How It Works: Science and Technology - Vol. 8

By Wendy Horobin | Go to book overview

Heart Surgery

Heart surgery, also called cardiovascular surgery, encompasses surgical techniques that correct or alleviate congenital heart defects and acquired conditions such as coronary heart disease and that mend wounds caused by the penetration of the heart by bullets, knife blades, or other objects.

The scope for treatment of complaints by cardiovascular surgery increased vastly with the introduction and development of open-heart surgery in the early 1950s. More recent advances, including minimally invasive surgery, have improved success rates and reduced recovery times.


Stopping the heart

For many cardiovascular procedures, the heart must be temporarily stopped so that its rhythmic contractions do not impede the surgeon's work. The connections between the heart and the circulatory system must also be clamped to prevent massive blood loss through the surgical opening. When these measures are taken, the body's supply of oxygenated blood from the lungs is disrupted—an occurrence that would normally cause the degeneration of the brain and other organs and would eventually kill the patient.

In most cases, the patient is kept alive by cardiopulmonary bypass, whereby blood that arrives at the heart through the inferior and superior venae cavae is diverted to a heart-lung machine. Such devices have oxygenators that imbue blood with oxygen and remove carbon dioxide before pumps inject the blood through catheters that feed into the patient's aorta. The blood then follows its usual path through the body.

In the first stage of a cardiopulmonary bypass, tubes called catheters are inserted into the appropriate veins and arteries to make the connections with the heart-lung machine. The machine is primed with a sufficient volume of donor blood to fill its working parts. The pumps are then switched on so that the heart-lung machine works in parallel with the patient's heart.

Once the heart-lung machine is working satisfactorily, the surgeon seals the entrances and exits of the heart with clamps and injects the heart muscles with a solution of potassium salts, which halts their contractions. Temporarily isolated and paralyzed, the heart is in a suitable condition for surgery to commence. At the end of surgery on the heart, the clamps are removed and blood flows into the heart. As soon as the paralysis owing to the potassium salts ends, the heart-lung machine is disconnected and the catheters withdrawn before the patient is stitched up.

This picture shows a
surgical procedure to
replace a defective heart
valve with an artificial
substitute. A surgeon
first threads loose sutures
between the polyester rim
of the artificial valve and
the edge of the opening
where the valve will be
positioned. Tightening the
sutures by pulling on the
ends of the thread then
draws the valve into place.


Hypothermic techniques

Before the invention of the heart-lung machine in 1953, hypothermia was the only means of sustaining life while the heart was temporarily stopped for surgery. Hypothermia—abnormally low body temperature—reduces the rate of the metabolic processes that drain oxygen from blood. In this way, the body's demand for oxygen would be diminished to such an extent that the oxygen content of static blood would be sufficient to maintain basic organ functions while the heart was stopped for up to five minutes of surgery.

The limited stoppage times allowed by early hypothermic techniques imposed severe restrictions on the amount of surgery that could be done without running an unacceptable risk of brain or other organ damage or even death. For this reason, hypothermic techniques fell into disuse soon after the invention of the heart-lung machine.

The use of heart-lung machines is not entirely free of problems, however. Blood that has been in contact with the metal, glass, and plastic inner surfaces of heart-lung machines can form clots and cause inflammation when it returns to a patient's body. These effects put the patient at risk of side effects and prolong recovery times. For these reasons, a group of surgeons from the Novosibirsk Institute of Circulatory Pathology, Russia, generated worldwide interest when they announced their success in using refined hypothermic techniques to allow heart stoppages for up to 90 minutes of open-heart surgery.

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How It Works: Science and Technology - Vol. 8
Table of contents

Table of contents

  • Title Page *
  • Contents *
  • Gold 1013
  • Governor 1017
  • Grass-Cutting Equipment 1018
  • Gravity 1020
  • Gun 1023
  • Gyrocompass 1028
  • Gyroscope 1030
  • Hair Treatment 1032
  • Halogen 1034
  • Hang Glider 1037
  • Head-Up Display 1039
  • Hearing 1041
  • Heart 1045
  • Heart Pacemaker 1048
  • Heart Surgery 1049
  • Heat Engine 1053
  • Heat Exchanger 1054
  • Heating and Ventilation Systems 1056
  • Heat Pump 1063
  • Helicopter 1065
  • Hi-Fi Systems 1071
  • High-Speed Photography 1077
  • Holography 1080
  • Hormone 1084
  • Horticulture 1088
  • Hosiery and Knitwear Manufacture 1090
  • Hurricane and Tornado 1094
  • Hydraulics 1100
  • Hydrocarbon 1105
  • Hydrodynamics 1109
  • Hydroelectric Power 1112
  • Hydrofoil 1116
  • Hydrogen 1118
  • Hydroponics 1120
  • Hygrometer 1123
  • Ignition System, Automobile 1124
  • Image Intensifier 1128
  • Immunology 1132
  • Induction 1138
  • Inertia 1142
  • Information Technology 1147
  • Ink 1151
  • Index i
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