Dusan Z. Kocovic

Effect of Cardiac Resynchronization Therapy on Left Ventricular Size and Function in Chronic Heart Failure

Background—Cardiac resynchronization therapy (CRT) has recently emerged as an effective treatment for patients with moderate to severe systolic heart failure and ventricular dyssynchrony. The purpose of the present study was to determine whether improvements in left ventricular (LV) size and function were associated with CRT. Methods and Results—Doppler echocardiograms were obtained at baseline and at 3 and 6 months after therapy in 323 patients enrolled in the Multicenter InSync Randomized Clinical Evaluation (MIRACLE) trial. Of these, 172 patients were randomized to CRT on and 151 patients to CRT off. Measurements were made of LV end-diastolic and end-systolic volumes, ejection fraction, LV mass, severity of mitral regurgitation (MR), peak transmitral velocities during early (E-wave) and late (A-wave) diastolic filling, and the myocardial performance index. At 6 months, CRT was associated with reduced end-diastolic and end-systolic volumes (both P <0.001), reduced LV mass (P <0.01), increased ejection fraction (P <0.001), reduced MR (P <0.001), and improved myocardial performance index (P <0.001) compared with control. &bgr;-Blocker treatment status did not influence the effect of CRT. Improvements with CRT were greater in patients with a nonischemic versus ischemic cause of heart failure. Conclusions—CRT in patients with moderate-to-severe heart failure who were treated with optimal medical therapy is associated with reverse LV remodeling, improved systolic and diastolic function, and decreased MR. LV remodeling likely contributes to the symptomatic benefits of CRT and may herald improved longer-term survival.

Exploring Postinfarction Reentrant Ventricular Tachycardia With Entrainment Mapping

Ventricular tachycardia late after myocardial infarction is usually due to reentry in the infarct region. These reentry circuits can be large, complex and difficult to define, impeding study in the electrophysiology laboratory and making catheter ablation difficult. Pacing through the electrodes of the mapping catheter provides a new approach to mapping. When pacing stimuli capture the effects on the tachycardia depend on the location of the pacing site relative to the reentry circuit. The effects observed allow identification of various portions of the reentry circuit, without the need for locating the entire circuit. Isthmuses where relatively small lesions produced by radiofrequency catheter ablation can interrupt reentry can often be identified. A classification that divides reentry circuits into one or more functional components helps to conceptualize the reentry circuit and predicts the likelihood that heating with radiofrequency current will terminate tachycardia. These methods are helping to define human reentry circuits.

Cardiac death and stored electrograms in patients with third-generation implantable cardioverter-defibrillators.

OBJECTIVES We sought to utilize terminal stored intracardiac electrograms (EGMs) to study the electrophysiologic events that accompany mortality in patients with third-generation implantable cardioverter-defibrillators (ICDs). BACKGROUND Despite their ability to effectively terminate ventricular tachyarrhythmias, cardiac mortality in patients with ICDs remains high. The mechanisms and modes of death in these patients are not well understood. METHODS We retrospectively analyzed clinical data and stored EGMs from patients enrolled in the clinical trial of the Ventritex Cadence ICD. Of the 1,729 patients 119 died during 6 years of follow-up. The final recorded EGM was reviewed. Postimplant EGMs as well as 50 control EGMs were used to define normal EGM characteristics. RESULTS There were 36 noncardiac deaths (30%) and 83 cardiac deaths (70%). Of the cardiac deaths, 55 (66%) were nonsudden and 28 (34%) were sudden. When cardiac deaths were analyzed, 46 (55%) had no stored EGMs within 1 h of death, implying that the deaths were not directly related to tachyarrhythmias. In 37 cardiac deaths (18 nonsudden, 19 sudden), stored EGMs were present within 1 h of death. In these 37 deaths, the final EGM recorded was wide (>158 ms) in 33 (89%). Wide EGMs were interpreted as ventricular tachycardia in 27 and ventricular fibrillation in 6. In 13 of the 33 patients (39%) with wide EGMs, therapy was not delivered by the ICD, as it incorrectly detected a spontaneous termination of the arrhythmia. EGMs were significantly wider if recorded within 1 h, as compared with those recorded from 1 to 48 h before death (261+/-124 vs. 181+/-93 ms, p=0.04). CONCLUSIONS Only 37 patients (31%) who died after placement of an ICD had a stored EGM within 1 h of the time of death, suggesting that the majority of deaths (69%) were not the immediate result of a tachyarrhythmia. When EGMs were recorded, they were wide in 89% of patients. These wide EGMs most likely represent intracardiac recordings of electromechanical dissociation. Thus, of the 119 deaths, 112 (94%) were not the immediate result of a tachyarrhythmia.

Characteristics of electrograms recorded at reentry circuit sites and bystanders during ventricular tachycardia after myocardial infarction

OBJECTIVES The purpose of this study was to determine the relation of isolated potentials (IPs) recorded during ventricular tachycardia (VT) to reentry circuit sites identified by entrainment. BACKGROUND Reentry circuits causing VT late after myocardial infarction are complex. Both IPs and entrainment have been useful for identifying successful ablation sites, but the relation of IPs to the location in the reentry circuit as determined by entrainment has not been completely defined. METHODS Data from catheter mapping of 70 monomorphic VTs in 36 patients with prior myocardial infarction were retrospectively analyzed. Entrainment followed by radiofrequency current (RF) ablation was performed at 384 sites. On the basis of entrainment, sites were classified as reentry circuit exit, central-proximal, inner or outer loop sites. Sites outside the circuit were divided into remote and adjacent bystanders. RESULTS Isolated potentials were recorded at 50% (51 of 101) of reentry circuit exit, central and proximal sites as compared with only 8% (11 of 146, p < 0.001) of inner loop and outer loop sites and only 1.8% (2 of 106) of remote bystander sites (p < 0.001). Isolated potentials were also present at 45% of adjacent bystander sites. At central and proximal sites the presence of an IP increased the incidence of tachycardia termination by RF to 47.5% from 24% (p = 0.05). At exit sites tachycardia termination occurred frequently regardless of the presence or absence of IPs (45% vs. 48%, p = NS). Isolated potentials at exit, central and proximal sites had a shorter duration at sites where ablation terminated VT than at sites without termination (20.9 +/- 9.6 ms vs. 35.7 +/- 15.3 ms, p < 0.001). CONCLUSIONS Isolated potentials are a useful guide to sites in the central-proximal region of the reentry circuit, but often fail to identify exit sites where ablation is successful. Entrainment and analysis of electrograms provide complementary information during mapping of VT.

The Etiology of Syncope in Pacemaker Patients

A total of 46 patients with syncopal episodes after VVI pacemaker implantation were studied. Of these, 92% had one to three syncopal episodes and 8% more than three. All underwent a thorough clinical examination, which included chest X ray, echocardiogram, neurological exam, and the following protocol: 24‐hour Holler monitoring, EEG, blood pressure (BP) measurement in three positions, Doppler exam of the carotid vessels, fasting blood glucose, and head‐up tilt table test (60 minutes, 60°). Holter monitoring showed exit block in two patients (4.3%) and failed sensing in one (2.1%). In two patients there was unilateral slowing on EEG. Orthostatic hypotension was found in four patients (8.6%), and hypoglycemia in three insulin‐dependent diabetics. An ocdusive atherosclerotic plaque in the carotid artery was found in three patients (6,5%). Syncope was induced in 17 patients (36,9%) by the tilt table test, after a mean standing time of 47 ± 11 minutes. The mean resting systolic BP of these patients was 140 ± 24 mmHg, and fell to a mean level of 56 ± 8 mmHg (mean systolic BP drop was 79 ± 8 mmHg). Sixteen of these 17 patients with positive tilt table were being paced at the time of syncope and one had a spontaneous heart rate of 73 beats/min. In 14 cases (30.4%) the cause of syncopai episodes after this extensive workup remained unexplained. These results indicate that pacemaker dysfunction is a not major cause of syncopal episodes in pacemaker patients and that these are most often due to vasovagal syncope. Long‐term follow‐up is warranted to determine the prognostic significance of various types of syncope in pacemaker patients.

Survival in 1,431 Pacemaker Patients: Prognostic Factors and Comparison With the General Population

A total of 1,431 patients (mean age 63.4 ± 14.1) with pacemakers (96.2% VVI) primoimplanled between 1967 and 1985 were followed for a mean duration of 78.2 ± 40 pacing months, with 0.6% loss to follow‐up. Cumulative survival for 1, 3, and 10 years was 0.9427, 0.9136, and 0.7536, respectively. There was no significant difference in survival between atrioventricular block (AVB) and sick sinus syndrome (SSS) patients. In addition to age and gender, factors existent prior to implantation that independently affected prognosis included manifest coronary heart disease (CHD), congenital/acquired heart lesions, heart failure, noncardiac internal disease, syncope, and generalized fatigue. After implantation, the most important factor was generalized fatigue, [hen age, stroke, myocardial infarct (Ml), gender (male), heart failure, and syncope. Patients with no underlying disease showed an extremely high cumulative survival (0.9173 at 10 years). Compared to the general population of Yugoslavia, the pacemaker patients showed a similar yearly mortality rate until 1981. After that, elderly males (70+) had a significantly lower yearly mortality than the matched population. Thus, in this large series of pacemaker patients followed into (he most recent period with an extremely low loss to follow‐up, short‐and long‐term survival was very high. Pacemaker patients of any age who are otherwise in good health have an excellent prognosis.

Electrical failure of an ICD lead due to a presumed insulation defect only diagnosed by a maximum output shock.

A 55‐year‐old male patient presented after a single shock caused by oversensing of isolated nonphysiologic signals on both the distal HV and pace‐sense channels. No other abnormalities were found. He subsequently returned complaining of device “vibration” and his St. Jude implantable defibrillator (ICD; St. Jude Medical, St. Paul, MN, USA) was found to be in VVI backup mode and could not be interrogated. Direct testing in the electrophysiology lab showed normal lead impedances and thresholds with an inability to reproduce the abnormal signals. Detailed cine fluoroscopy of the leads found no abnormalities. A new ICD was connected and successfully delivered a 20‐joule shock but failed to deliver a maximum output (39‐joule) shock. The new ICD was again found to be in backup mode. A new Endotak Reliance G lead (Boston Scientific, Natick, MA, USA) was implanted and a maximum‐output shock was successful using a new Fortify DR ICD. This case likely represents a Durata lead insulation defect in the form of an inside‐out abrasion under the distal HV coil. Increased awareness of this defect is warranted, particularly since routine interrogation and submaximum‐output shocks may fail to detect the problem.

Circadian Variations of Heart Rate and STIMT Interval: Adaptation for Nighttime Pacing

DJORDJEVIC, M., et al.: Circadian Variations of Heart Rate and STIM‐T Interval: Adaptation for Nighttime Pacing. In order to determine the optimal pacing rate for pacemaker patienfs at night, 150 normal subjects with regular sinus rhythm and free of manifest heart disease, were studied using 24‐hour Rolter monitoring. Minimum and average heart rates were analyzed on an hourly basis. The study group was divided into six age groups, 25 subjects each, ranging from 20–29 years to 60–69 years. The minimum heart rate during the night was found to be lower than 65 ppm for all groups. The youngest subjects showed the largest variation in the minimum heart rate. The results suggest that an automatic lowering of the pacing rate during the night would allow for longer periods of sinus rhythm, thereby improving hemody‐namic performance and reducing pacemaker power consumption. Suitable sensors for automatic lowering of the pacing rate include inbuilt 24‐hour clock systems and the QT interval that lengthens during sleep.

Elevations in ventricular pacing threshold with the use of the Y adaptor: implications for biventricular pacing.

RHO, R.W., et al.: Elevations in Ventricular Pacing Threshold with the Use of the Y Adaptor: Implications for Biventricular Pacing. Cardiac resynchronization therapy (CRT) is a new and promising therapeutic option for patients with severe heart failure and intraventricular conduction delay. Patients who are candidates for CRT and have a previously implanted device may utilize a “Y” IS 1 connector to accommodate the coronary sinus lead. This modification has the potential to alter biventricular pacing thresholds. During an 18 month period, successful biventricular pacemaker implantation was performed in 72 patients (age: 67 ± 11 years, left ventricular ejection fraction: 20.5 ± 5.6% ). All of these patients had severe symptomatic congestive heart failure (NYHA Class III and IV). In 20 patients a special “Y” adaptor that bifurcates the ventricular IS 1 bipolar output to two bipolar outputs or one unipolar and one bipolar output was utilized. During initial implantation, LV thresholds obtained in a unipolar configuration prior to connecting to the “Y” adaptor were significantly lower than thresholds obtained after connecting to the “Y” adaptor ( 1.7 ± 1.11 V at 0.5 ms pulse width versus 2.8 ± 1.5 V at 0.5 ms pulse width [P = 0.01] ). Two patients (10%) required left ventricular lead revisions due to unacceptably high left ventricular thresholds during device follow‐up. The difference in measured left ventricular thresholds between the two configurations is best explained by a resistive element that is added to the circuit when performing threshold measurement of the LV lead through the “Y” adaptor (combined tip to RV ring configuration) versus measurement of the LV lead in a unipolar configuration. This resistive element represents multiple factors including anode surface area, resistive polarization at the tissue‐electrode interface, and transmyocardial resistance. LV thresholds should be measured in an LV tip to RV ring configuration or ideally in a combined tip (LV and RV) to shared ring configuration in order to accurately assess LV thresholds. This observation has significant clinical implications as loss of capture may occur as a result of improper measurement of left ventricular thresholds at the time of implantation. (PACE 2003; 26:747–751)

Should catheter ablation be the preferred therapy for reducing ICD shocks?: Ventricular tachycardia ablation versus drugs for preventing ICD shocks: role of adjuvant antiarrhythmic drug therapy.

In 1980, Mirowski et al1 implanted the first implantable cardioverter-defibrillator (ICD) in a young female with recurrent ventricular fibrillation and provided an innovative approach to aborted sudden cardiac death (SCD). Although the ICD was considered a treatment of last resort during that incipient stage, subsequent years have witnessed prolific expansion of indications for ICD implantation.2 Several large-scale clinical trials have demonstrated its efficacy for both primary and secondary prevention of SCD in patients with ischemic and nonischemic cardiomyopathy.3,4 ICD therapy in such high-risk patients has been shown to improve survival compared with conventional antiarrhythmic drug therapy alone.3,4 The number of ICD implantations has increased significantly in the last decade, with a concurrent decrease in the use of stand-alone antiarrhythmic drugs for ventricular indications.5–7 Current ICDs have sophisticated programming capabilities, atrial and bipolar leads, and are able to deliver antitachycardia pacing algorithms (ATP) in addition to defibrillating shocks. Response by Kuck on p 705 Typically, patients who receive ICDs are at high risk for recurrent arrhythmia; hence, most patients receive 1 or more ICD therapies for spontaneous arrhythmias after implantation.3 Despite the technological evolution of ICD systems, more than 20% of shocks are due to supraventricular arrhythmia and hence are inappropriate.8–10 The ICD uses ATP or defibrillating shocks to terminate episodes of ventricular tachycardia (VT) or ventricular fibrillation (VF). Although the ICD aborts VT/VF, many patients continue to have symptoms such as dizziness, palpitations, nervousness, flushing, or syncope before receiving an ICD shock.11 When the shock is finally delivered, it is physically and emotionally painful and so noxious that 23% of patients dread shocks and 5% of patients prefer to do without an ICD and “take their chances.”12 A significant prevalence of sadness, depression, and even anxiety disorders have been reported after …In 1980, Mirowski et al1 implanted the first implantable cardioverter-defibrillator (ICD) in a young female with recurrent ventricular fibrillation and provided an innovative approach to aborted sudden cardiac death (SCD). Although the ICD was considered a treatment of last resort during that incipient stage, subsequent years have witnessed prolific expansion of indications for ICD implantation.2 Several large-scale clinical trials have demonstrated its efficacy for both primary and secondary prevention of SCD in patients with ischemic and nonischemic cardiomyopathy.3,4 ICD therapy in such high-risk patients has been shown to improve survival compared with conventional antiarrhythmic drug therapy alone.3,4 The number of ICD implantations has increased significantly in the last decade, with a concurrent decrease in the use of stand-alone antiarrhythmic drugs for ventricular indications.5–7 Current ICDs have sophisticated programming capabilities, atrial and bipolar leads, and are able to deliver antitachycardia pacing algorithms (ATP) in addition to defibrillating shocks.