Cardiac death and stored electrograms in patients with third-generation implantable cardioverter-defibrillators
Eric M. Grubman, MDa,
Behzad B. Pavri, MDa,
Tamara Shipman, RN*,
Nancy Britton, RNa and
Dusan Z. Kocovic, MDa
a Division of Cardiology, Department of Medicine, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
* Ventritex, Inc., Sunnyvale, California, USA
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Figure 1 Stored EGM from the Cadence ICD in a control subject. The EGM is recorded at 256 Hz from a bipolar sensing lead in the right ventricle. The time, in seconds, is displayed at the bottom of the strip. The sharp signals, lasting  100 ms, represent ventricular depolarization. This EGM initially depicts a rhythm, consistent with atrial fibrillation (A). The rhythm spontaneously converts into a more rapid rhythm (B), which meets detection criteria for VT, and antitachycardia pacing is delivered (C) in an attempt to terminate the rhythm. This intervention causes an acceleration of the arrhythmia (D), and a shock is delivered (E), with the resultant termination of the tachyarrhythmia (F) and resumption of a slower rhythm, consistent with sinus rhythm.
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Figure 2 Clinical causes of mortality. Cardiac deaths are divided into sudden cardiac deaths and nonsudden cardiac deaths based on the modified CAST system. EGM signifies the presence of stored electrograms within 1 h of the clinically determined time of death. Wide denotes wide signals on the terminal EGM, >158 ms. Narrow denotes terminal EGM signals >158 ms.
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Figure 3 Relation between EGM width and time between recording and death. EGM width represents the width of the final EGM signal recorded. >1 Hour denotes those deaths that occurred >1 h after the final EGM was recorded. <1 Hour denotes those deaths that occurred within 1 h of the final EGM recording. PIT denotes the EGM width recorded at postimplantation device testing for each patient that subsequently died. The control group represents the postshock EGM width obtained during device testing in patients who did not die during the trial. Device testing occurred immediately after device implantation in all cases. *p = 0.01; **p = 0.05; ***p = 0.91; ****p = 0.03; *****p = .000007; ******p = 0.000007.
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Figure 4 EGM width and cardiac death. Relation between EGM width and cardiac cause of death. EGM width represents the width of the final EGM signal recorded. *p = 0.08.
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Figure 5 Examples of wide EGMs. Panel 1 depicts a wide rhythm, with EGM signals >158 ms (A). This is interpreted as VT by the device, and antitachycardia pacing is delivered (B), without an appreciable change in the arrhythmia. The wide EGM signals continue and become progressively more disorganized toward the end of the episode (C). The device detects a spontaneous termination of the tachyarrhythmia after delivery of antitachycardia pacing. Panel 2 depicts an extremely wide signal that is interpreted by the ICD as VF (A), and a shock is delivered (B). After the shock, the EGM signal remains extremely wide (C), although somewhat less fractionated. The postshock EGM is interpreted by the device as depicting successful termination of VF. Panel 3 depicts an extremely wide signal (A), as well as noncapturing pacing spikes from a permanent VVI pacemaker that had also been implanted (B). The wide EGM is sensed by the device as VF, and a shock is delivered (C), which terminates all spontaneous electrical activity. After the shock, ineffective bradycardic pacing continues (D).
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