A New Approach for AV Optimization

AV and VV optimization are performed through the use of echocardiography or Doppler echo guidance. The reported paucity of optimization in the clinical area has been blamed on many factors: time, money, and lack of skilled cardiac sonographers. As a result, alternative methods of optimization that do not involve echocardiography are being explored. One such approach comes from Inovise Medical, and uses a device called the Audicor^® TS (Inovise Medical, Portland, Oregon). Acoustic Cardiography Acoustic cardiography combines ECG tracing and heart sound patterns to produce data that is used to help determine pacemaker timing intervals. It has its roots in phonocardiography, which is an analysis of heart sounds. It utilizes an algorithm to interpret simultaneous digital ECG and acoustical data, and thus determine hemodynamic parameters. Figure 1 illustrates the interrelationships of the ECG, hemodynamic, and sound components in the normal heart and then in systolic heart failure, and assists in the understanding of how these parameters are used together. Diastolic time intervals illustrated in Figure 1 are the following: Electromechanical activation time (EMAT) is the period of time from the beginning of the QRS until the closure of the mitral valve or S1. Notice how brief this time is for the normal heart, but how this timing is prolonged with systolic heart failure. When the EMAT is shorter, increased contractility occurs and electromechanical delays are shortened. Left ventricular systolic time (LVST) is defined as the time between the closures of the mitral valve and the aortic valve (S1 to S2). Lengthening of this period causes improved ejection fraction. Compare the normal heart findings to the shortened time interval seen with heart failure. Isovolumic contraction time (IVCT) is measured from the point of maximum intensity of the S1 heart sound (mitral valve closure) to the opening of the aortic valve. This period is prolonged in systolic heart failure. Pre-ejection period (PEP) is the electromechanical activation time plus the isovolumic contraction time (IVCT). This is measured from the beginning of the QRS until the opening of the aortic valve. This is an increased time period with heart failure as compared to the normal heart. Left ventricular ejection time (LVET) is the period from the opening of the aortic valve to the closing of the aortic valve. This is greatly reduced in heart failure. Isovolumic relaxation time (IVRT) is the period of time between the closure of the aortic valve and the point when ventricular pressure drops below atrial pressure (aortic valve closure to mitral valve opening). This is lessened in heart failure. The Audicor^® TS measures three different parameters to generate a report. The first of these is the S3. The acoustic energy of S3 is measured over a 10-second period. The values obtained by this measure can vary between 0 and 10 units. The S3 heart sound is generally not audible in the normal heart, but is heard with varying degrees of intensity with heart failure. The second parameter measured with the Audicor device is the electromechanical activation time. As discussed previously, the EMAT is the time period from the onset of the QRS until the mitral component of the S1 heart sound. This is measured in milliseconds. EMAT represents the time it takes for the left ventricle to force the mitral valve to close. This period is lengthened in heart failure. Finally, the LV systolic time is measured. This time period represents the S1 to S2 timing in milliseconds. LVST is reduced in LV dysfunction. Published studies have found a correlation between the strength of S3 and EMAT values, and LV function.^5,6 In addition, LV catheter measurements have correlated EMAT with the dP/dt max in patients with a wide QRS, and LV systolic time with EF.⁷ All of this work has led to the acceptance of EMAT as a parameter to use in AV/VV selection in the patient with bi-ventricular pacing. A clinical comparison of echocardiography to acoustic cardiography has also been conducted, in which end programming results only differed by ? 20 milliseconds for 77% of patients.⁸System Components and Testing The components of the Audicor^® TS system include the console, the Tablet PC, the patient cable and sensors, and a printer (Figure 2). Figure 3 shows a system sensor. The sensors are used to transmit the sound and electrical information to the console. The sensors are placed over the V3 and V4 electrodes during the recording of the ECG (Figure 4). The console receives the information and sends it to the PC. Testing is performed through the sensing of sound and ECG information while various pacemaker AV and VV settings are being programmed. The system's sensors record and analyze 10 seconds of data for each AV and VV delay combination, and display the resulting trends. The report generated includes the strength of the S3, the EMAT and the LVST for each setting combination. An example of this report for AV delay is seen in Figure 5. The goal with interpretation is to locate the AV delay setting that produces the lowest S3 value along with the shortest EMAT and longest LVST; in other words, the pattern that most closely simulates normal hemodynamics. In Figure 5, the AV delay value chosen was 180 ms, as this value most closely met the three above-mentioned criteria. There is a suggestion that use of acoustic cardiography leads to longer AV delay settings and shorter VV settings than those seen with echocardiography-guided optimization. However, in anecdotal reports, the patient response has been at least equivalent and often better with the acoustic cardiography-guided settings compared to echo. Multiple studies are currently underway that are examining head-to-head comparisons of echo versus acoustic cardiography. The use of echocardiography for device optimizations has often been limited by availability, cost, time, and the need for a trained cardiac sonographer. Many times a cardiac sonographer who knows how to perform optimization testing is not available when a patient comes for checks at the device clinic. In addition, Medicare will not pay for multiple echos within one year, thus discouraging optimization from being performed when needed by patients. There is also the issue of consistency in results interpretation among cardiac sonographers. The data produced from acoustic cardiography is objective, so there is more consistency in interpretation among clinicians. Use of Acoustic Cardiography at Prairie Heart Institute Dr. Stephen Jennison, Medical Director of the Heart Failure Program and the Center for Living, Prairie Heart Institute, St. John's Hospital, Springfield, Illinois has been caring for patients with cardiac resynchronization devices since the MIRACLE Trial six years ago. Since that time, the Ritter method for AV optimization has been performed, and then tissue Doppler. Dr. Jennison was approached about four years ago by Inovise Medical regarding the use of acoustic cardiography for device optimization. About six months ago, Dr. Jennison's team started looking informally at the Audicor device, comparing results to that achieved with echocardiography. He writes Post bi-ventricular implant remodeling is seen both anatomically and electrically. We see a decrease in MR, as well as a decrease in heart size, necessitating re-optimization. In the original MIRACLE Trial and InSync III study, AV optimization prior to discharge and at specified follow ups was a part of the protocol and major clinical improvements were seen. Routine practice now does not always include these optimizations, due to time, cost, and lack of availability of trained echo staff. As a result, an expensive piece of equipment is implanted and its full potential for impacting heart failure symptoms is not being seen. Poor response to resynchronization may be occurring because devices have not been programmed adequately and often enough. Nicole Horve, BS, RDCS, FASE, Supervisor of Cardiovascular Services at St. John's Hospital, has instituted acoustic cardiography testing in her department. She noted that the ECG technicians have been trained to perform this testing. Pacemaker reps program the various interval changes while the data is acquired. The testing is usually completed within about 30 minutes for both AV and VV data. The average time with echocardiography was 45 - 60 minutes. The charge for using acoustic cardiography is currently equivalent to the cost of an ECG. One must compare this to the cost of echocardiography. The billing is done under category 99, as there is not a designated billing code for acoustic cardiography at this time. The Prairie Heart Institute's heart failure team has been pleased with the results they've seen with acoustic cardiography-guided optimization, and they plan to continue using this as their optimization method. They are especially pleased with the 50% improvement seen in two of their patients after being re-optimized with this method. The routine AV and VV optimization of CRT devices could lead to a further decrease in patient symptoms, improved quality of life, and better utilization of implanted technology. If these goals can be achieved with a test that costs less, takes less time, and provides equivalent findings, this is a technique to be examined. Acoustic cardiography may well be worth a look.