Letter by Cacko, <i>et al</i> Regarding Article, “Improvement of Cardiac Function by Increasing Stimulus Strength During Left Ventricular Pacing in Cardiac Resynchronization Therapy”
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- Cacko Andrzej
- 1st Department of Cardiology, Medical University of Warsaw Department of Medical Informatics and Telemedicine, Medical University of Warsaw
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- Michalak Marcin
- 1st Department of Cardiology, Medical University of Warsaw
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- Główczyńska Renata
- 1st Department of Cardiology, Medical University of Warsaw
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- Kochanowski Janusz
- 1st Department of Cardiology, Medical University of Warsaw
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- Grabowski Marcin
- 1st Department of Cardiology, Medical University of Warsaw
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Dear Editor,<br>We have read with great interest the article discussing an improvement of cardiac function by increasing stimulus strength during left ventricular pacing in cardiac resynchronization therapy (CRT) by Ishibashi, et al.1) The authors investigated whether increasing stimulus strength of left ventricle (LV) pacing improves LV mechanical dyssynchrony and cardiac function in patients treated with CRT. According to their observation higher stimulus strength may result in statistically significant decreases in QRS duration, septal-posterior wall motion delay, and standard deviation of time from QRS, and increases in LV ejection fraction and LV stroke volume. Thus, increasing stimulus strength of LV pacing in patients treated with CRT improves LV mechanical dyssynchrony and cardiac function.<br>One of the limitations of CRT in clinical practice is the high percentage of patients not responding to the therapy. Clinical or echocardiographic improvement is not recorded in 20 to 45% of patients after implantation of CRT.2) Many physicians used to believe optimal selection of patients and LV lead placement were crucial for efficient CRT. Based on current knowledge we predict that optimal device programming influences cardiac function.3)<br>Ishibashi, et al state that LV pacing with higher energy should result in depolarization of the enlarged myocardial area. Assuming this mechanism is true, it is possible to reduce myocardium depolarization time in patients with suboptimal placement of the LV lead, such as near the infarction area. It is a very important observation as LV stimulus strength is often being programmed close to capture the threshold to save battery life and avoid phrenic nerve stimulation. Moreover, for a long time physicians have been striving to avoid high LV pacing energy to reduce the risk of anodal pacing.<br>Influenced by Ishibashi, et al we decided to check if increasing stimulus strength of LV pacing would affect cardiac function in our patients who were not responding to CRT. We chose two men with significant QRS complex narrowing when increasing the energy of LV pacing and carefully assessed LV function with echocardiography. Both of them had ischemic heart failure with significantly reduced ejection fraction (25% and 15%). First, we assessed QRS complex width, rate of LV pressure rise [dP/dt], and LV velocity-time integral [VTI] pacing at LV capture threshold. Then, we assessed those parameters doubling the energy of LV pacing. Our observation was consistent with the results of the trial; LV systolic function was more efficient when conducting LV pacing with increased energy (Table).<br>We must remember that increased stimulus strength results in increased energy consumption and faster battery depletion. Reducing device battery longevity may increase the number of device replacements in a patient’s lifetime. However, CRT is a treatment option for symptomatic patients on top of optimal heart failure therapy. Only responders benefit from CRT. In our opinion if no clinical (or other) symptoms of improvement are observed and the patient is classified as a non-responder, every possible and rational opportunity should be evaluated – even if it results in faster battery depletion.<br>Based on our review of the literature and on our observations, we are strongly convinced that the results of the published trial may have significant influence in clinical practice. We would like to encourage Ishibashi, et al to perform a longterm observation to confirm the possible positive impact of increasing stimulus strength of LV pacing on the response to CRT.
収録刊行物
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- International Heart Journal
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International Heart Journal 56 (5), 578-579, 2015
一般社団法人 インターナショナル・ハート・ジャーナル刊行会