflets
      • Have lower intensity heart murmurs
      • Be more likely to manifest atrial fibrillation
      • Be of the same age
      • Have the same survival
  2. If congestive heart failure is present:
    • Symptoms can be controlled and exercise tolerance increased but animals usually succumb to this disorder within 2-3 years. Some dogs experience repeated bouts of acute heart failure. This may occur due to the development of an arrhythmia, excessive exercise, excessive sodium load, or rupture of a chordae tendinae. Frequently, these bouts of acute pulmonary edema can be stabilized, and these patients returned to the previous level of activity.
    • In Borgarelli’s retrospective study of 558 dogs with CMVI cited above, the median time to cardiac-related death was 33 months in dogs with mild to moderate heart failure and 9 months in dogs with advanced heart failure.
    • Factors related to poorer prognosis in the above study included increased age, presence of syncope, presence of arrhythmias, increased heart rate, increasing left ventricular size, presence of ascites, plasma urea concentration and the strongest predictor of all, increasing left atrial size.
  3. If pulmonary hypertension develops:
    • There are no good studies assessing the effect of pulmonary artery hypertension independent of other factors.
      • One study suggests it has no effect on survival.
  4. If ruptured chordae develops:
    • With therapy for acute fulminate pulmonary edema, many patients can be returned to compensation within 5 days. Their outcome can still be good with survival for another year or more.
    • In a retrospective study of 57 dogs with chordal rupture, the median survival time was 425 days after diagnosis, with 58% surviving > 1 year (for the dogs in whom follow-up was available) (Serres et al. JVIM 2007;21:258-264). This suggests that chordal rupture may not be as devastating a consequence of CMVI as previously speculated.