Heart failure is a condition in which the structure or function of the heart does not allow for sufficient cardiac output, or blood flow, to satisfy the body’s needs. It is different from cardiac arrest, a situation in which there is no cardiac output at all. When activity levels are normal and the blood flow is low, it is often referred to as congestive heart failure.

Classification of Heart Failure

There are many different ways to categorize heart failure, including:

• The side of the heart involved (left heart failure vs. right heart failure).
• Whether the abnormality is due to contraction or relaxation of the heart (systolic dysfunction vs. diastolic dysfunction).
• Whether the problem is primarily increased venous back pressure (behind) the heart or failure to supply adequate arterial perfusion (in front of) the heart (backward vs. forward failure).
• Whether the abnormality is due to low cardiac output with high systemic vascular resistance or high cardiac output with low vascular resistance (low-output heart failure vs. high-output heart failure).
• The degree of functional impairment conferred by the abnormality (as in the NYHA functional classification).

New York Heart Association (NYHA) Functional Classification

The NYHA Functional Classification provides a simple way of classifying the extent of heart failure. It places patients in one of four categories based on how much they are limited during physical activity; the limitations/symptoms are in regards to normal breathing and varying degrees in shortness of breath and or angina pain.

The classes (I-IV) are:

• Class I: No limitation is experienced in any activities; there are no symptoms from ordinary activities.
• Class II: Slight, mild limitation of activity; the patient is comfortable at rest or with mild exertion.
• Class III: Marked limitation of any activity; the patient is comfortable only at rest.
• Class IV: Any physical activity brings on discomfort and symptoms occur at rest.

This score documents the severity of symptoms, and can be used to assess response to treatment. While its use is widespread, the NYHA score is not very reproducible and doesn’t reliably predict the walking distance or exercise tolerance in formal testing.

American College of Cardiology (ACC) Classification System

In its 2001 guidelines, the American College of Cardiology (ACC) / American Heart Association (AHA) working group introduced four stages of heart failure:

• Stage A: Patients at high risk for developing heart failure in the future, but no functional or structural heart disorder.
• Stage B: Structural heart disorder, but no symptoms at any stage.
• Stage C: Previous or current symptoms of heart failure in the context of an underlying structural heart problem, but managed with medical treatment.
• Stage D: Advanced disease requiring hospital-based support, a heart transplant, or palliative care.

The ACC staging system is useful in that Stage A encompasses “pre-heart failure” – a stage where intervention with treatment can presumably prevent progression to overt symptoms. ACC Stage A does not have a corresponding NYHA class. ACC Stage B would correspond to NYHA Class I. ACC Stage C corresponds to NYHA Class II and III, while ACC Stage D overlaps with NYHA Class IV.

How Do Left Ventricular Assist Devices Help?

Patients with NYHA Class III or IV heart failure may benefit from a current treatment that involves the use of the Heartmate II, which is a left ventricular assist device (LVAD). LVADs are battery-operated mechanical pump-type devices that are surgically implanted on the upper part of the abdomen. They take blood from the left ventricle and pump it through the aorta. LVADs are becoming more common and are often used by patients who have to wait for heart transplants.

Related Articles:

• Left Ventricular Assist Devices
• Heartmate II LVAD Recall

The early VADs emulated the heart by using a “pulsatile” action where blood is alternately sucked into the pump from the left ventricle then forced out into the aorta. Devices of this kind include the HeartMate, which was approved for use in the U.S. by the FDA in October 1994. These devices are commonly referred to as first generation VADs.

More recent work has concentrated on continuous flow pumps, which can be roughly categorized as either centrifugal pumps or axial flow impeller driven pumps. These pumps have the advantage of greater simplicity resulting in smaller size and greater reliability. These devices are referred to as second generation VADs. A side effect is that users will not have a pulse or that the pulse intensity will be seriously reduced, and users will need to carry documentation saying that the lack of a pulse does not mean that they are dead.

Third generation VADs suspend the impeller in the pump using either hydrodynamic or electromagnetic suspension, thus removing the need for bearings and reducing the number of moving parts to one.

Another technology undergoing clinical trials is the use of transcutaneous induction to power and control the device rather than using percutaneous cables. Apart from the obvious cosmetic advantage, this reduces the risk of infection and the consequent need to take preventative action. A pulsatile pump using this technology has CE Mark approval (meets European guidelines) and is in clinical trials for U.S. FDA approval.

Left ventricular assist devices (LVADs) are battery-operated mechanical pump-type devices that are surgically implanted on the upper part of the abdomen. They take blood from the left ventricle and pump it through the aorta. LVADs are becoming more common and are often used by heart failure patients who have to wait for heart transplants.

How Do LVADs Function?

Most ventricular assist devices (VADs) operate on similar principles, including the Thoratec Heartmate II. A cannula, a tube that can be inserted into the body with the purpose of delivering or removing fluid, is inserted into the apex of the appropriate ventricle. Blood passes through the ventricle to a pump and then through a tube on the device to the aorta in the case of an LVAD, or to the pulmonary artery in the case of a right ventricular assist device (RVAD). The pump is powered through a lead that connects it to a controller and power supply. In some cases, there is also a tube to vent the pump to outside air.

The Jarvik 2000 operates slightly differently – the pump is actually located inside the left ventricle and its outflow passes through the apex of the ventricle to a tube that leads to the aorta.

Major distinguishing features between the different VADs are the pump (which can vary substantially in method of operation, size, and placement), the controller, the materials used both for the pump and the associated tubes and cannulas, and the lead between the pump and the controller/power supply.

Pulsatile Pumps vs. Continuous Flow Pumps

Pumps used in VADs can be divided into two main categories – pulsatile pumps, which mimic the natural pulsing action of the heart, and continuous flow pumps.

Pulsatile VADs use positive displacement pumps. In some of these pumps, the volume occupied by blood varies during the pumping cycle, and if the pump is contained inside the body then a vent tube to the outside air is required. The only three LVADS approved by the FDA for use in the U.S. are all pulsatile pumps. All were approved between 1994 and 1998, indicating the relative maturity of this technology.

Continuous flow VADs normally use either centrifugal pumps or axial flow pumps. Both types have a central rotor containing permanent magnets. Controlled electric currents running through coils contained in the pump housing apply forces to the magnets, which cause the rotors to rotate. In the centrifugal pumps, the rotors are shaped to accelerate the blood circumferentially and thus cause it to move towards the outer rim of the pump. Whereas in the axial flow pumps, the rotors are more or less cylindrical with blades that are mostly helical, causing the blood to be accelerated in the direction of the rotor’s axis.

An important issue with continuous flow pumps is the method used to suspend the rotor. Early versions used solid bearings; however, newer pumps, some of which are approved for use in the European Union, use either electromagnetic or hydrodynamic suspension. These pumps contain only one moving part. Manufacturers claim that these methods of suspension not only virtually eliminate wear, but also reduce damage to blood cells.