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loss of cardiac resynchronization therapy ( crt ) is a frequent problem that limits the potential benefits associated with this form of non - pharmacological treatment for patients with heart failure.1 it usually occurs in consequence of loss of left ventricular ( lv ) and right ventricle ( rv ) capture , loss of atrial sensing , or loss of atrial tracking due to atrial rates greater than the maximum tracking rate ; however , its presentation at rates lower than the programmed maximum tracking rate is also possible . in this case report , we present a 67-year - old woman with hyperglycemia - induced t - wave oversensing as a cause of crt failure .
a 67-year - old female with a history of diabetes mellitus and renal failure as well as a diagnosis of dilated cardiomyopathy and new york heart association functional classification iii , referred for cardiac resynchronization defibrillator therapy .
a crt - d device is an implantable cardioverter - defibrillator ( icd ) enabled with crt implantation .
echocardiography showed a left ventricular ejection fraction ( lvef ) of 20% and left venricular end - diastolic dimension ( lvedd ) of 60 mm .
basal electrocardiogram ( ecg ) showed a left bundle branch block ( lbbb ) pattern and sinus rhythm . additionally , the patient had serum creatinine ( cr ) of 1.8 mg / dl , blood urea nitrogen ( bun ) of 55 mg / dl , and serum potassium ( k ) of 5.4 mm / dl .
the patient underwent implantation of a dual - chamber insync sentry dr 7298 icd ( medtronic inc .
the icd was programmed to ddd , 60120 beat / min , with a single shocking zone and a rate cut - off of 188 beat / min .
three months later , she returned to the emergency ward due to frequent icd shocks and deterioration of dyspnea .
the results of the admission blood test were as follows : k = 5.2 mg / dl , blood sugar = 560 mg / dl , serum creatinine = 2.6 mg / dl , and bun = 65 mg / dl .
also , the serial cardiac markers levels were within the normal limits , and arterial blood gas measurement did not show acidosis or alkalosis .
the stored electrograms at supine position revealed a ventricular sensing threshold of 6 mv and t - wave oversensing during sinus rhythm ( ventricular sensitivity = 0.5 mv ) .
moreover , atrial and ventricular pacing , sensing thresholds , and leads impedances were unchanged in comparison with previous measurements .
the patient was admitted to the coronary care unit ( ccu ) and treated with insulin to control her diabetes .
after the patient s blood sugar was reduced to 187 mg / dl , another icd interrogation was carried out , which demonstrated no t - wave oversensing at a maximum sensitivity of 0.18 mv . with the patient s permission
, the serum glucose was allowed to increase through a temporary discontinuation of insulin therapy .
two days later at a capillary glucose of 531 mg / dl , intermittent t - wave oversensing was detected at a sensitivity level of 0.5 mv .
after a two - month follow - up period , the patient s serum glucose was well controlled with insulin therapy and she had no further icd shocks and t - wave oversensing , which conferred good biventricular pacing and good response to crt .
t - wave oversensing is the major cause of inappropriate icd shocks ( figure 1).1 different mechanisms having been implicated in the double counting of r and t waves include drugs , hyperkalemia , hyperglycemia variations in sympathetic tones , and alterations in the shape of the intracardiac electrogram.2 , 3 elimination of t - wave oversensing is possible through the correction of reversible causes and device programming , and the repositioning of the ventricular electrode to find a greater r - wave amplitude makes oversensing less likely.35 t - wave oversensing was avoided by considering the following options in the present study : ( 1 ) reprogramming the icd to lower sensitivity ; ( 2 ) implanting the lv epicardial lead for sensing and pacing ; ( 3 ) changing the detection counts ; ( 4 ) administering heart rate slowing drugs ; ( 5 ) repositioning the right ventricular lead to obtain ventricular electrograms with higher amplitudes ; ( 6 ) implanting another endocardial sense - pace lead ; and ( 7 ) prolonging postsens refractory periods . decreasing the sensitivity or programming longer refractory periods can sometimes treat t - wave oversensing , but these measures may interfere with the ability of the icd to correctly detect tachyarrhythmias .
the best option for the treatment of t - wave oversensing due to a reversible cause is the treatment of the underlying cause .
the sensitivity and refractory periods of the device were , therefore , not changed in the present study . in this type of medtronic icd , postsense refractory periods are not programmable .
another option for the prevention of inappropriate shocks due to t - wave oversensing is changing the detection counts ; i.e. , increasing the number of successive counts before the icd is triggered to call the arrhythmic ventricular fibrillation ( vf ) .
appropriate identification and correction of the underlying cause of t - wave oversensing is an essential management strategy . in the case
presented herein , the elimination of t - wave oversensing through a successful control of the patient s blood sugar led to the tracking of the sensed or paced atrial impulses and biventricular pacing .
crt , a technology that simultaneously paces both the left and right ventricles , has emerged as an important treatment tool for heart failure patients with reduced lv function and ventricular dyssynchrony .
there are several possible reasons why as many as 30% of treated patients remain unresponsive to crt .
when a non - responder is identified , the first thing that should be determined is whether the patient is actually receiving crt .
there are two reasons for this problem : first , possible loss of function of the lead in the coronary sinus ; and second , the rapid or ectopic intrinsic heart rhythm ( e.g. , atrial fibrillation or frequent premature ventricular complexes ) .
one should also take into account inappropriate programming or oversensing as the other possible causes of biventricular pacing failure leading to crt failure .
t - wave oversensing occurs when the counter starts giving dual beeps for every cardiac cycle instead of one . 
 this usually happens when the monitoring lead displays a tall t wave , which is also sharp . 
 r wave sensing algorithms of the devices do not sense t wave because the slow rate of the t wave is much less than that of the r wave . 
 but the slow rate of t waves may change with time and also because of parameters like potassium levels and hyperglycemia . 
 we present a 67-year - old female who underwent the implantation of cardiac resynchronization therapy ( cardiac resynchronization and implantable cardioverter defibrilator [ crt - d ] ) because of severe left ventricular systolic dysfunction and ventricular dyssynchrony experienced recurrent inappropriate implantable cardioverter - defibrillator ( icd ) shocks and crt failure . 
 device analysis showed that the crt failure was in consequence of t - wave oversensing due to hyperglycemia . 
 elimination of the t - wave oversensing after hyperglycemia control conferred good biventricular pacing and good response to crt during a 6-month follow - up period .