Do changes in transcardiac impedance modulation correlate with haemodynamic status?

Implantable cardiac pacemakers and defibrillators have the ability to revert a variety of arrhythmias to normal sinus rhythm. For correct operation, such devices require accurate arrhythmia classification. Arrhythmia classification by these devices could be improved with the addition of a suitable haemodynamic sensor. This study investigated the use of transcardiac impedance for haemodynamic sensing. Ventricular fibrillation, ventricular tachycardia, electro-mechanical dissociation and five rates of ventricular pacing, each having a different associated level of haemodynamic compromise, were induced in each of seven mongrel dogs. The amplitude responses of the modulations of transcardiac impedance were compared with those of arterial pulse pressure (an established measure of haemodynamic status), and changes in cycle length. The correlation coefficient for changes in transcardiac impedance modulation amplitude and arterial pulse pressure was found to be 0.89. For transcardiac impedance modulation amplitude and cycle length, the correlation coefficient was 0.77, and for arterial pulse pressure and cycle length, the correlation coefficient was 0.85. In the acute anaesthetised dog, changes in the amplitude of transcardiac impedance modulations were shown to reflect different levels of haemodynamic status.