Heart failure is when the heart can’t supply enough blood to meet the body’s demands. A variety of heart diseases like ischemia and valvular disease can impair the heart’s ability to pump out blood, and over time can lead to heart failure. This can happen in two ways, either the heart’s ventricles can’t pump blood hard enough during systole, called systolic heart failure, or not enough blood fills into the ventricles during diastole, called diastolic heart failure. In both cases, blood backs up, causing congestion or fluid buildup, which is why it’s also often called congestive heart failure.
All right, so the heart needs to squeeze out a certain volume of blood each minute, called cardiac output, which is the heart rate - or the number of beats in a minute - multiplied by the stroke volume – or the volume of blood squeezed out with each heartbeat. Then the ejection fraction is the portion of blood that’s pumped out of the left ventricle- in other words the stroke volume divided by the total left ventricular volume. The ejection fraction is normally around 50 to 70%, between 40 to 50% is borderline, and anything below 40% is systolic heart failure or heart failure with reduced ejection fraction.
There’s also diastolic heart failure, or heart failure with preserved ejection fraction. That’s where the heart has very thick ventricular walls so that the chamber doesn’t get an adequate load of blood, so the heart is squeezing hard enough but not filling up enough. In this case, the stroke volume is low, but the ejection fraction’s normal.
All right, so heart failure can affect the right ventricle, the left ventricle, or both ventricles, so biventricular heart failure, which defines where the failure is happening - and then there’s systolic or diastolic failure, which defines why the failure is happening. With left-ventricular or left-sided heart failure, blood gets backed up into the lungs, and that causes pulmonary hypertension and pulmonary edema. Because of differences in diffusion rates, all the extra fluid makes oxygenation harder, but ventilation of carbon dioxide still works pretty well. Patients often have dyspnea, as well as orthopnea or difficulty breathing when lying down flat. That’s because lying flat allows more venous blood to flow back to the heart and into the pulmonary circulation -worsening the congestion. All this extra fluid in the lungs causes crackles or rales on auscultation. A sign of severe left ventricular systolic failure is pulsus alternans, which is when there’s alternating strong and weak peripheral pulses. This occurs because the ejection fraction is significantly decreased, which in turn causes a reduction in stroke volume, so more blood will remain in the ventricle. As a result, during the next systole, the myocardial muscle will be stretched more than usual, leading to an increase in myocardial contraction and a stronger systolic pulse. Now with right-ventricular or right-sided heart failure, blood gets backed up in the body. That can cause jugular venous distention, which can be seen with the patient sitting at 45 degrees as the jugular vein having a fluid wave that represents the filling level. Normally it should be less than 3 centimetres vertical height above the sternal angle, but in heart failure it goes higher than that. Blood can also back up into the liver and the spleen, and both can get enlarged. Excess fluid can also move into the interstitial spaces near the surface of the liver and spleen, and collect in the peritoneum, causing ascites. Finally, fluid that backs up into the interstitial spaces within soft tissues in the legs causes pitting edema. That’s where applying pressure with a finger leaves a pit in the tissue for a few moments. This mostly affects the legs, because gravity causes most of the fluid to “pool” there. Now, since the ventricles work in series, left-sided heart failure can also cause right-sided heart failure, and more rarely, right-sided heart failure will cause left-sided heart failure as well, since the backing up of blood in the venous system will affect the arterial system over time. So patients often develop signs of both right and left-sided heart failure.
Now, if the ventricles are stiffened or dilated, eventually the atria will also undergo remodeling to adapt to the higher filling pressures. For this reason, in heart failure, there’s often a third heart sound or S3 heard on auscultation, which occurs after S1 and S2. Finally, in advanced heart failure, there’s decreased tissue perfusion leading to a resting sinus tachycardia, cool, pale, sometimes cyanotic extremities, and diaphoresis or excessive sweating due to hypotension, as well as narrow pulse pressure due to the drop in ventricular stroke volume.
On a chest X ray there might be changes like pulmonary edema or cardiomegaly, but there are no specific signs that point directly to heart failure. On an ECG, there might be clues about the underlying cause of heart failure like an arrhythmia or evidence of coronary artery disease.
In a patient with any type of congestive heart failure, the key lab value is the brain natriuretic peptide or BNP. A BNP level above 400 pg/ml is typical in heart failure, between 100 and 400 pg/ml is borderline, so further testing needs to be done, and below 100 pg/ml is unlikely to be heart failure. BNP levels can also be used to monitor a response to treatment as well.
Echocardiography is then done to confirm the diagnosis of heart failure. It can estimate the ejection fraction, as well as measure ventricular wall and chamber size which helps distinguish systolic versus diastolic heart failure. It can also assess the heart valves and estimate the pulmonary arterial pressure, to help identify causes and effects of the heart failure.