Monday, June 28, 2010

Why Did Dick Cheney Develop Heart Failure?

Years ago, when I was indoctrinated as a fellow in to American College of Cardiology, Dick Cheney - then a former secretary of state, was the keynote speaker at our commencement ceremony. His keynote speech reflected on what it was like to watch his father die following a massive heart attack, comforted only by morphine, oxygen, bed rest. By then, Mr. Cheney, already a recipient of two bypass operations, made a point to thank the cardiovascular community for helping him.

Many years later, Mr. Cheney's complicated yet remarkable cardiovascular history reads like a social studies timeline - one with heart attacks, arrhythmias, blood clots, and now, congestive heart failure. (Of course, political spin meisters want to make sure we call it "fluid retention" rather than congestive heart failure, since "failure" is not an option when speaking of all things political).

Congestive heart failure is nothing more than an insufficient pumping of blood to meet the body's needs. As a result, the kidneys detect the decreased perfusion pressure and trigger the release of a cascade of hormones to increase the blood pressure to maintain perfusion of the tissues. Some of the hormones help retain fluid in the vascular space. If this fluid becomes too excessive, the fluid can spill into the lung resulting in a sensation of shortness of breath, usually worse when lying flat. One of the main drugs used to fool the kidneys to release the accumulated fluid are diuretics - the most common being furosemide (Lasix).

There are a number of things that may have contributed to the development of Mr. Cheney's heart failure. Since HIPAA knows no bounds with disclosing Mr. Cheney's heart history, we can use this opportunity to tease apart a few possibilities.

First, dead meat don't beat.

It doesn't help that Mr. Cheney has had many heart attacks in the past. With the progressive loss of healthy muscle cells to to the heavy lifting of contraction, the ejection fraction falls. At first, the heart compensates by recruiting other, non-injured segments of heart muscle to take up the slack, but with each successive heart attack, the reserve heart muscle dwindles. Lose enough muscle and the heart must rely on increasing the rate at which if contracts to increase output, but for hearts already with limited blood flow this might lead to futher shortage of oxygen to the heart muscleto When this happens, the heart rate kicks up just a bit to increase cardiac output. If it kicks up too much, the heart can outstrip it's own oxygen supply, resulting in additional injury to the heart. This is part of the reason medication that slow the heart rate (beta blockers) can be helpful adjuncts to preserving heart muscle function and slowing the progression of worstened heart failure.

Second, Mr. Cheney's atrial fibrillation.

The loss of coordinated pumping of the top chambers (atria) just before the lower pumping chambers (ventricles) can lead to 10-20% drop in effective cardiac output in some patients. The irregularity of the heart's rhythm while in atrial fibrillation also causes a loss of coordinated closing of the normally one-way valves that direct the flow of blood through the heart, further compromising the heart's pumping ability. Rate control of atrial fibrillation or the restoration of normal sinus rhythm in the heart are often important adjuncts to the treatment of atrial fibrillation.

Third, is the presence of Mr. Cheney's defibrillator.

Although we do not know for sure, it would not be surprising if many of Mr. Cheney's heart beats are being supplied by his defibrillator's pacemaker feature. Excessive pacing the right ventricle can cause a dis coordinated beating of the lower pumping chambers, resulting in a subtle, but real, fall in cardiac function during paced heart beats compared to beats that are not paced and normally conducted from the top to bottom heart chambers. At some point in the future, Mr. Cheney might benefit, in appropriate circumstances, by adding extra pacing wire to his existing defibrillator system (so-called biventricular pacing) to re-coordinate the contraction process of his heart chambers above and beyond that which can be achieved with medications alone.

Finally, might he have new portions of heart muscle lacking sufficient oxygen?

Not all coronary arteries that might be partially blocked can be revascularized during surgeries or angioplasties. As a result, some segments of heart muscle might not have enough blood flow to maintain proper function, yet have just enough to survive intact. Many of our medications help lower blood pressure to decrease the work the heart has to perform on a beat-to-beat basis, dilate blood vessels to improve coronary blood flow, and work to decrease the negative affects that excessive adrenaline-like compounds can have on the heart's remaining muscle cells. The very fact that his doctors did not feel further invasive procedures were necessary suggests Mr. Cheney's revacularization options are limited at this point.

So given his current setback, what should we expect regarding his prognosis?

Hard to know. But given what I know about the successful management of heart failure these days, I wouldn't count him out quite yet.



Anonymous said...

Well, if they got him dry and he is not already on high dose oral diuretics, maybe 1 year.

If not, he will be back in hospital like 26 percent of all Americans, in 30 days.

Anonymous said...

Two weeks, maybe less, jeez