Anatomic landmarks for use when measuring intracardiac pressure with fluid-filled catheters

For determining the influence of hydrostatic pressure due to external trans ducer placement during intracardiac pressure measurements, we reviewed 200 magnetic resonance imaging and computer tomographic examinations of the che st in patients aged 23 to 95 years, and found that positions within the car diac chambers can be accurately estimated using external landmarks that ref erence fractions of the anteroposterior distance at the fourth intercostal space. This method of locating cardiac chambers is superior to methods that rely on fixed reference distances, and is applicable to men and women of a ll ages regardless of the presence of obesity, obstructive airways disease, left ventricular hypertrophy, or prior cardiothoracic surgery.