The Good News About Bad News

Each year 50 million Americans find themselves fighting what has become known as the “silent killer.”  High blood pressure (or hypertension) impacts over 16% of our population and leads to health problems ranging from heart failure to blindness and even kidney disease.  It would be easy to believe little good would ever come from such a health problem.  And indeed, for those patients with high blood pressure needing a hip or knee replacement, it may appear as a compounding problem.  Yet there is in fact some good news about the bad news of high blood pressure.  The chances of certain complications during knee or hip procedures are actually lower for patients with high blood pressure than for similar patients who do not suffer from such a comorbidity.

High blood pressure earned its name as the “silent killer” because in many cases the symptoms are not noticeable and remain undiagnosed until serious problems arise.  Because of this, a large number of patients diagnosed with high blood pressure can already have numerous complicating health issues by the time of the actual diagnosis.  It can then be reasoned that such patients would expect more  complications when going under the knife for a total hip replacement or a total knee replacement than patients without hypertension.

The biggest fear that comes to many minds would be heart failure or a heart attack during or resulting from the procedure.  However, there is good news to report.  Using the PearlDiver database containing over 104 million patient records, a sample of patients primarily under the age of 65 was compiled for both procedures and is displayed below in Table 1.

Table 1: Heart Attack/Heart Failure Resulting From Procedure

From 2004–2006, 14,880 distinct patients underwent total hip replacement.  Of these, 3,724 patients had previously been diagnosed with high blood pressure and still elected to have a total hip replacement.  Out of those patients diagnosed with high blood pressure, only 24 suffered heart failure or a heart attack as a result of the procedure. In comparison, 102 patients who were not diagnosed with the comorbidity suffered heart failure or a heart attack as a result of the procedure.  Clearly, although the number of patients with high blood pressure who underwent the procedure was far fewer than the number of patients without, a significantly lower percentage of patients with high blood pressure experienced heart failure or a heart attack resulting from the procedure. 

The same holds true for patients undergoing total knee replacements.  Of 27,891 distinct patients, only 62 with previously diagnosed high blood pressure experienced heart failure or a heart attack as a result of the procedure, in comparison to 223 distinct patients without high blood pressure who underwent total knee replacement.  These results are very counter-intuitive to what is commonly expected from such a diagnosis.  To answer the question of why this phenomenon is occurring, a more in-depth look is required. 

Among those patients suffering from a heart attack or heart failure, the age distribution follows a pattern of normal expectations.  The number of heart complications begins to rise in patients 45 or older.  As the age of these patients increases, so too does the number of incidents of heart attack or heart failure.  Thus with respect to age, patients within the subset follow a normal age distribution for such a complication, so it can be determined that age does not play a major role.

What else then could be the cause of this good news for patients with high blood pressure?  Are there other comorbidities having a greater impact on patients?  Diving more deeply into the PearlDiver data to find the root of this phenomenon, two other comorbidities were taken into account among these patients suffering from a heart attack or heart failure during surgery—obesity and diabetes.

A study completed by Duke University Medical Center released on June 1, 2005 (Diabetes, Hypertension And Obesity Negatively Effect Joint Replacement Outcomes, ScienceDaily, http://www.sciencedaily.com­ /releases/2005/06/050620005045.htm), concluded that surgical patients diagnosed with hypertension, obesity, or diabetes were more likely to suffer from post-operative complications. Furthermore, among the three diagnoses, obesity posed the greatest risk.  Because of these findings, the comorbidity with the greatest potential for an explanation was obesity.  The reasoning for this is if the comorbidity poses the greatest post-operative risk, it may be potentially risk-bearing during the operation as well.

To analyze the effects of obesity, the subset of patients within the PearlDiver database who experienced a heart attack or heart failure during either a total hip replacement or a total knee replacement were cross referenced with those who had been diagnosed with obesity prior to the procedure. 

The results of this analysis, shown in Table 2, reveal mixed results.  No patients diagnosed with high blood pressure and obesity suffered from a heart attack or heart failure while undergoing a total hip replacement, but 12 patients with the same diagnoses undergoing a total knee replacement were not as fortunate.  Patients without a diagnosis of high blood pressure fared differently with respect to total hip replacements, where 13 still suffered from a heart attack or heart failure, and 22 patients suffered the same complications while undergoing a total knee replacement.  So while there are some variations in the results of patients diagnosed with obesity, these numbers are still below the national obesity rate of 34% of adults over the age 20, according to the Centers for Disease Control.  With these considerations, this comorbidity cannot fully explain what is occurring to create more heart attacks and heart failures during procedures on patients without high blood pressure. 

Table 2: Hypertension/Obesity Comparison of Patients Suffering Heart Attack/Heart Failure During Procedure

Moving forward to examine diabetes, the same method of analysis was used within the PearlDiver database to measure its effects on patients undergoing total hip or knee replacements.  The numbers shown in Table 3 bear a stark difference to the results of the obesity analysis.

Table 3: Hypertension/Diabetes Comparison of Patients Suffering Heart Attack/HeartFailure During Procedure

These results show a very strong relation between the number of heart attacks or heart failures and diabetes.  Those patients diagnosed with diabetes along with high blood pressure fare much worse than those without diabetes, and of all patients diagnosed with high blood pressure that had a heart attack or heart failure during the procedure, over 88% had also been diagnosed with diabetes.  Of the 325 patients who had never been diagnosed with high blood pressure but still had a heart attack, almost 30% had been diagnosed with diabetes.  In total, of 411 patients in the PearlDiver database who suffered a heart attack or heart failure while having a total hip replacement or a total knee replacement, over 41% were diabetic!

This information leads to three very important conclusions.  First, while patients diagnosed solely with high blood pressure are less likely to have a heart attack when undergoing a total hip or knee replacement, this is not caused by random luck.  It isn’t a phenomenon at all.  The truth behind the circumstances is that another comorbidity is causing more heart attacks and heart failures than is high blood pressure.  This leads to the second conclusion.  While obesity may be the most threatening post-surgical comorbidity, for patients undergoing a total hip or knee replacement, diabetes poses the greatest threat during the procedure itself.  This condition, coupled with high blood pressure, can make things especially risky.