Background Mechanical prosthetic heart valves are known for their durability; however, a malfunctioning prosthesis can deteriorate rapidly to become a life-threatening complication. Our aim was to calculate a numerical index to express the rate of clinical deterioration of patients presenting with a mechanical prosthetic heart valve thrombosis (PVT), called the index of deterioration (ID), and to evaluate its usefulness in predicting hospital outcomes. Results The median ID and range were (0.43, 0.03-3) NYHA class/day. A higher ID was significantly related to early development of PVT after native valve replacement, younger age, female gender, pregnancy, non-compliance to oral anticoagulation (OAC), low LVEF%, high mean pressure gradient across a mitral prosthesis, raised serum creatinine, and SGOT on admission (P < 0.05). Independent predictors were early presentation after native valve replacement, female gender, and non-compliance to OAC (P < 0.05). ID correlated positively with the need for urgent/emergency surgery, and the durations of cardiopulmonary bypass, postoperative mechanical ventilation, and positive inotropes. ID correlated negatively with the postoperative LVEF% (P < 0.05). Median ID of the 21 mortalities (0.75, 0.1-3) was > 2.1 times that of survivors (0.35: 0.03−2; P = 0.002), and the median ID of the 29 cases with postoperative complications (0.5, 0.1-1.5) was 2.5 times that of the 39 uneventful cases (0.2, 0.03-2; P = 0.011). The ID significantly predicted both mortality (odds ratio 3.87; 1.33-1.29; P = 0.013) and mortality and hospital complications (odds ratio 4.77; 1.49-15.2; P = 0.008). The respective discriminating abilities were AUC 0.734 (0.616-0.852; P = 0.002) and 0.724 (0.61-0.835; P < 0.001). EuroScore II correlated positively with ID (r = 0.571; P < 0.001) but showed better discriminative abilities. Conclusion The simple index of deterioration was useful in monitoring deterioration and predicting hospital progression and outcomes in patients presenting with PVT.

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