Usefulness of right ventricular pulse pressure as a potential sensor for hemodynamically unstable ventricular tachycardia

Arrhythmia recognition strategies and hardware decisions for the implantable cardioverter-defibrillator--a review

The avoidance of inappropriate shocks from the implantable cardioverter-defibrillator (ICD), together with its need to apply antitachycardia pacing to either atria or ventricles, demands considerable sophistication in the design of algorithms to interpret electrical or other cardiac signals in real-time. Methods based on rate and using single short-gap bipolar leads lack discrimination. Right ventricular electrogram morphology algorithms offer improvement but no universal algorithm exists; however, for any given patient an optimum algorithm of this type might be found. One improvement would be to provide atrial information in addition, by employing more than one electrode or a long-gap single bipolar lead. Alternatively, transducer signals could be included, once their efficacy and reliability have been improved. A different approach would be to use the much more sophisticated algorithms at present being tried with surface electrocardiograms. Integrated Circuit technology is reaching the point where this could be done but the requirement for exceptionally high reliability means that special system structures, such as a Memory Intensive Computer Architecture, may be required. When decisions on these approaches are to be made, it must also be remembered that ICDs will soon be implanted and programmed as a routine rather than a highly specialized procedure.

The range of sensors and algorithms used in rate adaptive cardiac pacing

Implantable sensors play an important role in physiological cardiac pacing. Sensors can be classified according to the technical methods in which sensing is achieved: the sensing of the evoked ventricular response, intrathoracic impedance and body acceleration forces, and the incorporation of special sensors on pacing electrodes. These sensors differ in their relative merits in terms of speed, proportionality, sensitivity, and specificity of rate response. The efficacy of a sensor can be significantly modified by the algorithm used in relating sensor signal to a pacing rate change. The currently available types of sensors and algorithms are summarized and compared in this review article. The relative merits of these sensors and algorithms form the basis for designing a multisensor pacing system.

Short-term reproducibility over time of right ventricular pulse pressure as a potential hemodynamic sensor for ventricular tachyarrhythmias

The implantable cardioverter defibrillator (ICD) has been shown to effectively terminate episodes of ventricular tachyarrhythmias. Multiple investigators have suggested that the incorporation of hemodynamic sensors may allow ICDs to differentiate between hemodynamically unstable and stable ventricular tachyarrhythmias (VT), as well as differentiate ventricular from supraventricular tachycardias. Right ventricular (RV) pulse pressure has been shown to possess acceptable characteristics as a sensor for incorporation in ICDs. We sought to determine the short-term reproducibility of RV pulse pressure measurements by comparing RV pulse pressure measured during two separate episodes of VT in each of ten study patients. The mean VT cycle length for VT episode 1 was 293 +/- 15 msec, and was 298 +/- 15 msec for VT episode 2 (P = NS). The decrease in mean arterial pressure was 40 +/- 7 mmHg in episode 1 and 37 +/- 7 mmHg in episode 2 (P = NS). The decrease in RV pulse pressure during episode 1 was -13 +/- 2 mmHg, and -12 +/- 2 during episode 2 (P = NS). The decrease in RV pulse pressure during episodes of VT at two different times during a single electrophysiology study is highly reproducible, suggesting that RV pulse pressure may be a reliable sensor over time.

Implantable cardioverter defibrillators: current status and future directions

Sudden cardiac death remains the most common mode of mortality in the United States, accounting for up to 450,000 deaths per year. Survivors of cardiac arrest and patients who have recurrent ventricular tachycardia have a high mortality rate with or without antiarrhythmic therapy. The implantable cardioverter defibrillator (ICD) was introduced in 1980 by Mirowski as a potential treatment for these patients. There are presently over 24,000 implants worldwide and the device has proved to be an effective means of preventing sudden death. The components of an ICD include a generator, defibrillation patches or leads, and pacing/sensing leads. The devices can be implanted with acceptable mortality and morbidity either by median sternotomy, left anterior thoracotomy, subxiphoid, or left subcostal approaches. The long-term results have been excellent with an actuarial incidence of sudden cardiac death of 3% at 5 years. Improvements in battery and capacitor technology, lead design, and tachycardia recognition, combined with the addition of hemodynamic sensors and a better understanding of the science of defibrillation, should lead to further improvements over the next several years in the ICD.

A prospective study of changes in right ventricular dP/dt during ventricular tachycardia

The automatic implantable cardioverter defibrillator (AICD) has significantly decreased mortality in high risk ventricular tachycardia (VT) patients. The AICD provides treatment based on ventricular rate, sometimes leading to high energy shocks in conscious patients with stable VT, or patients with sinus or supraventricular tachycardia. Other physiological parameters, such as maximal positive and negative systolic right ventricular (RV) dP/dt (RV + dP/dtmax, RV - dP/dtmax, respectively), may be included in detection algorithms for future implantable defibrillators. We studied frequency band limited positive and negative RV dP/dtmax before, during, and after 13 episodes of VT lasting at least 40 beats in duration in nine male patients. The mean (+/- SEM) RV + dP/dtmax, dropped by 120 +/- 28 mmHg/sec (P less than 0.001) during the first five beats of VT. RV + dP/dtmax then slowly rose toward baseline levels until a significant overshoot occurred during the first ten beats following VT termination (delta = 234 +/- 58 mmHg/second, P less than 0.002). RV + dP/dtmax correlated poorly with mean arterial pressure (r = 0.32, P greater than 0.1), systolic blood pressure (r = 0.19, P greater than 0.1), and VT cycle length (r = 0.34, P greater than 0.1). Conversely, RV - dP/dtmax rose during the first ten beats of VT (74 +/- 27 mmHg/sec, P greater than 0.05) and then slowly drifted back toward baseline levels. Like RV + dP/dtmax, RV - dP/dtmax overshot baseline levels during the recovery phase (-108 +/- 48 mmHg/sec, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Biosensor applications to antitachycardia devices

Current arrhythmia detection algorithms are unable to adequately distinguish stable from unstable tachycardias; therefore application of a biosensor to antitachycardia devices has been proposed to improve their performance. Right heart pressures and impedance have been investigated for incorporation into these systems. Integration of other parameters (oxygen saturation, preejection period, pH, cardiac output, flow, and temperature) into these devices might also prove useful. The status of these biosensor arrhythmia detection algorithms and their application to antitachycardia devices are described below.