At a recent meeting of the British Cardiac Society concern was expressed at the risks of piercing the aorta during attempted transseptal catheterization of the left atrium. We wish to describe a needle designed to overcome this risk, which we have used at the Postgraduate Medical School of London for the past three years.Catheterization ofthe left side ofthe heart from the venous route by means of needle puncture of the interatrial septum was introduced in 1959 (Ross, 1959;Cope, 1959). The needle that was designed for this purpose had a wide bore (17 gauge) and allowed the passage of PE 50 polythene tubing through the needle and on into the left atrium and ventricle. The technique was improved by Brockenbrough and Braunwald (1960) who designed a needle that allowed larger catheters to be introduced into the left side of the heart over the needle. The advantages of this system were that the catheter and needle could be introduced by the percutaneous route via the femoral vein, the larger catheter allowed more accurate recordings of pressures, and selective angiocardiography could be carried out through it. Since this needle was employed the technique has come into widespread use as a method of major importance (Braunwald et al., 1962;Miller and Medd, 1964).However, transseptal catheterization has been associated with complications caused generally by inadvertent puncture either of the free wall of the atrium or of the aorta which is closely related to the anterior part of the interatrial septum. These complications have, in most cases, occurred in the hands of occasional or inexperienced operators but have also been more frequent since the Brockenbrough needle and catheter replaced the original
Combined hypothermia and extracorporeal circulation have become recognized as being complementary to one another; this is in contrast to the earlier pessimism that &dquo;it would combine the risks of two dangerous procedures.&dquo; Moderate hypothermia in the range of 29 to 30° C reduces the oxygen consumption by 50 to 60 per cent and so permits a low flow rate, with all its advantages, without risks of hypoxia. In the experimental animal, oxygen consumption drops to 15 per cent of the normal at 20° C. It has been deduced that between 10 to 12° C body temperature oxygen consumption becomes negligible', hence at this temperature total circulatory arrest should be possible without risks of ischemic changes for a much longer period than obtained at 30° C.The purpose of this work has been, firstly, to study oxygen consumption and blood gases at low body temperatures (9 to 10° C) and, secondly, to evaluate the biochemical, cardiac and circulatory changes which attend total cardiopulmonary bypass and deep hypothermia. MATERIAL AND METHODSFifteen unselected adult mongrel dogs 10 to 23 kg in weight were anaesthetized with Thiopentone, intubated and ventilated with room air using an intermittent positive pressure mechanical respirator. Both femoral arteries were cannulated, the right being used for monitoring arterial pressure and the left for perfusion. After a standard right thoracotomy, the superior and inferior venae cavae were cannulated and total cardiopulmonary bypass was established at 70 cc/kg of body weight using a disk oxygenator with a heat exchange unit2 through which ice water was circulated at a temperature of 3 to 5° C. The animals were thus cooled rapidly to 10 to 15° C and subsequently rewarmed.The animals were divided into two groups. Group 1. Ten animals were studied for electrolyte and other biochemical changes; in 5 the * From the Cardio-Thoracic Unit, Etherington Hall, Queen's University, Kingston, Ontario, Canada. oxygenating gas was pure oxygen and in the remainder a mixture of 95 per cent oxygen and 5 per cent carbon dioxide was used. During cooling and rewarming, heart rate and blood pressures, and esophageal, pericardial and rectal temperatures were recorded at 5-minute intervals.Arterial blood samples were obtained from the animal prior to perfusion, 5 minutes after the onset of total perfusion, at the lowest temperature reached, on rewarming to normal body temperature and lastly, 1 hour after the end of perfusion. The above samples were subjected to pH, C02 and PC02 per cent of saturation and electrolyte (sodium, potassium, magnesium, calcium and chloride) determinations.Group 2. Five animals were studied particularly for oxygen consumption. The esophageal temperature was lowered to 9 to 12° C. After the lowest temperature was reached, total circulatory arrest for varying periods of time was obtained by stopping the pump oxygenator. Heart rate and rhythm, blood pressure and esophageal, pericardial and rectal temperatures were recorded at 5-minute intervals. Arterial and venous samples were...
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