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Cardiovascular Research 2001 49(1):244-245; doi:10.1016/S0008-6363(00)00250-9
© 2001 by European Society of Cardiology
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Copyright © 2000, European Society of Cardiology

Comparison of mitral valve prolapse in dogs and humans

T.O. Cheng

Division of Cardiology, Department of Medicine The George Washington University, Medical Center, Washington, DC, USA

Received 10 October 2000; accepted 10 October 2000

To the Editor:

I read with great interest the comprehensive review on mitral valve prolapse in the dog by Pedersen and Häggström [1]. Although I have had a longstanding interest in mitral valve prolapse in humans and knew that mitral valve prolapse is the commonest cardiac disease in the dog [2] as in humans [3], I have never examined a dog with mitral valve prolapse. However, I was greatly impressed by the similarities between mitral valve prolapse in the dog and in the human, as were convincingly presented by Pedersen and Häggström [1].

Sudden cardiac death is a recognized, though relatively rare (only 106 cases reported up to 1989 [4]), complication of mitral valve prolapse in humans [5]. It was interesting to speculate on the mechanism of sudden cardiac death in mitral valve prolapse. Pedersen and Häggström cited the work of Falk and Jönsson [6] who found nonatherogenic dysplasia of the intramural coronary arteries in dogs that died suddenly. Although similar finding was reported in humans with mitral valve prolapse [7,8], its significance in contributing to sudden cardiac death is unclear. Evidence to date suggests that the predominant mechanism of sudden cardiac death in mitral valve prolapse is fatal ventricular arrhythmias [9]. Therefore, it would be extremely difficult for a pathological study to prove or disprove conclusively the causal relation between mitral valve prolapse and sudden cardiac death which is a physiological event [10].

A recent report from the Mayo Clinic [11] seemed to indicate that the incidence of sudden cardiac death in mitral valve prolapse has been underestimated and that sudden cardiac death occurred only in patients with mitral valve prolapse and significant mitral regurgitation. This author and other investigators from the literature [12] have encountered patients with mitral valve prolapse who died suddenly even though the degree of their mitral regurgitation was mild. The mode of sudden cardiac death in mitral valve prolapse is presumably ventricular tachyarrhythmias deteriorating into ventricular fibrillation.

The mechanism of ventricular tachyarrhythmias in mitral valve prolapse is multifactorial [4]:

1. abnormal tension on the papillary muscle and adjacent myocardium from the prolapsing mitral leaflet(s);
2. endocardial friction lesions produced by contact between the tense chordae tendineae attached to the prolapsing mitral leaflet(s) and left ventricular endocardium;
3. diastolic dumping of the floppy mitral leaflets;
4. coronary embolism from deposits of fibrin and platelets on the fissures of the redundant leaflets and in the angle between the prolapsing posterior leaflet and the left atrial wall;
5. coronary vasospasm;
6. associated cardiomyopathy;
7. adrenergic hyperactivity [13,14];
8. increased QT dispersion [15,16];
9. hypomagnesemia [17].
Most of the aforementioned mechanisms suggest that it is the mitral valve prolapse per se rather than the severity of associated mitral regurgitation that is responsible for the occurrence of sudden cardiac death in mitral valve prolapse. This argument receives further support from long-standing observations that ventricular ectopy is not a feature of mitral regurgitation in rheumatic heart disease, irrespective of its severity, in which mitral leaflets are not voluminous [18]. I would be interested to hear comments from Pedersen and Häggström [1].


   References
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 References
 

  1. Pedersen H.D., Häggström J. Mitral valve prolapse in the dog: a model of mitral valve prolapse in man. Cardiovasc. Res. (2000) 47:234–243.[Free Full Text]
  2. Cheng T.O. Mitral valve prolapse. An overview. J. Cardiol. (1989) 19(Suppl. 21):3–20.
  3. Cheng T.O., Barlow J.B. Mitral leaflet billowing and prolapse. Its prevalence around the world. Angiology (1989) 40:77–87.[Web of Science][Medline]
  4. Cheng T.O. Mitral valve prolapse. Annu. Rev. Med. (1989) 40:201–211.[CrossRef][Web of Science][Medline]
  5. Cheng T.O. Mitral valve prolapse. Dis. Month (1987) 33:481–534.
  6. Falk T., Jönsson L. Ischaemic heart disease in the dog: a review of 65 cases. J. Small Anim. Pract. (2000) 41:97–103.[Web of Science][Medline]
  7. Morales A.R., Romanelli R., Boucek R.J., Tate L.G., Alvarez R.T., Davis J.T. Myxoid heart disease: an assessment of extravalvular cardiac pathology in severe mitral valve prolapse. Hum. Pathol. (1992) 23:129–137.[CrossRef][Web of Science][Medline]
  8. Burke A.P., Farb A., Tang A., Smialek J., Virmani R. Fibromuscular dysplasia of small coronary arteries and fibrosis in the basilar ventricular septum in mitral valve prolapse. Am. Heart J. (1997) 134:282–291.[CrossRef][Web of Science][Medline]
  9. Barlow J.B., Cheng T.O. The International Textbook of Cardiology. Cheng T.O., ed. (1987) New York: Pergamon Press. 497–524.
  10. Cheng TO. Sudden cardiac death in mitral valve prolapse. Circulation, in press.
  11. Grigioni F., Enriguez-Sarano N., Ling L.H., Bailey K.R., Seward J.B., Tajik A.J., Frye R.L. Sudden death in mitral regurgitation due to flail leaflet. J. Am. Coll. Cardiol. (1999) 34:2078–2085.[Abstract/Free Full Text]
  12. Pocock W.A., Barlow J.B., Marcus R.H., Barlow C.W. Mitral valvuloplasty for life-threatening ventricular arrhythmias in mitral valve prolapse. Am. Heart J. (1991) 121:199–202.[CrossRef][Web of Science][Medline]
  13. Boudoulas H., Reynolds J.C., Mazzaferri E., Wooley C.F. Metabolic studies in mitral valve prolapse syndrome: a neuro-endocrine-cardiovascular process. Circulation (1980) 61:1200–1205.[Abstract/Free Full Text]
  14. Dauber L.G. Death in opera: a case study, "Tales of Hoffman" – Antonia. Am. J. Cardiol. (1992) 70:838–840.[CrossRef][Web of Science][Medline]
  15. Cheng T.O. Increased dispersion of refractoriness in the absence of QT prolongation in patients with mitral valve prolapse and ventricular arrhythmias. Br. Heart J. (1995) 74:96.[Free Full Text]
  16. Cheng T.O. QT dispersion in mitral valve prolapse. Int. J. Cardiol. (1998) 64:219.[CrossRef][Web of Science][Medline]
  17. Cheng T.O. Mitral valve prolapse and hypomagnesemia. How are they causally related? Am. J. Cardiol. (1997) 80:976.[Medline]
  18. Barlow J.B., Kinsley R.H. Mitral regurgitation due to flail leaflet. N. Engl. J. Med. (1997) 336:1322.[Free Full Text]

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